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KW TS-930S PS trouble




 
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KA2PTE
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« on: January 10, 2023, 08:19:25 AM »

Working on one of these with the notorious PS problems. It saw a prior fail that took out the RF driver transistors and someone went with 12V driver transistors (2SC1969's) and a 1A 12V regulator, but the regulator blew out.

I know about the new PS available, but am curious the problem with the original PS design to try and keep it
in there due to costs. Another ham in the UK that retained his old PS said he placed 28v muffin fans on the
28V feed to help supress the notorious spikes on the line, which eventually cause the original driver transistors to blow, and likely caused the 12V regulator I saw fry in there as well.

I wanted to know how large the spike is, so I set my Fluke DMM to min/max and plugged in the AC to the rigg.
(with the KW power sw off) It immediately put out a loud BLEEEP ! and remained bleeping , displaying: OL on the readout. So whatever its seeing, its quite nasty. I placed a 48V MOV on the line, tried again, and no BLEEP...max said 31.5V , which is where it stays till you unplug AC power and after a min or so it gradually falls. If you keep AC plugged in, and hit the power sw you get 28.5V exactly which is on the mark.

Another ham who works on these alot said "The reason you continue to see voltage on the pass transistors is due to the legacy AC wiring.  Japanese manufactured products from the 1970s and 1980s all followed a convention to switch the Neutral AC line across the front panel switch.  This leaves the HOT AC line active on the transformer all the time when the radio is plugged in.  When you measure the pass transistors, you are measuring the output of the high side of the transformer in relation to chassis ground, which is tied to neutral at the source in 3-wires systems that are NEC compliant in the U.S.  This is not only dangerous since the HOT AC is always present and is contrary violation of NEC code and should be corrected.   If you use the radio in a GFCI circuit, it will result in intermittent breaker trips.  "

I have studied the schematic and cant see how the neutral is on the panel switch. Perhaps someone here can explain whats going on? I have a decent scan located here : 
https://www.mediafire.com/file/m4kvelb3w5fwwf8/TS-930_schematic.pdf/file


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ki4nr
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« Reply #1 on: January 10, 2023, 06:40:40 PM »

The 28.5 volt overshoot spikes is caused by the regulator circuit unloading at power down to correct this put a 22k resistor across D-7,  goes from Q-1 collector to ground that will stop the 28.5 volt spike on power down.  
1/8 or 1/4 watt is fine.

Rebuild the power supply with good parts and use 2N5886 for the pass transistor if you can find them. Another good pass transistor are MJ802G  mouser has them. Change the caps too.

I don't know what 930 version you have. There were many changes over the years. On the AC side of the power supply early models had a relay to switch the AC to transformer primary and latest 310 serial number the front panel switch did the switching of AC and 21 volt DC sub supply. Some schematics are not accurate in that regard.

No matter what, when you shut the radio off the transformer AC input turns off like any normal power supply so check the AC relay if you have that version, check the front panel switch if you have the later version. The later version many times has the contact welded in the AC side front panel switch.  Powering off the front panel switch, means no power anywhere !!

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KA2PTE
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« Reply #2 on: January 10, 2023, 11:19:40 PM »

Ok interesting. This is an early SN, it has the relay for the primary of the power xfmr. The AVR board
is the older version so it does not have the 5 pin jack on it (j7) as shown in the PDF.

The power switch has a DC side and an AC which powers the relay for the main xfmr.

I noticed when you hit the power switch the spike happens,  and you get the 28V till you turn the switch
off, then it jumps to 31 and rests there a while. Will try the 22K resistor.

After more study, I thought Q1 was being kept biased by C6 still loaded up with 28V
and C4 will still be charged as will the bridge caps, so that resistor on D7 may be able to help.
D7 is a RD33FBD-B1, and with a search found this doc explaining the entire PS circuit, says its a 33V zener.

https://docplayer.net/7037156-Circuit-analysis-and-improvements-of-the-ts930s-power-supply-unit-switching-off-your-rig-can-kill-the-driver-transistors.html

Looks like its also talking about the 22k resistor you mentioned.


 

The 28.5 volt overshoot spikes is caused by the regulator circuit unloading at power down to correct this put a 22k resistor across D-7,  goes from Q-1 collector to ground that will stop the 28.5 volt spike on power down.  
1/8 or 1/4 watt is fine.

