Please help! Pioneer sx-1250 in critical condition. Almost dead

[Jcatsweeney]

Looking for some help here... My SX-1250 is almost dead, When I power on I have illumination lights and that's about it. I'm starting with the AWR 106 power supply assy. I have taken some voltage readings and here is what I currently have.

Pin / Actual / Svc manual says I should have
#1. -66 / -62
#2. 66 / 62
#3. 0 / ground
#4. 0 / 0
#5. 0 / 0
#6. 85 / 85
#7. 23 / 23
#8. 0 / 5.4
#9. 0 / 13.5
#10. -5 / 25
#11. 84 / 65
#12. 0 / ground
#13. -63 / -63
#14. -23 / -25
#15. -86 / -87.5

I am thinking I should start by rebuilding this board. Pins 8 through 11 are obviously incorrect. the board appears to be all original. I'm new to electronics so any help or advice would be appreciated.

Last edited: Today at 10:15 PM

 

[ivandezande]

Agree, rebuilt it before troubleshooting anything, there's a ton that goes wrong on those. Check out some 1250 restore threads on AK. Most transistors, all zeners and caps, and some resistors need to be replaced. And the two trimmers.

 

[mbz]

Q1 looks suspect faulty with c-e short. Do you know how to diode test transistors?

 

[mbz]

Q4 is also suspect, possibly failed open.
Need to diode test all transistors/diodes/zeners on this board.
Q9 or 10 may be open. It's something of a mess. It would help
greatly of you could measure, for each transistor, base voltage
to ground, then repeat for emitter then collector to GND.

 

[Tom B]

Very strange in that you seem to have 3 individual issues on that board. The +65v regulator circuit supplies that +25v. Looks like Q1 is shorted. Thay may fix the +65v and +25v. If you get the +65v working but not the 25v, then look to replace Q8

The +13v missing can be issues with the Q9, Q10, Q11 and or that 6.1v zener diode or R17 is open
The missing 5.4v could be bad Q12 and or Q13, and or open R18 resistor.

And of course all the caps probably should be replaced, but I would suggest getting the supplies running first. There could be issues with the caps, but they probably not causing these 3 power supply issues.

 

[ivandezande]

Stabilizer Board:

Q1: 2SD313: 863-MJE15032G
Q2: 2SC869: 512-KSC2383YTA
Q3: 2SC1318: 512-KSC1845FTA
Q4: 2SC1384: 512-KSC2690AYS
Q5: 2SB507: 863-MJE15033G
Q6: 2SA628A: 512-KSA1013YBU
Q7: 2SA720: 512-KSA992FBU
Q8: 2SA684: 512-KSA1220AYS
Q9: 2SD325: 863-MJE15032G
Q10: 2SC945: 512-KSC2383YTA
Q11: 2SC945: 512-KSC1845FTA
Q12: 2SD325: 863-MJE15032G
Q13: 2SC945: 512-KSC2383YTA

1S2473 to 1N4148
2 1N5252B
1 1N5234B

1 680 Ohm 3W
1 1.5k Ohm 3W
1 100 Ohm 3W

 

[Jcatsweeney]

Q4 is also suspect, possibly failed open.
Need to diode test all transistors/diodes/zeners on this board.
Q9 or 10 may be open. It's something of a mess. It would help
greatly of you could measure, for each transistor, base voltage
to ground, then repeat for emitter then collector to GND.

Thanks for the reply BMZ, I am new to electronics, Looks like I have to remove these transistors to test them correct? I am thinking it's probably not a good idea to learn on such a nice receiver. Is there anybody on here that I can send it to and have it rebuilt? Thx

 

[mbz]

Expecting Q1 to have failed c-e short, this can be tested in circuit.
However there appears to be multiple issues as per @Tom B, this will require some analysis and as you
have already pointed out, the SX-1250 is a nice piece so maybe leave it to a tech, alternatively you can send it to
me (I'll pay postage) and it will be put down humanely in a simple ceremony. Seriously though, I'm sure an AK tech
in the area will chime in shortly.

 

[Watthour]

To maintain full perspective, this same issue is posted here:

http://audiokarma.org/forums/index....50-no-sound-indicator-lamps-tuner-etc.847814/