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Author Topic: Restringing the band switch on Johnson 500  (Read 15123 times)
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n2len
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« on: November 12, 2009, 11:23:30 AM »

Hello everyone...

I just received my Johnson 500. It survived the trip from Texas to NY.

However, when the tubes were packaged, wrapped in bubblewrap then placed back into the transmitter, the bubblewrap was pushed up against the bandswitch and the cables slipped off the bandswitch pulleys. I checked the manual and see the diagram to re-wrap...


Question?
I am I correct to assume that the enitre front panel needs to be removed to re-string?
Is there any source of front panel disassembly on the net or documents floating around?
Anything to watch out for, and any preventative maintenance that should be done if I do need to remove the panel...

Warm Regards,
Len N2LEN


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WV Hoopie
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« Reply #1 on: November 12, 2009, 12:31:26 PM »

Len,

BAMA has the operation manual! On one of the pages there is a diagram of how that band switch & stuff (string) is positioned. Since it was more than lilkely in the correct position before shipping, I'd try to get it back in place without taking the front panel off. Might have to make sure the band switch and VFO linkage is correct while restringing.

I've never had the panels off of my Ranger or 500 and rather not go thru the pain! The coupling between the VFO knob and shaft has been known to cause grey hair and/or loss of the same.

For years, the search for an assembly manual or document on the 500 assembly has been a failure here. I did locate a ham that indeed had or has a 500 still unassembled in the box! He wanted $15K for the TX and didn't want to even open or look for the assembly info.

So, if there is a lurker out there with those pages....................I'd like a peek.

Craig,
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kg8lb
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« Reply #2 on: November 12, 2009, 02:00:36 PM »

 Not really all that difficult to get the VFO drive and faceplate off of a Johnson..if you have too. The directions in the manual are pretty complete as to re-alignment.

  However, with a bit of ingenuity , some wire hooks etc, you should be able to re-wrap the cord and find you are pretty darn close.
   If you don't have the manual I can probably scan and forward the info for you.
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n2len
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« Reply #3 on: November 12, 2009, 02:04:59 PM »

Thanks for the replies...

I do have the owners manual and see the detailed picture of the winding...The problem is resetting the cord spings onto the back of the bandswitch pulleys. They mount and face the back of the front panel..

I will take another closer look at it...

Len
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n2len
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« Reply #4 on: November 12, 2009, 04:04:58 PM »

I just took a closer look at the bandswitch pulley..

It would be much easier to re-wire with the removal of the front panel.

It would give me complete access to the front of the bandswitch pulley.

What underlying work is involved in the removal of the front panel?

Desoldering involved?

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Roy K8VWX
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« Reply #5 on: November 12, 2009, 04:47:53 PM »

    I remember a long time ago I restrung the 500 band switch and it was a SOB. The way the manual showed it would not work for me. I think I removed the meters before i started dropping the panel. LOL  Angry 
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kg8lb
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« Reply #6 on: November 12, 2009, 06:22:05 PM »

   All the knobs need to come off, disconnect the meters and you may leave them mounted. The VFO dial escutcheon is retained by the pilot lamp bushings VIA the nuts on the inside. As I recall you may be able to release the coupler's set screws behind the panel or remove the pointer and disassemble the VFO drive from the front. It should be obvious which way is easiest by the time you get that far along. It was 1994 when I had mine apart but it really was not that bad a job. Take your time and enjoy the "experience"

  BTW, Is this the same 500 that was just on QTH a few weeks ago ?
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n2len
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« Reply #7 on: November 12, 2009, 09:13:29 PM »

Thanks Gary,

I removed the knobs, nuts, washers...

I will now remove the wiring from the meters....

<snip>
The VFO dial escutcheon is retained by the pilot lamp bushings VIA the nuts on the inside. As I recall you may be able to release the coupler's set screws behind the panel or remove the pointer and disassemble the VFO drive from the front.
<unsnip>

How do I remove these pilot lamp bushings? Just simply unscrew the nuts from the top of them?
There are also 2 small nuts on the front of the escutcheon, they were hidden under the "drive" and "tune/operate" switch...

Pictures provided...

Len



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n2len
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« Reply #8 on: November 12, 2009, 09:53:13 PM »

Removed just about everything except the key switch...

Looks like you need a very thin wrench to get to the inner nut...

Maybe a needle nose....


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WV Hoopie
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« Reply #9 on: November 13, 2009, 01:09:30 AM »

Removed just about everything except the key switch...

Looks like you need a very thin wrench to get to the inner nut...

Maybe a needle nose....

needle nose will buggar up the nut or panel. Gonna need an old wrench and a grinding wheel, maybe a dremel tool to shape a wrench to fit the inner nut. my 500 didn't have a key or the three cables. i removed the switch with a homebrew wrench and made a key. later found a new switch & key, keeping the switch for a spare.

craig,
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n2bc
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« Reply #10 on: November 13, 2009, 08:14:57 AM »

I've done a couple Rangers and a Valiant...  Be careful of the flexible drive on the VFO shaft.  Pull the panel STRAIGHT away from the chassis.  The drive is made of thin phenolic and quite brittle.
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n2len
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« Reply #11 on: November 13, 2009, 08:52:06 AM »

A bunch of great guys here!