Rebuild the power supply with good parts and use 2N5886 for the pass transistor if you can find them. Another good pass transistor are MJ802G  mouser has them. Change the caps too.

I don't know what 930 version you have. There were many changes over the years. On the AC side of the power supply early models had a relay to switch the AC to transformer primary and latest 310 serial number the front panel switch did the switching of AC and 21 volt DC sub supply. Some schematics are not accurate in that regard.

No matter what, when you shut the radio off the transformer AC input turns off like any normal power supply so check the AC relay if you have that version, check the front panel switch if you have the later version. The later version many times has the contact welded in the AC side front panel switch.  Powering off the front panel switch, means no power anywhere !!


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« Reply #3 on: January 11, 2023, 12:49:18 AM »

Ok ... You got the old model with the super simple power supply. It has no 21 volt sub supply and should have a bank of power resistors behind the Antenna tuner in an aluminum enclosure. The DC side of the power switch send 28.5 volts to the bank of resistors that powers the whole radio.

The 22k resistor mod still applies to that old AVR board and will correct the spike issue.  D-7 is a 33 volt one watt zener.

Be sure to replace Q-1 with the better part like whats in the newer 930's  I believe it was a 2SB861 or its equivalent

The pass transistors are very important to replace too with better parts like 2N5886, MJ802G, MJ15003G

Also change the three caps with 2200uf 50 volt snap in types. That power supply is very reliable when upgraded with newer better modern parts

Also when you buy parts do NOT buy from Ebay !!  Most all parts are counterfeit, buy only from Mouser or Digikey or known reputable vendors
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Tom W2ILA
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« Reply #4 on: January 11, 2023, 08:02:44 AM »

If you ever are inclined to change out the entire power supply, take some time to go through this site: https://www.w3afc.com/

My early 930 had multiple  common pass/final transistor failures.  Scorches on the AVR pcb made repairs more difficult.  I was an early adopter of the Compudigital supply for my early 930 and it has been running beautifully.  The hardest part was commiting to the swap. This is a major architecture change and not for everyone.  My supply was a smaller version rather than the 20/26 that people use today in the kits. 

W3AFC has also done nice work testing alternative final transistors should you ever need to replace them.
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KA2PTE
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« Reply #5 on: January 11, 2023, 01:44:22 PM »

Yes, have heard about the power resistor bank, they say its very inefficient,
and I think the newer 930's dont have it, and the 21V from the AVR replaces it?

For sure lots of counterfeit semi's on ebay, I try to avoid unless its an American
seller and something simple like a resistor or something.

The pass transistors are Onsemi 2N5886G's, they look new, checked on on the teter.
They were feeding a mere 7812/1A regulator on the PA, which probably eventually shorted
with those spikes. The AVR fuse didnt blow as it was drawing less than an amp with the short
so the pass transistors held up ok.



Ok ... You got the old model with the super simple power supply. It has no 21 volt sub supply and should have a bank of power resistors behind the Antenna tuner in an aluminum enclosure. The DC side of the power switch send 28.5 volts to the bank of resistors that powers the whole radio.

The 22k resistor mod still applies to that old AVR board and will correct the spike issue.  D-7 is a 33 volt one watt zener.

Be sure to replace Q-1 with the better part like whats in the newer 930's  I believe it was a 2SB861 or its equivalent

The pass transistors are very important to replace too with better parts like 2N5886, MJ802G, MJ15003G

Also change the three caps with 2200uf 50 volt snap in types. That power supply is very reliable when upgraded with newer better modern parts

Also when you buy parts do NOT buy from Ebay !!  Most all parts are counterfeit, buy only from Mouser or Digikey or known reputable vendors

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« Reply #6 on: January 11, 2023, 01:48:02 PM »

Roger that, I know of that new PS and many hams said to give it a try,
but I am the type who tries to not throw out useful parts like the transformer
if it can be helped. Apparently its a torroidal design, according to KW's tech
reports so it will be low noise / RFI compliant.

I sent W3AFC an email, never got an answer, but yea lots of good stuff on that site.


If you ever are inclined to change out the entire power supply, take some time to go through this site: https://www.w3afc.com/

My early 930 had multiple  common pass/final transistor failures.  Scorches on the AVR pcb made repairs more difficult.  I was an early adopter of the Compudigital supply for my early 930 and it has been running beautifully.  The hardest part was commiting to the swap. This is a major architecture change and not for everyone.  My supply was a smaller version rather than the 20/26 that people use today in the kits. 

