Yamaha CR-600 - no radio

[grandpaslab]

When I got this Yam, it was stuck in protection. I replaced the outputs, 2SC458's, and all the caps on the main amp board and now it's making natural sounds again. Not so much with the radio though: neither AM or FM give anything. Well, FM gives me some background noise when turned up (more than AM, anyway) but I get nothing on either band when I turn the dial.

I wondered if there was something going on with the antenna connections - the antenna wiring looks a little hokey. Anyone know if that's stock? Looks like a DIY balun in there. But when I pulled the coax connection off the FM board and hooked up a crude antenna, I got no change.

I'm pretty sure it's not the selector switch, or FM wouldn't have extra noise. Anybody have any ideas where to look next?

 

[grandpaslab]

Slightly more data: if I power down for a minute, then power on with the selector set to FM, I get about a second of what sounds like FM static. Then it quickly fades out.

 

[grandpaslab]

OK, here's a thought. The outputs were not what was wrong with the power amp, nor were the caps. I did the caps and the outputs first, but it still didn't work. It was after I replaced the 2SC458's that it sprang back to life (like an idiot I did not check them to see which one(s) actually failed).

The tuner section is chock full of 2SC458's! What if some kind of power spike killed the poor defenseless 458's in the protector and the tuner as well?

The receiver does make quite a pop when powered on, and the protection relay engages immediately, no delay. Maybe whatever's causing that situation is related?

EDIT: caveat: I have not set the idle or zeroed out the output. Left my dang MM at work.

 

[avionic]

Before you start pulling the C458's. Check your power sources/supplies for the tuner(s).

Have you recapped the power supply and protect circuit ? Relay driver transistors may be shorted causing immediate relay "click".

 

[avionic]

I wondered if there was something going on with the antenna connections - the antenna wiring looks a little hokey. Anyone know if that's stock?

Looks OEM to me.

 

[avionic]

What if some kind of power spike killed the poor defenseless 458's in the protector and the tuner as well?

Not likely.

 

[avionic]

OK, here's a thought. The outputs were not what was wrong with the power amp, nor were the caps. I did the caps and the outputs first, but it still didn't work. It was after I replaced the 2SC458's that it sprang back to life (like an idiot I did not check them to see which one(s) actually failed).

The tuner section is chock full of 2SC458's! What if some kind of power spike killed the poor defenseless 458's in the protector and the tuner as well?

The receiver does make quite a pop when powered on, and the protection relay engages immediately, no delay. Maybe whatever's causing that situation is related?

EDIT: caveat: I have not set the idle or zeroed out the output. Left my dang MM at work.

The 458's you replaced. What circuit were they in? What TR #'s were they?

 

[grandpaslab]

The 458's I replaced were:
TR707
TR708
TR717
TR718
TR720

I haven't re-capped the power supply yet. 717, 718, 720 all look like they're part of the protection circuit. There's at least one other TR in the circuit (719) that I haven't replaced. I haven't checked voltages on the tuner board, and won't be able to until Monday.

Thanks for your help!

 

[grandpaslab]

Just finally getting back to this after being waylaid by the start of school and the INSANE amount of homework my daughter is suddenly bringing home.

There is indeed trouble on the power supply board. One of the fuse resistors heated up enough to de-solder itself, and none of them measure very close to their original values. Parts on the way, I'll report back when I get them in.

Also, replaced a couple 2SC458 on the power board on general principle.

Love the trick folding case on the Yam!

 

[grandpaslab]

Victory! The frequencies, they do modulate!

I rebuilt the power supply board: new fuse resistors, new caps, new diodes, replaced the 2SC45's with KSC1845s.

Thanks for the help guys.

John

 

[grandpaslab]

Hmmm, culprit maybe? Somebody did a hack job of an LED conversion.

 

[ryuuoh]

That is some poor splicing. Is there any solder in that splice?