Thanks for all replies...The front panel has been totally removed. Meters still attached to the panel. I was able to re-string the bandswitch pully in 2 minutes.
However, I am not sure if I have a further problem.
After re-stringing, I tested the bandswitch for movement and control.
The switch and pully worked however, it would not complete it's full range
of 5 band positions without stopping. The string will then fall off a samll lower idler pully. I looked at the bottom of the cabinet and noticed that the large pully when turning has 2 rather large teeth that when in the correct position, slide into a square device. I believe that this device also moves...
It was too late at night for further troubleshooting and need to shoot some pictures and look at the manual for the part name.
Thinking about it now, I am unsure if I had the upper bandswitch in the correct starting band position as the lower so they would track together while turning the bandswitch. However, I do remember when I began to re-string the pully cable I had to turn the bandswitch several clicks so the cable would fit and have the correct slack. I would think that if I have the lower pully in the 80 meter position and the upper bandswitch in the 80 slot the cable should fit.
But I don't think this was the case. I seemed that the cable would re-string only one way.
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Rob K2CU
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« Reply #12 on: November 13, 2009, 09:46:52 AM »

IF the square device you mention is under the VFo, it is the VFO band switch linkage and easily hung up as it has to interact with the "teeth" driven by the bandswitch shaft. the VFo switch, at least on a Valiant, selects 160/80, 40/20/15/10, or 11 meters. as long as it works for the first two positions, who cares if it doesn't do 11?

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n2len
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« Reply #13 on: November 13, 2009, 12:51:51 PM »

Rob,

Thanks for the reply...I re-wired the pully again in the 80 meter position.

Regarding the VFO linkage. I am not quite sure at what point (band) do the teeth engage with it. It seems like it hangs up on it. The teeth want to pass through it but either miss the slit etc... or its not moving freely (linkage part).

Thus making the wire hang up and fall off the lower idler pully.
The cabling seems tight enough for the functionality on the pully.

Is there a way to lubricate the linkage and how to get to it?

Pictures....

Len


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n2bc
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« Reply #14 on: November 13, 2009, 01:16:45 PM »

Loosen the gizmo with the engaging pin and slide it out of the block.  Now see if the block rotates easily.  I had a Ranger where the shaft was seized to the switch body. Ended up replacing the entire switch, no fun.  If it will move, but with difficulty, a smal amount of penetrating lube may do the trick.  Remove the block to get at the end of the shaft.

I'm imagining the fun it must be to roll the 500 around on your bench!  It will need to be upside down to lube the switch the 'easy way'.  The hard way is to completely remove the VFO box.  You may need to do that anyway... I suspect the 500 suffers from the same poor design of all the other Johnson VFOs, with the VFO screen regulator inside the box frying away everything around it.  Lots of posts on moving the regulator out of the VFO box.
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n2len
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« Reply #15 on: November 13, 2009, 03:15:04 PM »

Using 2 fingers I am able to move the block and turn the shaft back and forth. However it dosent move freely. Actually it is quite difficult to move. I will remove the set screw and slide off the block. Then some penetrating oil on the end of the shaft and re-install the block. Hopefully it will work to loosen it up a bit.

Regarding the 500 on my work bench...
The 500 was delivered to me wednesday afternoon. It never actually made it to the back room work bench. It is on my AM radio desk which I guess now can be considered my 500 ONLY temporary work bench...

I really shouldn't be working on my radio desk...

Len


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KC2IFR
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« Reply #16 on: November 13, 2009, 04:04:50 PM »

Len,
As u probably have found out.......before u re-string it.........make sure all components the sting has to move are working properly ALONE. The vfo can be a problem but not insurmountable.  Take your time and check everything one at a time. My 500 works great but u have to stay on top of these old mechanical parts!

Bill
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WQ9E
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« Reply #17 on: November 13, 2009, 04:14:37 PM »

A trick I have used to free up shafts is to apply some heat from a soldering iron and then flow some oil into the area while it cools.  You don't want to get the shaft terribly hot since you don't need it hot enough to melt solder!
This has worked for me on numerous radios that had switch and pot shafts that were difficult to turn.

The RF deck of the 500 isn't too bad to work on since it is pretty light; the poorly balanced power supply/modulator can be a pain.  My only objection to my 500 is that for what the 500 sold for they could have at least printed a custom VFO dial without the 160 meter calibration-of course actually covering 160 would have been even better!

Rodger WQ9E
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n2len
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« Reply #18 on: November 13, 2009, 04:28:59 PM »

Thanks for all the replies...

I will take the suggestion and apply tonight at the SHAFT!

What is everyone take on Dexoit and Gold for potentiometers?

Any other suggestions for usage on switch contact (mode etc...) than taper controls like mic gain etc...
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KC2IFR
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« Reply #19 on: November 13, 2009, 04:32:20 PM »

The 500 rf deck is well built but as Rodger said the PS /modulator can be a problem. I have rebuilt mine heavily!
New mod iron and a big a$$ plate transformer. The 811's were replaced with 572B's and I use home brew cathode followers to drive the 572B's.
This is a pic of the cathode followers on a separate chassis.
Sorry about the dust!!!!!!

Bill


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KC2IFR
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« Reply #20 on: November 13, 2009, 04:33:37 PM »

Next picture.................obviously this is PS/modulator.....

Bill


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n2len
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« Reply #21 on: November 13, 2009, 10:15:32 PM »

Very nice...! Supply and HV

Here is the bottom of my 500...Another project will be to change out caps...

It appears bone stock....


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kg8lb
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« Reply #22 on: November 13, 2009, 10:20:04 PM »

Ah yes, the pesky little key switch...forgot all about that little rascal . Used an old "Bonney" tappet wrench . Ultra thin and just the ticket. Looks like you have it about done now. Good on ya!
  We'll keep an ear out for the new 500 .
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N3DRB The Derb
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« Reply #23 on: November 14, 2009, 06:02:53 AM »

Congrats on making it good. You'll be quite strapping with a good antenna.  Cheesy
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KC2IFR
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« Reply #24 on: November 14, 2009, 06:11:42 AM »

Len,
That thing looks like its brand new.
Me thinks u have a winner! Hope to work ya one day soon!

Bill
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