W3AFC has also done nice work testing alternative final transistors should you ever need to replace them.
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« Reply #7 on: January 11, 2023, 06:24:51 PM »

You can change over to the newer switching supply if you want but it's not necessary. The old power supply is super simple and reliable when parts are replaced with newer robust typed. I have restored about (35) 930's and about (50) 940's over the years and have never had a power supply fail after rebuilding them with better parts.

Good you have the 2N5886 pass transistors those are the best type for the job and what I used on all my rebuilds. They can handle anything. Unfortunately they are no longer available and obsolete. Use the MJ802G or MJ15003G. The main reason for the power supply blowing up is Kenwood use the 2N5885 as the pass transistor. That part is only rated at 60 volts and the input to it is around 43 volts depending on your AC line. Way to close and a few AC s spikes and it fails and takes out other parts on the AVR board. Also if your radio still is using the thermo pads on the pass transistor change over to mica and thermal compound, much better.

For cooling, you can use the stock fan setup and it's fine. But to improve, use a 24 volts computer fan and put a dropping resistor inline to slow it down. Power the fan from the 28V line. Also I find blowing air into the heatsink fins cools better then drawing it out like Kenwood did.

On the driver replacement I use Mitsubishi 2SC1969 and ran them on 18 volts with 1.5 amp regulator. Trying to find original 2SC1969 is about impossible now all are counterfeits. The transistors are good for 25 volts collector to emitter. The IMD distortion is lower and the regulator has to dissipate less wattage. Set the idling current at 125 milliamps. Never had a failure with that setup and radio has full output and low distortion , actually better that the original Motorola MRF485

Be sure to run a wire in the mechanical feed thru's on the Final board, the have a habit of going intermittent. Plenty of info on net for that. Plus it would be a good idea to replace all the carbon resistors in the final unit amp circuits.

Use this regulator for the drivers  L7818CV-DG

https://www.mouser.com/ProductDetail/STMicroelectronics/L7818CV-DG?qs=WHlX%252B%252B9%2FRwDN5eTUn%252BQLtg%3D%3D
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« Reply #8 on: January 11, 2023, 07:04:32 PM »

Wow, great stuff.

Yes, I put in a pair of 2SC1969's but there are reports lots of chinese fakes out there
that will go into self oscillation, so I am wary.

Also put in Mica insulators and compound, not a big fan od the pads....tho seems KW used them in
alot of stuff.

I used an SI-3122V 12V/2A (TO-3PL) regulator with 0.01uF decoupling caps on the in
and out leeds. The spike killed it though before I had a chance to test the PA properly
and yes I heard 120mA is a good idle for them. Didnt know you can go up to 18V, will
keep that in mind.

Not sure what the "mechanical" feed thru's are. I did see they placed the round lug
under the original driver transistors, so there was kinda a gap when thats done
and I put the lug on top of the tabs and used compound on all the surfaces.

The SI-3122V has the metal tab as the positive input so I had to use an insulator so it didnt ground.
I have a couple of original SANKEN brand spares , so I am glad I thought of keeping some in stock.
Was told the drivers could see up to 2A on voice peaks, so the regulator with the good heat sinking ought to
be ample. Only trouble is that spike, which killed it, and the resting 31.5V after u kill power probably helped
blow it as its only rated for 30V max on the input side. I have some resistors coming in to drop it 10V for 2A,
but at Idle with 120mA, the resistor is only gonna drop about 2v, so am concerned about that a little.....


Oh and did u also reduce the values of the 220 ohm and 33 ohm resistors when you put the new drivers in?



You can change over to the newer switching supply if you want but it's not necessary. The old power supply is super simple and reliable when parts are replaced with newer robust typed. I have restored about (35) 930's and about (50) 940's over the years and have never had a power supply fail after rebuilding them with better parts.

Good you have the 2N5886 pass transistors those are the best type for the job and what I used on all my rebuilds. They can handle anything. Unfortunately they are no longer available and obsolete. Use the MJ802G or MJ15003G. The main reason for the power supply blowing up is Kenwood use the 2N5885 as the pass transistor. That part is only rated at 60 volts and the input to it is around 43 volts depending on your AC line. Way to close and a few AC s spikes and it fails and takes out other parts on the AVR board. Also if your radio still is using the thermo pads on the pass transistor change over to mica and thermal compound, much better.

