Pioneer Tuner/Amp repair [FIXED]

[on4top]

Go a pioneer tuner/amp from a friend with no audio output .
Display lights up fine / tuner ect .. just no sound .
My first observation was  "protection relay is not turning on"
The protection relay seems driven by a DC Detection circuit .
Further investigation seemed that -19V is present on 2 final transistors their Emitor .. Q3 & Q1 .
Q2 & Q4 no dc voltage on Emittor ( wich is ok )
I desoldered all final transistors en checked them .. all fine .

But still on the Emitor connection on the PCB .. stil -19V where Q3 & Q1 use to be soldered on .

Checked most components on the amp section of the pcb .. emitor resistors / drive transitors / diodes  nu luck yet  finding a short transistor or capacitor ?

Service manual / schematic -  http://www.kallhovde.com/pioneer/tricomp/Audio/SX/SX-1300_2300_ARP1477.pdf

[KhronX]

If one channel is ok, you can take comparative voltage readings between the two channels ("good" vs. "bad").

If you've got a negative DC voltage on the output, that would indicate that Q511 and/or Q507 are (nearly) fully on, and pulling the output toward the negative rail.

[richnormand]

Do I assume both channels are same?
There is an overload circuit in the output amp, triggered, does it shut down both channels?
Voltage at collector of output trans?
Main PSU voltages OK to amp section. Look for the big caps and ensure voltage is OK
Multifunction switch OK?
R534 and R533 OK?
Any "hiss" on the output, or any voltage offset or a "thump" when turning on?
If you have a scope can you follow the audio from either the tape or phono input? In particular for audio output from the buffer stage.

SP switch assembly OK?

[KhronX]

If you had read the OP a bit more carefully, and taken a peek at the linked schematic (hint: page 7, middle-bottom), you'll get an easy answer to most of your questions 

1) The -19v is present on only ONE of the amp's two channels (Q1 and Q3 are the output transistors of the bad channel); no DC on channel two (Q2 & Q4)
2) See schematic (hint: yes, both channels go through two contacts of the same relay)
3) Voltages likely ok, but waiting for confirmation
4) Switches unknown
5) Since the relay's open (due to the protection circuitry getting triggered from the -19v on one of the outputs) i'm preeeeeeeeetty sure there's no hiss 

Edit due to edit: Good question about the emitter resistors...

The amps are AC-coupled (through C501 and C502), so whatever's causing that huge DC offset is most definitely restricted to the power amp section itself.

Seems you have a multimeter.
Do I assume both channels are same?
There is an overload circuit in the output amp, triggered, does it shut down both channels?
Main PSU voltages OK to amp section. Look for the big caps and ensure voltage is OK
Multifunction switch OK?
Any "hiss" on the output, or any voltage offset or a "thump" when turning on?
If you have a scope can you follow the audio from either the tape or phono input?

SP switch assembly OK?

[on4top]

Thanks for all reactions !

Tonight i do some more checking .. i would like to find 1 part i can remove so voltage is gone on output .

Then 1 channel should work ( relay should switch on when no DC is present on output )

[KhronX]

Well, if you don't care whether the bad channel gets fixed or not, the only part you'd need to remove is the resistor going from the bad output, to the DC detection circuitry - in this case, R557 (10k).

[mzacharias]

At a glance - I would check IC601, a 78M12  regulator, since you seem to be missing an offsetting positive bias on both channels. Been repairing audio > 35 years.

[KhronX]

The odd thing is, unless i've horribly misunderstood something, that -19v offset is present at only ONE of the two amplifiers' output. 

That kinda makes me doubt the actual issue is common to both channels. But i stand to be corrected, of course

At a glance - I would check IC601, a 78M12  regulator, since you seem to be missing an offsetting positive bias on both channels. Been repairing audio > 35 years.

[mzacharias]

The odd thing is, unless i've horribly misunderstood something, that -19v offset is present at only ONE of the two amplifiers' output. 

That kinda makes me doubt the actual issue is common to both channels. But i stand to be corrected, of course

At a glance - I would check IC601, a 78M12  regulator, since you seem to be missing an offsetting positive bias on both channels. Been repairing audio > 35 years.

Sorry - mis-read your post. Funny thing is - I had a whole list of stuff pertaining to one channel, then ash-canned it when I read your post to mean both channels malfunctioning.

