Realistic TRC-458 Problems

[skeeters]

I picked up a pristine unmodified 458 about 10 years ago and was put in the closet until recently. I was looking at doing a recap but decided to power it up to check things out. It powered right up and the receive worked great but no modulation on transmit but had carrier. Also no output on sideband.

I plugged a external speaker into the PA output jack. When I keyed up and spoke, there was plenty of audio coming from the external speaker. I looked at a schematic and determined that since I had audio from the PA output which came from the modulation transformer which is driven by IC4 which is drivin by IC3, both seemed to be ok.

Since I have carrier then TR25 is providing voltage to the collectors of the driver and final. Something is attenuating the audio to IC4 when I put PA switch back to normal/tx mode.

Any ideas folks? Any help would be appreciated as I really want to get this radio back on the air. Cosmetically it is perfect.

 

[loosecannon]

a good place to start is to clean all the contacts on the pots and switches.

then using the service manual start checking the voltages of the IC chips, and after that the associated transistors.

If you find a voltage that doesn't jive with the manual, that's the place to start looking for a faulty component.

I will tell you that i wouldn't even take a radio that old in for repair unless the owner agreed to do a re-cap, and i would do the re-cap first.
it's a lot faster than troubleshooting usually.
LC

 

[skeeters]

a good place to start is to clean all the contacts on the pots and switches.

then using the service manual start checking the voltages of the IC chips, and after that the associated transistors.

If you find a voltage that doesn't jive with the manual, that's the place to start looking for a faulty component.

I will tell you that i wouldn't even take a radio that old in for repair unless the owner agreed to do a re-cap, and i would do the re-cap first.
it's a lot faster than troubleshooting usually.
LC

Agree and a recap is absolutely needed. I have access to a scope from work to do some troubleshooting but my eye site is getting bad.

I would really like to find someone, who is competent, to recap, repair and align the radio. I have tried getting in touch with Mike who I have spoken to in the past about another issue, but it goes straight to a full voicemail box. I also see he hasn't updated his youtube channel in several years.

Any suggestions?

 

[nomadradio]

Hmm. Mike audio from PA, but not from AM or SSB transmit?
I tend to revert to the TRC-449 schematic. The scan posted here came out really clear. https://cbtricks.org/radios/realistic/trc_449/

The mike audio splits off to the PA just ahead of TR20. D21 and D22 can stop the show if they lose circuit current.

A 'scope would be the ideal tool to follow the audio from IC3 pin 6 to the emitter of TR20. Has to be stopping somewhere around there.

73