For cooling, you can use the stock fan setup and it's fine. But to improve, use a 24 volts computer fan and put a dropping resistor inline to slow it down. Power the fan from the 28V line. Also I find blowing air into the heatsink fins cools better then drawing it out like Kenwood did.

On the driver replacement I use Mitsubishi 2SC1969 and ran them on 18 volts with 1.5 amp regulator. Trying to find original 2SC1969 is about impossible now with many counterfeits. The transistors are good for 25 volts collector to emitter. The IMD distortion is lower and the regulator has to dissipate less wattage. Set the idling current at 125 milliamps.  Never had a failure with that setup and radio has full output and low distortion , actually better that the original Motorola MRF485

Be sure to run a wire in the mechanical feed thru's on the Final board, the have a habit of going intermittent. Plenty of info on net for that. Plus it would be a good idea to replace all the carbon resistors in the final unit amp circuits.

Use this regulator for the drivers  L7818CV-DG

https://www.mouser.com/ProductDetail/STMicroelectronics/L7818CV-DG?qs=WHlX%252B%252B9%2FRwDN5eTUn%252BQLtg%3D%3D

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« Reply #9 on: January 11, 2023, 09:23:06 PM »

That SI-3122V regulator you used has way to low input specs. 30 volt is disaster that has happened. The L7818CV-DG input spec is 35 volts so it's fine and there's really is no other ones that are higher.

The 220 ohm feedback resistors and 33 across the input transformer I left at stock values. But I did change them because of the values being off from age and heat. Also change the R-10 and R-9 to new ones. Same 22 ohm value.

The feed thru's on the final board are those rivets that connect one side of the board to other side. If those go open or intermittent the drivers are not connected and blow up. So put Z bend wire thru them and all the others on the board.

The one thing I did do is modify the bias circuit per kenwood TS-940 service bulletin SB-988 it amounts to changing R-16 from 1.2k to 2.2k  which lets the tracking diode's have better control on the bias's.


* TS-940S MFR-485 Driver Transistor Changes (Blue Dot) A.jpg (81.13 KB, 640x803 - viewed 88 times.)

* TS-940S MFR-485 Driver Transistor Changes (Blue Dot) B.jpg (29.03 KB, 803x640 - viewed 92 times.)
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KA2PTE
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« Reply #10 on: January 12, 2023, 08:50:07 AM »

Ok very good.

2SB861 is the original Q1 in there.

Yes, I will reverse the connections on the PS fan, I guess the PA
fan would benefit from that as well?

I read if you lower those feedback resistors, its an improvement
of sorts so I lowered them.

I am gonna try and pull the board out to put the 22k resistor in.
There was what I think is a redundant gnd wire, I left hanging.
I suspect it went to the bridge or the large caps, but I read chassis ground
to the AVR board, the bridge and the caps, so I guess I can remove it?

Update:

I got the 22K in there but left Q1 alone. The big lug with the thick wires
to the 28B side of the fuse cold worked loose as I finagled the board.
After fixing that, inspected the pass transistor connections and one wire
I didnt solder good enough broke off the pin, so had to redo that.

When I powered up, PS was dead, then I thought what did I do with that
extra ground wire...I left it in and it was shorting something out down there.
I removed it and luckily, there was no damage and I now have a nice 28V
with no jump to 31V on power off like I did before.

My Fluke is still freaking out tho, when checking min/max like it did before.
So I guess the spike is still there.





* HPIM1141.JPG (602.43 KB, 1200x944 - viewed 93 times.)
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« Reply #11 on: January 12, 2023, 04:24:27 PM »

You can lower the feedback resistors if you have 2SC1969 drivers that have a high Hfe. All my 1969 were of low Hfe so I did not have to do any of that and were completely stable. That thin black wire is a dedicated AVR ground that goes to chassis.

The AVR board gets ground multi ways, from the two top screws on the board to the mounting bracket, to the heavy black negative wire to the final unit. But for some reason kenwood felt it needed that thin wire to ground too.

