York JCB 863 No Audio

[bozzy]

Hello all

Just for fun, I have dug out my old York JCB 863 that hasn't been powered up since the late 80's.

It appears to transmit (showing expected readings on SWR meter) however it has ZERO RX audio (not the usual quiet audio fault) also in RX mode the signal meter only moves up to 0.5.

I am comparing to a Rotel RVC 240 on the same antenna that shows about 5 on the signal meter with RX noise, also using the same microphone between both sets.

Any pointers please before I start taking it to bits?

Regards
Bozzy

[1968neil]

Assuming you have ruled out a duff microphone.......

Firstly i'd clean the external speaker jack as this is a possible candidate if the rig hasn't been used in a long time.
Failing that check for dry joints on the audio i/c (TA7205AP) and replace the large electrolytic capacitor.

The meter may just need setting up due to the pots getting tarnished over the years.
I'd go thru and clean them all them re-align the radio.

Good luck

Regards
Neil

[bozzy]

Thanks for the reply.

Looks like I made the mistake of jumping in too early and being too technical.

I got hold of the circuit diagram, went right through the IF and FM detector stage to find all was well, the issue was an open circuit speaker FFS!

(quite embarrassed)

What threw myself was comparing the Signal meter reading to a Rotel, which I guess had been tweaked far too much.

Anyway, replaced the speaker, got audio, but when transmitting, told audio was very low, cleaned up RV2 and was good.

Now found that ch38 transmits/receives also on ch40, have double checked the 6 binary BCD levels to the PLL chip on all channels (LC7137), all is correct to input that chip, so guessing I need to replace this chip as not selecting correct channels (LCD is fine).

Also, reports of mains humming when transmitting, I noted someone has been in this radio with a hot poker, will change the ceramic caps around the DC socket that have burnt edges....

Regards
Bozzy

[bozzy]

Almost sorted now.

I ordered an LC7137 on Ebay, very quick delivery, managed to remove the old one without damaging or curling up the PCB tracks, soldered in a 20 pin DIP socket, pressed in the new PLL chip and now transmits correctly on all selected channels.

A couple of more bugs to sort out, but well pleased so far.

Regards
Bozzy

[bigpimp347]

Now found that ch38 transmits/receives also on ch40, have double checked the 6 binary BCD levels to the PLL chip on all channels (LC7137), all is correct to input that chip, so guessing I need to replace this chip as not selecting correct channels (LCD is fine).

this is very often just a damaged track on the channel selector which break due to heavy usage in forty years.

rare for a PLL to be gone. especially one channel.

[bozzy]

There were probably more channels that was wrong as I didn't check all of them initially, I was getting the correct 6 BCD levels to the PLL chip on 38 and 40 so I ruled out the channel selector.

Regards
Bozzy

[warhorse]

Well you could have just kept it simples and wired a speaker up so two wires lose, one wire to 0.volts on cb other by checking audio ic pin for audio rx volume! and turning volume up or down to see if audio ic is good or bad lol