In addition to basic checking transistors, I would check for bad resistors, such as R520 and R522, and if they are good, measure the voltage drop across them in operation. Voltage readings are key to determining which part of the amp circuit is malfunctioning. For example, if Q505 or 506 showed an abnormally high voltage reading across the emitter-base junction, then either that junction is reverse-biased somehow or the junction is open. Likewise - the voltage readings emitter-base of each output transistor may point to which 1/2 of the circuit is malfunctioning (the positive or negative half, that is).

[on4top]

Well, if you don't care whether the bad channel gets fixed or not, the only part you'd need to remove is the resistor going from the bad output, to the DC detection circuitry - in this case, R557 (10k).

Remove  R558 ( 10K ) en yes now  relay is working and we have sound on the  "Right Channel"

Seems the -19V is on Q2 & Q4 and not Q3 & Q1 ... messed up in previous post .

R557 is stil in place so no DC on the Right channel with  Q3 & Q1 i soldered back in place now .

Voltage over  R519 = 0,5 volt   R521 = 0,7 volt   /     R522 = 0,7 volt   R520 = 0,50 volt ..

78M12 is also ok .. 1st thing i checked when i opened  :-)

[oldway]

Check if you don't have a NEGATIVE input voltage on R559.....in this case, C501 would be reverse biased and will leak for sure, applying a negative input voltage to Q501.
All the amplifier would than be OK and this could explain the -19V on the emitters of Q1 and Q3 with all the components checked as OK.

[on4top]

i have 0,9 volt on both  Resistors on the pin connected to C 501 & 502  ( r559 & r560 )

on the other side of resistor i have 6,8 volt ( measured to gnd  )

ps : C501 is the working side for now ..   C502 is the bad side of the amp .

als since i removed the resistor en the relay works . voltage on emittors has going up to  -29V ...


R515 has only 0,05 volt across ..

R516 has  24,5 V across !!  (  non working side )

Q501 & Q515 have an emitor/collector voltage of  +/- 45 volt

Q502 & Q516 have an emitor/collector voltage of  +/- 30 volt .

[mzacharias]

can we get some voltage readings across critical resistors such as R520(R519) R521(R522) R563(R564) etc?

[on4top]

R520 = 0,60V
R519 = 0,56V
R521 = 0,84V
R522 = 0,89V
R563 = 0,934 V
R564 = 0,33 V

[mzacharias]

I would suggest replacing the differential transistor pair on the input portion of that channel.
For confirmation, you can swap the pairs from one channel to the other. If the symptom moves to the other channel, diagnosis is confirmed.

[on4top]

Q501 & Q515  swap with Q502 & 516  right ?

[mzacharias]

Q501 & Q515  swap with Q502 & 516  right ?

Yes - that's them.

[on4top]

done this .. no change .

working channel still works  .

did the same for Q510/Q512 with Q511/Q09.

so all these transistors are fine .

[mzacharias]

Well then try Q505, 506, 507, 508. Next up would be other less likely higher value resistors. There is also a low frequency rolloff capacitor C511 / C512, if I have not already suggested. Leakage here can cause offsets but usually full rail or drifting around in value.

[on4top]

swapping Q507 & Q508 i think did the trick ..

Left channel now seems to work ..
have to unsollder r557 now.. ( to override dc protection ) DC voltage is now on the Right channel ...  with Q507 removed

r558 is back in place .. so dc is gone on the left channel now ..

now source a  2SC2705 or equivalent ...

[KhronX]

http://www.ebay.co.uk/sch/i.html?_from=R40&_sacat=0&_nkw=2SC2705&LH_PrefLoc=3&_sop=15

and/or

http://www.ebay.de/sch/i.html?_from=R40&_sacat=0&_nkw=2SC2705&LH_PrefLoc=3&_sop=15&_clu=2&_fcid=70&_localstpos&_stpos&gbr=1

[on4top]

yep that will probably the simpelst

altough i hate waiting .. want this thing of my workbench before 2017

thanks for al the hints ... now i'm thinking why it's gone bad .. AND when i test on transitor tested it seems ok ..

[mzacharias]

Wish I'd thought exactly of this sooner - I've seen many 2705's and 1145's bad, often noisy, often causing offsets. I used to buy them 10 to 20 at a time.

[on4top]

Yep i  probably wil buy some spares and replace them in both channels .

Transitor tester did say some higher values i compared both of them .. so must me some difference ..

Not easy the find the bad one ...  shorts are easyer

[KhronX]

Perhaps some BD139's might be easier to find locally? They should be "close enough", and are some of the most widespread "medium power" NPN's in Europe, i think

Or maybe MJE340's...