The only reason I can think of why they did it is, if you were troubleshooting the AVR board and had the final unit power leads (the negative specifically) disconnected and had the board physically out of the chassis floating while testing it would then have no ground in that scenario.

If I remember right ( I have not worked on a 930 or 940 in many years ) there is a lug the down low on the chassis next to the AVR board, I think a heavy black negative wire goes there too. That's were the thin black wire goes.

Leave the final unit fan alone, as it came from the factory. It works best as kenwood has it blowing air into the fins.

What spike are you talking about measured with your fluke meter ??
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« Reply #12 on: January 12, 2023, 05:22:27 PM »

The old 930 brought back memory's so I found my old picture files of when used to work/restore on them. I use to redress all the sloppy ass wiring that kenwood did and detail all that to perfection along with the proper size cable ties.   I even found a picture of a AVR board and setup that I rebuilt for a guy in Australia too.


* TS930 AVR.JPG (73.54 KB, 640x480 - viewed 99 times.)

* TS930 Power Supply 1.JPG (75.87 KB, 640x480 - viewed 99 times.)
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« Reply #13 on: January 12, 2023, 05:24:44 PM »

More pic's. If you notice the last picture is the power supply that's in your old serial number radio


* TS930 Rewire1.JPG (97.07 KB, 640x480 - viewed 95 times.)

* TS930 Power Supply to Australia.JPG (24.34 KB, 640x480 - viewed 103 times.)
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« Reply #14 on: January 12, 2023, 10:53:11 PM »

Its on the 28V line, I set the Fluke DDM to DC min-max record
and upon power up, the display reads: OL and it beeps constantly.

I have a big 40KV DC probe that goes into any DMM for reading really high
volts, and the DMM does not go beserk with that, it says the max is 32VDC.

I remember jiggling the Fluke leeds with one hand on the pos, and it seemed to freak out,
so maybe its a false positive.

I dare not use the SI-3122V with that overshoot, and it seems the datasheet on the 3122V is wrong.
They claim input is center pin but when I tested on a bench supply the input is pin1, output is 2 and gnd is 3.
With no load it puts out 13V with about 16V on the input. However, when I placed a 330 ohm resistor as the
test load, which is only about 60mA current, the output went from 13 to 5. So this is a terrible regulator
and surprising to see Sanken create a dud like this.

I will go with the L7818CV-DG you mentioned.

Roger on the photos and the ground wire, I think you are right on the chassis ground post, I saw it
near the screw to the AVR frame down there.

Certainly one heck of a project, but very interesting. Thanks for your expertise. I will post the
next point of progress here once the regulator arrives.

 Smiley



What spike are you talking about measured with your fluke meter ??
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« Reply #15 on: January 13, 2023, 06:07:05 AM »

On the regulator you may want to be on the safe side to use the 15 volt L7815CV-DG version. I don't know if you have original Mitsubishi 2SC1969 and what Hfe they have. I did not have any problems running mine at 18 volts but they were very low hfe. So 15 volts would be safer. Same idling current at 125 millamps.

Not sure on the spike the fluke is reading. I did all my testing with an older fluke 77 before all that min/max stuff came out. Like everyone noted, the only issue with the circuit was the power down 28 voltage rising.

Buy the way, kenwood on very late 930's and new 940's added that 22k resistor update. But they never had a service bulletin on it and or updated the schematic. The AVR board was never update on the 940 and they just soldered that resistor on the foil side thru out the whole production run of the 940.

Then the excellent TS-950S came out which had ZERO power supply problems. Interesting, in all my years of servicing radios I never had to repair a TS-950 power supply and the circuitry was very similar to the 930 & 940's

I would say the bad reputation the power supply got was for two reasons, Not having that 22k resistor & voltage rising on power down blowing voltage fragile MRF485 and using way to low voltage 2N5885 pass transistors and those shorting collector to emitter putting 43 volts on everything destroying parts on the AVR board and blowing the drivers. Also I'll never understand why kenwood stayed with the 2N5885 which were not right for the voltage involved when Motorola had much higher voltage better parts available in their TO-3 case transistor line.

