Junker 858 Madison

[TM86]

Since my last project didn't go anywhere near what I planned, I've decided to put that on the shelf for a little (or long) while and take on something else.

President Madison basket case I bought off fleaBay a few years ago. 858 chassis.

It has a few problems. Clock doesn't work. No receive audio or AM transmit audio because somebody yanked the audio amp chip, L10, and L11. Clarifier was modded, and now doesn't work. The SWR/MOD meter is stuck. And of course there's glue and old caps to deal with as well as dead or missing light bulbs. Oh, and a few holes in the case from where various channel mods have been installed and removed over the years. I'm just glad they didn't drill holes in the face of the radio.

The good news? It does transmit in all modes, and not too far off frequency despite the clarifier issue. Channel switch seems to work. No dead segments in the channel display.

I'm hoping to do a straight clean up and restore on this one. Created this thread so I could ask all my dumb questions in one place. Hopefully it provides some entertainment.

I will be stealing some parts from a Cobra 138 XLR that's in even worse shape, but does have the parts I need. Unless they're busted in that radio.

 

[nomadradio]

Just make sure you change the output capacitor on the audio chip. If it fails, it can take the uPC1156 with it, along with the voice coil in the speaker.

73

 

[TM86]

Found something... different. Where L10 and L11 had been yanked, someone bridged a small ceramic capacitor across the gap. Which, looking at the schematic, explains why I still have sideband TX audio. Not sure why this mod was done, but it doesn't block audio from getting through so I'll leave it alone for now.

Also found two 420 Ohm resistors stacked in parallel in the power supply where R305 should be. I'm guessing the original got a little crispy. Going to order a 220 Ohm replacement, and go overkill on wattage.

Recapping and glue removal underway. Cleaning out the fuzzy dust monsters as I go.

I did find that I have a upc1156 in my parts stash, now I just need to find some nylon screws and a sheet of sil-pad material.

 

[Klondike Mike]

I was not in agreeance with your last project but I was impressed with your attempt. The experience you gained was just a stepping stone to your next project success. Good luck with this one.

 

[TM86]

I was not in agreeance with your last project but I was impressed with your attempt. The experience you gained was just a stepping stone to your next project success. Good luck with this one.

No worries. My hare brained ideas won't be to everyone's liking. Thanks for the well wishes.

BTW, any plans to sell Sil-Pad kits?

 

[Klondike Mike]

... BTW, any plans to sell Sil-Pad kits?

Nope. Never crossed my mind before. Maybe. What was your last order and how much did you have to pay?

 

[TM86]

Nope. Never crossed my mind before. Maybe. What was your last order and how much did you have to pay?

For Sil-Pads I bought a bag of 100 TO-220 insulators off fleaBay for about 5 bucks. Which is great for final, driver, AM regulator, etc. Not so useful for the audio amp chip. I'll probably have to get a sheet of the material and cut it to size.

 

[loosecannon]

TM86,

that mod where they remove L10 and L11 is an old audio mod from the secret CB days and it bypasses the low pass filter in the radio.
it made the radios swing to higher wattages but eliminated the cool compressor that was built into this chassis.

unless you have a parts board, you're going to have a hard time finding replacements for them.
LC

 

[TM86]

TM86,

that mod where they remove L10 and L11 is an old audio mod from the secret CB days and it bypasses the low pass filter in the radio.
it made the radios swing to higher wattages but eliminated the cool compressor that was built into this chassis.

unless you have a parts board, you're going to have a hard time finding replacements for them.
LC

Thanks for the info. Wasn't aware of this mod. I've got a Cobra 138 XLR I can steal parts from. I'll have to take a closer look at that part of the board to see if anything else got yanked that might be needed.

 

[Klondike Mike]

... For Sil-Pads I bought a bag of 100 TO-220 insulators off fleaBay for about 5 bucks.

I'm already in the hole for -$50 for spending time thinking/researching this. No profits to be made here. No thanks.

 

[TM86]

Good call, LC. Looking around where L10 and L11 were, C72, C73, C74, and C75 have all been clipped out. Fortunately I've got some leftovers from some other projects that'll work as replacements. Also, looks like I might be able to grab replacement inductors from Mouser for L10 and L11.

 

[loosecannon]

good deal.
please post the part numbers you used if they end up working.

you should also check out D21 and D22. these were also common mods and you might find them jumped out or with a resistor between them.
LC

 

[TM86]

good deal.
please post the part numbers you used if they end up working.

you should also check out D21 and D22. these were also common mods and you might find them jumped out or with a resistor between them.
LC

Yeah, they dropped a big blob of solder across those two. Desoldering gun cleared that right up.

Recap is mostly done. Have to order a power supply filter cap, didn't happen to have one laying around.

Currently working through glue removal. Had to replace TR402 and TR403. The glue used to hold the plastic sleeves for the leads in place had turned the leads green all the way to the body of the transistors. They still work, but for how much longer?

Not looking forward to degluing the toroids. They're a pain to get back in.

Hoping to get to pulling the clock apart this weekend and see if it's really a dead motor or just bad gears.

 

[TM86]

Toroids went faster than expected, so I tore into the clock. Motor works, teeth on the first gear are trashed. Emailed the guy that sells Intermatic gears, 'cause that's what his website said to do for this type of motor (WG6B9A). We'll see what he has to say about it.

Anyone know if the nylon screws for the audio amp chip are M3 sized? I've had to scavenge these in the past and while I can steal them out of the 138 XLR I've got here, I'd rather just have a bunch on hand.

 

[nomadradio]

nylon screws

Found 3mm plastic screws on fleabay. The thread pitch is 0.1mm.

Good luck with the motor. They have so little torque that it's hard to judge how well you have freed it up with cleaning and/or lubrication. Takes really low-viscosity oil, I was told.

Never had the patience to rehab those clock motors after the first few tries.

73