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Pioneer SX-880 Relay Question

willyrover

willyrover

Super Member
I recently picked up a Pioneer SX-880. It's my first vintage Pioneer and so far I love it! :D

My question is about the speaker relay. When I turn it on, the relay engages almost immediately. There is no delay. Is this normal for this receiver? :scratch2:

If not, any suggestions would be great?
 
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willyrover said:
I recently picked up a Pioneer SX-880. It's my first vintage Pioneer and so far I love it! :D

My question is about the speaker relay. When I turn it on, the relay engages almost immediately. There is no delay. Is this normal for this receiver? :scratch2:

If not, any suggestions would be great?
Click to expand...

This receiver uses a pa3004 I.C. as the protection circuit, so the diagnosis is greatly simplified.

There are only 2 (ok three) caps and a transistor in this circuit, in addition to the I.C. , so either a cap had drifted way low in value or the driver transistor for the relay is shorted.

The quickest and easiest way is to replace the 3 caps and the transistor.

The next easiest is to measure the voltage on Q35's pin 3 as the unit powers up, it should register way under 0.6v until several seconds after power up, BUT the Q37 relay driver transistor, if defective could affect that reading.
Q37 is 2sc1885 a NPN, ECB, 150v 50mA .75w 200 MHz to-92 transistor.

A Zetex ZTX694B (NPN, EBC, 120V, 0.5A, 1W, 130MHz) 1.08 ea from mouser will do fine, the lead arrangement is different, so watch it....
Otherwise
Fairchild KSC2310 (NPN, ECB, 200v, 50mA, 0.8w 100 MHz) @ $0.11 part number 512-KSC2310YTA from Mouser will have the same lead arrangement.
The caps are:
10uF part # 140-XRL35V10-RC @ $0.06 ea
33uF part # 140-XRL35V33-RC @ $0.07 ea
47uF part # 140-XRL35V47-RC @ $0.08 ea
all at 35v
select first class mail, and your costs should be under 5 bucks total......

edit: I have sent a copy of the sx-880 service manual to the database.

So, get the manual, you will need it.
 
I replaced Q37 and the three caps and there was no change. The relay still kicks in less than a second after the power is turned on.

Voltage on Pin 3 of Q35 reads 0.635 volts as soon as power is applied.

I guess this means Q35 is bad?
 
I reluctantly agree, there's not much else to go wrong, BUT before you condemn that pa3004 chip, pull Q37 and check the pin 3 voltage of Q35 again, to be sure IT is in control of that pin. With Q37 out, nothing else can influence Q35's pin 3.

also check the other pin's voltages as well, that -7 volts on pin 6 especially.

pins:
1 + 13.5 main power to chip
2 no connection
3 output to drive relay driver transistor, 0v and +0.6v or better..
4 centerpoint and overload sense input, over 0v here shuts OFF relay.
5 ground
6 -7v (I'm not sure if it is a bias voltage or a sense voltage), low current
7 ac voltage sense from power transformer, low current
8 timing capacitor connection, other side of capacitor is grounded

I'll say this in advance, I don't have a PA3004 in the parts pile.

ceitron.com lists them on it's website for 18 bucks each.

IF they have it, at that price, we should be REALLY sure.
 
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