Just replace all parts as we talked about and that's really it. It's super simple primitive power supply and very reliable with newer better parts. My 930 and 940 have been going strong for over 20 plus years since I restored them in 1998



https://www.mouser.com/ProductDetail/STMicroelectronics/L7815CV-DG?qs=T%2FOtf55vL7fQ8ZCL4uIjcA%3D%3D
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« Reply #16 on: January 13, 2023, 07:17:22 AM »

You got me thinking on voltage regulators and I found a higher current models from ST Micro. Both from mouser and rated at 2 amps in both the 15 & 18 volt versions. They are the thinner single gauge models meaning the mounting tab is thinner metal but from what I read the dissipation is the same. The DG version ( Dual Gauge ) is the thicker tab which seems not to be available.


https://www.mouser.com/ProductDetail/STMicroelectronics/L78S15CV?qs=v7fRTcZn1IeUYNcrkUDSWg%3D%3D


https://www.mouser.com/ProductDetail/STMicroelectronics/L78S18CV?qs=GGwmtXQPF%2FnQmfjz7QpSVQ%3D%3D
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« Reply #17 on: January 13, 2023, 10:52:26 AM »

I ordered some of the L7818CV-DG, 35Vmax/(1.5A), and some L78S12CV
35V max/(2A). Also discovered Rohm makes a 12V/2A with a plastic tab
BAJ2DD0T so ordered some of those too.

Datasheet says typical input is 4-25V but absolute max is 35v...
and the peak is 50V so I may try the Rohm one first. I have some 6A
silicon diodes from another project that I suppose I could place in series
to drop it a little if its a problem, or with the 18V regulator, do the same to
tweak the output dwn to 15 as you said. 6A a little overkill, probably ought to have
researched some 2A ones before I completed the order.
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« Reply #18 on: January 13, 2023, 06:11:04 PM »

I think the Rohm BAJ2DD0T is not going to handle the voltage. The L7818CV-DG is a safe deal with it's 35 volt rating. Anyways try them out and let me know on the results.
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« Reply #19 on: January 18, 2023, 05:19:51 PM »

Got the regulators, and I put the ROHM one in first for a
try. I also got a bunch of SMT 600V/2A diodes, and I have (6)
in series to get about a 3V drop to the regulator as a buffer.

Powered up, have a good 28V to the PA, the diodes bring
the volts to the reg to about 24.7v, the regulator puts out 12v
exactly.

Tried to key tx in tune on CW, dont see any power out,
then I realized I left the Tx-on connector off the PA.


I let her sit there in Rx a while, the PS heat sink gor kind of hot
after maybe 7 mins, waited for the fan to come on, it eventually did,
and cooled the sink blowing air into it, then turned ott after a couple mins....
and the sink was much cooler, so I guess thats normal? I do have the resistor changes in
there for the fan to come on sooner, and run a little faster. The 12K thermistor had broke on me,
and I found one on Digi Key, a 12K enclosed in a ring terminal, so I guess its working.

Also I saw the schematic took the Vcc for the drivers from the main 28V line, but the
stuff out there had you lifting the L17 connection....which I thought went to Q7. I have my feed
on the cathode of D1 which is how the drawing is.

With the Tx-on connector hooked up, I do see idle current on the feed to the drivers,
and was able to adjust the pot for 120mA and the final current for 1.3A on USB.

Went to Tune, and CW into the dummy load, and there is a brief level of good power, then
it falls immediately to about 6w. I tested modulation on SSB, seemed to sound ok, then I hit the proc
switch, now it wont modulate at all.

ALC meter setting is pegged all the time. Seems if I put the meter switch to compression setting,
the power level returns up to 100W or so.

I set it down to TUNE, and let it run there a long time into the DL. PA gradually got pretty hot,
as soon as I thought there was gonna be an issue, the fan finally did come on, so that looks like
its working properly.







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ki4nr
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« Reply #20 on: January 18, 2023, 08:32:11 PM »

First thing is to check the negative voltage on the bottom main board. R-400 runs hot & deteriorates from heat and soldering on board too. One side of R-400 should be around -40 volts the other side will be -12 volts  D-210
is a 12 volt zener that sets the voltage.

If all that is fine, then make sure of all the pots in the ALC circuit,  VR-13 set the base ALC voltage at 3.2V,  VR-9 set SWR protection and VR-10 sets current limiting

VR-11 and VR-12 set the ALC meter. Both ALC meter zeroing and ALC meter scale. Maybe those were screwdrivered

All this is in the service manual  Let me say also Soldering issues and intermittent plugs / switches by oxidation is major problem in fixing those radios. Actually in any old radio regardless of make.

