Resurecting a TRC 457

[Mork]

Hi Folks,

I recently aquired a TRC457 in great condition but not in working order.

The old man I got it from bought it new in 1978 and used it up to 8 years ago when it just would not come on one day and he stored it under his bed.

The radio had never had the back off it so I know where I am starting from.

The power supply was dead which I have repaired (regulator). Now the radio comes on, but will not TX or RX on either AM or SSB. The internal relay clicks when the mic is keyed and the meter changes color as it is suppose to but there is no power output nor is there any receive. The audio amplifier appears to be working as you turn up the volume you can hear the increase in power to the speaker and the PA is working well.

Any ideas as to where to go from here?

Thanks for any help.

Jim

[Rick]

Check TR24, and is the dimmer working?
Have you tried the radio on ext power supply?

[Mork]

Hi Rick,

I am currently at work. I will have a look when I get off this evening.
Thanks a bunch.

Jim

[Mork]

Also, I forgot to mention, there is a grey wire connected to the PC board next to R29 The other end of this wire has become disconnected and I can't tell where it goes. Anyone have a 457 that they could look at and tell me where this wire connects to? A pic would be perfect.

Thanks

Jim

[Mork]

Rick,

TR24 and TR36 (regulators?) check out fine.

TR43 (Driver) and TR44 (Final) Check out fine.

TR25 also checks out fine.

When you speak of the dimmer are you refering to VR17?

All the LED's are working and the channel selector changes the channel numbers but no RX and no TX.

Jim

[Rick]

So did you try the radio on ext power supply?

What is the voltage at the base, collector, emitter of TR24?

What is the voltage at Pin 12 of the PLL (uPD858).

Is the voltage at TP12 or Pin 11 of the PLL when you change channel? and what is the voltage on channel 1? and channel 40?

The Gray wire problem, Where is one end soldered to?

[Mork]

Rick,

I tried an external power supply with no difference.

I will check the pin voltages when I get home.

The gray wire is soldered down through to the top (NOT FOIL SIDE) of the PC board Right next to R29. It then feeds through the bundled harness and comes out near the front right part of the board near where the thin channel selector ribbon cable connects. This is the end that is disconnected.

If you could drop me an email I will send you a pic of this Rick.

jamesm@nl.rogers.com

Thanks

Jim

[Mork]

Rick,

The voltage on pin11 of the PLL on

Channel 1 is .048V
2 is 4.77V
3 is 4.77V
4 is .051V
5 is 4.77V
40 is .053V

Also the Voltages on T24 are as follows:

Base .052V
Collector .052V
Emitter .084V


Jim

[Rick]

What is the voltage at the base, collector, emitter of TR24 in TX?

What is the voltage at Pin 12 of the PLL (uPD858).

I do not thank you are testing the on Pin 11 of the PLL., if you are then you have a bad PLL IC. To help you ID the right Pin in is connected to the collector of TR31 and the junction of R139.

[Mork]

Rick,

TR24 shows when TX:

Base 9.15V
Collector 12.4V
Emmitter 8.45V

Pin 11 on the PLL shows 2V
Pin 12 on the PLL shows 4.77V

I have sent you a pic for reference.

Thanks

Jim

[Rick]

As I did not get the right response from you, I cannot help you with this fault anymore. I assume this is now closed.

[Mork]

Rick,

I thought what I had sent was what you asked for.
Sorry.
Thanks for all your help.

Jim