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32V-2 no grid current - how to troubleshoot




 
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Author Topic: 32V-2 no grid current - how to troubleshoot  (Read 552 times)
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KJ4OLL
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« on: September 25, 2017, 06:40:42 PM »

My 32V-2 has worked for years on 75M.
Now there is no grid current.
Plate current 40 mills
Grid current zero
HV = 600 (I have the switch set to the lower value)
LV= 300
RF output = 0

I am not confident that I could troubleshoot/repair this myself, as I can find very little information about this unit other than what is in the manual.

A couple of guys told me that when their 32V-2 did this, a shorted screen bypass cap. on the 4D32 socket was the problem.

I looked in there, it appears to have been “designed” so as to make repair impossible. What a mess.

Anyway, it has been suggested that I start by measuring  the DC voltages around the final and driver.
Not sure of how to configure the test equipment.
I have a signal generator, and can inject a signal into the mic jack.
With the HV off and the LV on, should I be able to find a signal in these circuits?

Also, I found these test points next to the socket, but because of the way everything is jammed in there, can't tell what they connect to.


Plan "B" is to sell it to someone else that can fix it, or "C" scavenge the parts out of the chassis and sell them?

73
Frank
KJ4OLL


* 32v2testpoints.jpg (801.84 KB, 1200x1600 - viewed 54 times.)

* 32v2_4D32socket.jpg (841.78 KB, 1200x1600 - viewed 65 times.)
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KA2DZT
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« Reply #1 on: September 25, 2017, 07:11:12 PM »

Most likely a failure of a component.  Put away your signal generator that's not going to help you.  Hopefully you have a VOM or some type of DVM.  There are plenty of folks on this forum that know that xmtr forwards and backwards.  I'm not one of them since I only have my own HB xmtrs. 

You should get some help soon.

If your set worked well for years it shouldn't be a big deal to get it working again.  May just be a tube that went south.

Fred
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KJ4OLL
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« Reply #2 on: September 25, 2017, 09:04:54 PM »

I wish it was a tube, but I tested them all, except for the 4D32.
I don't have the socket adapter for this tube for the TV-10.
But I had spare 4D32's to swap in, no change in symptoms, so I do not suspect the 4D32.

So one or more components in these is the culprit:
 PTO not working
 Buffer not working
 Freq doubler not working
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KA2DZT
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« Reply #3 on: September 25, 2017, 09:38:38 PM »

With all those circuits not working I would begin checking the low voltage B+ circuit.  Could be no B+ is reaching those circuits.  Not sure if that xmtr uses a clamp tube circuit on the final.  With no grid drive the clamp tube will drag down the final screen voltage limiting the final plate current to a safe level, something like you have, about 40 ma.

Fred
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KC4VWU
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« Reply #4 on: September 26, 2017, 02:17:22 AM »

First thing to do is don't flip out. I'm sure sometime later, you'd kick yourself if you started stripping the thing to sell the parts. Can you hear any output in a nearby receiver?

I've got a basket case to revive here, a big project for when I don't have any other distractions. The tx is notorious for being a pain to work on because of its "modular" construction, kinda like 10 lbs. of s#!t in a 5 lb. bag. Just gather all your service info and scour the net for any service info, disassembly, and pics you can find; they'll be helpful. Also, don't dig in until you're 100% ready to do so.   
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Todd, KA1KAQ
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« Reply #5 on: September 26, 2017, 09:05:40 AM »

It sounds like you may not be equipped to repair this beast, Frank - which is fine, the 32V series transmitters are not what you'd call 'easy to service'. The design was probably more on par with the Globe King, size-wise, then re-engineered to fit into a smaller, desk-top cabinet. Ease of access is sacrificed - there are very few areas of this transmitter you can fix easily. Even if it's a simple case of a single component.

I've had mine apart numerous times, actually had a friend fix it once because I couldn't figure it out. Turned out to be the tuning linkage - it had slipped and gone out of sync, so to speak.

There's also an oil-filled cap in back that goes bad. Am trying to remember if loss of grid drive is a symptom. I roached two of them in the span of a couple months, but both times they blew up in use and left an easy trail of oil to follow. One was kind enough to spew its guts out after removing its lid.

As Phil says - don't tackle it until your head is clear and you can focus entirely on the mess ahead of you. Probably true for any piece of gear, but especially so for the maze inside the 32V. I can take several sessions just to disassemble, repair, then reassemble the unit.