Sound like you got one of those project 930's that has been hacked & butchered by hams over the years. I have worked on those before and have spent countless hours bringing them back to life.

90 percent of hams should not own a soldering iron and should never even look inside of a radio. Don't get me started on newer SMD component radio. The butchery I have seen on those over the years is unreal.
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« Reply #21 on: January 18, 2023, 10:00:30 PM »

Ok will check that stuff you mentioned.

I work the KW Hybrids alot (TS530/830) and they have a mod where you place
negative feedback on the ALC pin to reduce power out to go down to QRP,
or use a linear easier. I wonder if there is something with the ALC circuit
doing that, or could it be the 2SC1969's I used are not ok with those decreased
resistor changes I did?

I dont get why selecting compression with the meter switch gives you full power.
I did notice the mike jack is a bit loose, like someone was working on it.
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« Reply #22 on: January 18, 2023, 11:11:32 PM »

I looked at the schematic and see no reason why just putting the meter switch in comp position would affect the power output.

Normally when the proc switch is Off & you put the meter switch in comp position it will read nothing until you turn the proc switch on, then you set the compression level from the processor " In " front panel pot and the meter will respond as you talk.

Can you see if anyone did any modification to the radio ??

It's possible the 1969 are oscillating, but that normally would make the ALC go nuts. The comp switch affecting power is a new one on me.
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« Reply #23 on: January 19, 2023, 12:44:19 AM »

Nothing immediately obvious like mod work at a casual inspection. All the connectors seem seated ok
on the main board.

I know with that ALC mod on the KW Hybrids I mentioned, if you have it applied,
and you set the meter sw to ALC, its usually pegged. Because I guess of the negative feedback
from the 9v battery in reverse on the ALC line. So perhaps thats applicable to these radios as well.

Does the driver section connect to the ALC circuit somehow in the schematic? ALC
meter is pegged whenever I am in tx, so its def goin nuts.

I was told there are cheap chinese 1969's out there, prone to self oscillation
if used in this kind of config. The ones in there now were given to me by another ham,
not sure where he got them. They were not perfectly matched beta, but close. The ones
that were in there were perfectly matched, cant remember what they measured for gain on
my tester tho. I remember reading that lowering those "feedback" resistors helps stability
but you said only if the gain is low. Perhaps if its high, it de-stabilizes?

Months ago I was gonna bench test the PA, someone said put 50 ohm load resistors on the
output RF and the input for "balance" to do an idle current test. When I applied 28V, the
resistor on the output jack fried - it was only 0.5W and with the input jack basicly tied thru
gnd, in / out were connected, so I figured it was natural self osc of some sorts. But now I think
it could be these 1969's. Since I have the tabs above the pcb now, they will be simpler to swap out,
maybe I will try the originals which are a perfect matched pair.

Also this site says there are subs for the 1969 (2SC1969 > 2SC1944 2SC2050 2SC2098)
https://masterelectronicsrepair.blogspot.com/2020/08/table-of-2sc-series-transistor.html
Dunno how accurate it is.







I looked at the schematic and see no reason why just putting the meter switch in comp position would affect the power output.

Normally when the proc switch is Off & you put the meter switch in comp position it will read nothing until you turn the proc switch on, then you set the compression level from the processor " In " front panel pot and the meter will respond as you talk.

Can you see if anyone did any modification to the radio ??

It's possible the 1969 are oscillating, but that normally would make the ALC go nuts. The comp switch affecting power is a new one on me.

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ki4nr
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« Reply #24 on: January 19, 2023, 01:17:29 AM »

What the radios current ( IC ) meter reading when the ALC is pegged ??

If it's oscillating it will be pulling current above idling as a sign.

Simple test, Disconnect the 28 volt power from the final unit to disable it. If the ALC meter goes back to Zero in transmit then the final unit is oscillating.

If it stays peg out in TX with the final unit disabled, then the problem in the bottom main board.

All this is providing that the ALC zero pot on bottom main board is adjusted correctly to zero out the meter

The ALC signal is from the directional coupler circuit in the low pass board. The forward ( D-15) diode provide rectification (VSF) to ALC circuit and ( D-16) reverse diode (VSR) for SWR protection.

Same basic circuit setup used even today on the newest radios.
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