TRC-57 restoration

[TM86]

New year, new project.

TRC-57. Cosmetically really good. Electrically questionable. Someone has rebuilt the power supply using a different transformer and diode arrangement than stock. That bit seems to work, though. But for some reason they decided to route the new AC wires through a hole with no grommet when there's an unused grommet right next to it. On/Off switch is gone and wired around. Clock doesn't work. No RX or TX. Fuse holder is the screw on cap type, and the cap's gone. Fortunately I have one of those.

Oh, and for some reason at some point the screws that hold the PLL can in place were glued/epoxied. As in at least two different adhesives were applied. Couple of minutes with some side cutters to fracture the crud and a dental pick to pull it out of the screw heads fixed that right up.

Surprisingly even though the PLL can looks like it's been in and out of this radio a few times, I don't yet see any evidence of a channel modification ever being done.

I think the first step will be to locate a replacement Volume/On/Off control. Any suggestions on where to find that will be appreciated. 10K dual ganged pot with on/off switch, splined shaft about 15mm or a half inch long, depending on if you use metric or freedom units.

I am, of course, off to search Mouser, DigiKey, Barkett, etc.

 

[TM86]

Never mind, found one. Wasn't cheap, but it's on the way.

 

[TM86]

VR7 fell apart, yay.

Something is not quite right in the PLL. Someone had taken the 5 Volts meant for the channel selector and connected it to Test Point 3, which is the active filter output and the input to the VCO's varactor. So now I'm wondering if something fried in there or if it's a problem with one of the divider chips. The VCO is free running at about 18 MHz, so at least the oscillator part is still working.

Hoping I won't have to yank the metal can the VCO lives in, betting that I probably will.

Maybe I should have just joined the "Beer of the Month" club.

 

[TM86]

Crud. Was looking at the wrong test point. VCO is not VCO'ing. Well, this should be fun.

Going to see if I can tear into the can and not destroy it in the process.

 

[TM86]

Nope. VCO is f*****d.

As you can see the whole thing is potted in some kind of epoxy or resin. Probably for thermal stability. Or just to be a-holes. But certainly one of those.

So now I need to come up with an alternate plan.

Definitely should have joined the "Beer of the Month" club.

 

[brandon7861]

May not be the same VCO, but I think there is a lot of relevant info in this video. Good luck!!!

 

[TM86]

May not be the same VCO, but I think there is a lot of relevant info in this video. Good luck!!!

I could actually build a replacement on perf board.

Thanks to the magic of the really strong flashlight I can see far enough into the epoxy to tell that they used a 2SK19 for the oscillator transistor. Every other part is documented in the Sam's schematic so I do have BOM on what to order.

20 discrete components stuffed into a 7/16" x 1 7/16" footprint. What could possibly go wrong?

If that doesn't work I can always throw together a Si5351 VFO solution.

 

[Lkaskel]

There is a guy on FB that sells updated VCO's. Look up Razor Radios. He is a VERY good guy. I am unsure if he has one for your radio as I have only used ones for the Cybernet boards.

 

[TM86]

There is a guy on FB that sells updated VCO's. Look up Razor Radios. He is a VERY good guy. I am unsure if he has one for your radio as I have only used ones for the Cybernet boards.

I can ask. For Cybernet VCO's there's a few choices. Razor, Microchipz, and Spectrum are the first ones to come to mind.

 

[brandon7861]

Can you post the schematic of the VCO? Just curious, I don't see it in the factory manual.

edited pll to vco lol

 

[TM86]

Can you post the schematic of the VCO? Just curious, I don't see it in the factory manual.

edited pll to vco lol

Here's what I have. Sorry about the blurriness where it crosses the page boundary.

 

[brandon7861]

Let me know if you cannot find one because I would be willing to try making one out of smd parts.

I think I have parts that are close enough to work already. I have BB175x varactors which are reasonably close to the 1s2688/BA102, I have BC848's which should work just as well as the 945's in the active filter, and I have J310's which I think should work where the 2sk19 is. I would need to know the footprint with the pin locations. Looks like that external coil would be about 1uH.

 

[TM86]

Let me know if you cannot find one because I would be willing to try making one out of smd parts.

I think I have parts that are close enough to work already. I have BB175x varactors which are reasonably close to the 1s2688/BA102, I have BC848's which should work just as well as the 945's in the active filter, and I have J310's which I think should work where the 2sk19 is. I would need to know the footprint with the pin locations. Looks like that external coil would be about 1uH.

Thanks for that.

So far I've had zero luck locating a replacement. I've started writing code for replacing the PLL circuit (dividers, VCO, etc) with a Si5351. If you can build a VCO out of your parts bin I'd rather do that. Mainly because I'm lazy.

Overall footprint is 36.85 mm by 23.56 mm. Metal shield is about 1 mm thick, with leads about 3.25 mm in from that in all directions.

I've attached two pdf's. One shows measurements between the pins for spacing. These are all approximations. The other shows what components each pin connects to.

If you want the original VCO can for exact measurements I can send that, just DM the relevant mailing info to me.

 

[brandon7861]

The pin locations, is that the pin side going into the main board or the parts side? Am I looking down at the top of the VCO board in that pic?

 

[TM86]

Looking at the bottom of the VCO.