If you decide not to pursue it, go with plan B: sell it as-is. You'll get more that way, and have far fewer headaches than trying to strip and sell parts. The few desirable bits would get snapped up first, then you'd be left with the rest.


* 32VBadCap2.JPG (397.24 KB, 1600x1200 - viewed 78 times.)

* 32Voil_spatter.JPG (356.33 KB, 1600x1200 - viewed 50 times.)
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known as The Voice of Vermont in a previous life
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« Reply #6 on: September 26, 2017, 05:46:17 PM »

Frank, check some of the voltages on the buffer and multiplier stages before making any drastic decisions.  These can be checked (CAREFULLY) when the unit is out of the case - the HV interlock will be open but you don't need HV on for these checks.

I have a 32V3 that had identical issues a few years ago.  The rig had been working fine but after a short break I came back and there was zero grid drive.  Everything looked normal, but there was a faint plastic smell in the air.  I opened the RF compartment (on a v3 that is a big job) and visually checked everything but could see no burned or strained components.  However, the 1st multiplier plate voltage was very low.  Schematic shows 1st and 2nd Mult's to have 1K 1W plate resistors but I couldn't find these anywhere. I finally figured out that these resistors are inside the gang-tuned multiplier coil metal cans.  Don't try to open them - its a pain to re-coordinate the gang tuning and almost impossible to drop the RF deck open to remove the coils.  You don't need to - the equivalent end points of the resistor come outside the cans to other components (a choke and a capacitor) and you can connect the replacement across these points.  Still tight, but doable.  Don't try to remove the bad resistor in the can.  If its gone up in value high enough to shut down the stage, it won't have a lot of effect on the new 1K 1W you will install.  By the way, I think the same situation holds true for all the RF stages - there can be a 1K 1W in the plate can of any of the multipliers or buffer.

After doing the above, my grid current rating was closer to spec than it had been for many years.  That resistor must have been drifting high for some time.
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WZ1M
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« Reply #7 on: September 27, 2017, 03:32:36 AM »

The 32V series of transmitters had very poor low voltage transformers. I know, I have wound several of these beauties.
Regards,
Gary
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WD5JKO
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« Reply #8 on: September 27, 2017, 09:08:19 AM »



A useful reference with these rigs:

http://www.qsl.net/wa5bxo/32v3/


Jim
Wd5JKO


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W7NGA
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« Reply #9 on: September 27, 2017, 03:41:13 PM »

I've worked on my 32V-3 extensively .. and found that many of the drive problems are usually traced to the tube socket pins and the occasional cold-solder joint. If you can, try wiggling the tubes in the driver/multiplier section and watch for changes. If you should find a problem, needle-nose pliers can be used to reform the pin connection.

W7NGA  dan
Seaside, Oregon
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KJ4OLL
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« Reply #10 on: October 11, 2017, 06:41:04 PM »

Hi,
Finally finished chain saw work on the yard, giant piles now along the road for pickup.
Now trying to figure out how to troubleshoot this 32V-2.
I tested all the tubes, except for the PA, which my TV-10 would test (Found the Hickok adapter for the 4D32) if the bias pot was working, but the TV-10 is currently un-biased.
The 539B has no provision I can find to test a 4D32.
32v2 symptoms
- has HV
- has LV
- has tiny amount of plate current
- no grid current

Looking at the Collins manual, it says “No one but an authorized and competent service man equipped with proper test facilities should be permitted to service this equipment”

!!!

Section 5.3.3 says “Should the grid drive to the final fall below 5ma on the meter due to change of tubes or aging of components, the transmitter RF circuits should be realigned.”

But before I try any of that, I wanted to learn how to use these tube socket test adapters w/ the HP 410C.
All the notes say is “Phone, no mod, readings taken at the LF end of each band.”

It does not say “Key down” for these measurements, (as it does for testing the PA), so I am assuming these voltages are un-keyed.

So I should just walk the test probe around these test points and compare the voltages to the spec?
Today, received a socket test adapter for Loctal from a seller in Latvia, so now can test the multiplier stages that use Loctals!
73
Frank
KJ4OLL


* Screen Shot 2017-10-11 at 18.29.07.png (135.47 KB, 1133x595 - viewed 21 times.)

* collins32v2test.jpg (2050.64 KB, 2592x1944 - viewed 47 times.)
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