CR-800 New Woes

cleverdick

Active Member
I've just finished re-capping my PSU board, which I decided to do at the same time as fitting a newly-built RIAA preamp (the original had gone noisy on one channel).

No smoke - so that's good!

What isn't good is that the output muting relay no longer operates. (The coil measures one hundred-and-something Ohms.)

The +12V rail is present and correct, but +12R is sitting at 18.6V - although I did many years ago replace the dial lamps with blue LEDs, so that could be the cause.

So basically, I am suspecting TR725, which may have taken the opportunity to go open-circuit.

Would anyone be so kind as to confirm the type (the schematic is as clear as mud) - or at least the Vce max? I really don't want to have to remove the amp board unless I have to.

What I have noticed, on my travels through this receiver, is that the quality of soldering isn't all that. Plus, a lot of caps are right on the edge for voltage, by design.

(Pioneer scored here with the removeable base-plate.)
 
Update: On a double-diode test, TR725 measures 0.8V across each junction and TR724 about 1V. And to confirm, the relay coil is 160 Ohms.
 
The relay wont operate if there is excessive DC on the speaker line, that's the purpose of the protection circuit.
First check for dc voltage, easiest place are the bias test points on the power amp board.
Left channel, measure between TP3 and GND
Right TP4 and GND
Anything more than a diode drop (+ a bit), say 800mV-1V should be checked

I think the 18.6V MAY be ok, higher voltage because no current draw when relay is not engaged

160ohm relay coil sounds very high, but that's just gut feeling

Did you diode test the transistors in-circuit or remove?

First up, check for Vdc at TP3&4
 
OK, it looks like I've made a wiring error! :yikes:

Anyone got a CR-800 apart right now?

Just want to confirm that the black wire (from ER on the amp board) goes to the ground point that is shared with the earthy side of the green-green TX secondary.

By the way, there is an mistake on the power amp board that is not mine! The silk-screening for Q725 shows the collector and emitter transposed.
.
 
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The relay wont operate if there is excessive DC on the speaker line, that's the purpose of the protection circuit.
First check for dc voltage, easiest place are the bias test points on the power amp board.
Left channel, measure between TP3 and GND
Right TP4 and GND
Anything more than a diode drop (+ a bit), say 800mV-1V should be checked

I think the 18.6V MAY be ok, higher voltage because no current draw when relay is not engaged

160ohm relay coil sounds very high, but that's just gut feeling

Did you diode test the transistors in-circuit or remove?

First up, check for Vdc at TP3&4


Thanks: Transistors checked in-circuit.
 
ER --- Emitter resistor ? If yes. No !!! the emitter resistors are not even close to ground potential.

"ER" is just a notation on the schematic, for what appears to be nothing more than a dirty earth. Nothing to do with any emitter resistors. :)
 
The ER pin on the power amp board appears to be an earth, should be connected to power board, will double check.
However as indicated above, need to tread carefully, don't power on until 100% ok
 
Just want to confirm that the black wire (from ER on the amp board) goes to the ground point that is shared with the earthy side of the green-green TX secondary.
From the scjematic ER looks like an earth, should be secured with the other earths/black wires.
 
The ER pin on the power amp board appears to be an earth, should be connected to power board, will double check.
However as indicated above, need to tread carefully, don't power on until 100% ok
Thats correct..
 
Just getting psychologically prepared for the new big switch-on.

Outside, on an extension cord - observing at a safe distance from inside the garage with ear defenders on.

I shall report back.
 
I've just finished re-capping my PSU board, which I decided to do at the same time as fitting a newly-built RIAA preamp (the original had gone noisy on one channel).

No smoke - so that's good!

What isn't good is that the output muting relay no longer operates. (The coil measures one hundred-and-something Ohms.)

The +12V rail is present and correct, but +12R is sitting at 18.6V - although I did many years ago replace the dial lamps with blue LEDs, so that could be the cause.

So basically, I am suspecting TR725, which may have taken the opportunity to go open-circuit.

Would anyone be so kind as to confirm the type (the schematic is as clear as mud) - or at least the Vce max? I really don't want to have to remove the amp board unless I have to.

What I have noticed, on my travels through this receiver, is that the quality of soldering isn't all that. Plus, a lot of caps are right on the edge for voltage, by design.

(Pioneer scored here with the removeable base-plate.)
I have 20V on +12R before and 17.5V after relay's click.
I still have the left channel missing somewhere on power amp. I have new relay fitted in. I cannot find anything wrong on the main amp. Is it imaginable that the new Pansonic relay is faulty?
 
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