Pioneer SA-8100 protection issue

Philsound

Active Member
Hi, yes, i know, it is a common thread for this amps family but still a real problem.
I've started working on a SA-8100 and then the famous protection bulb shines again! ;-)

I tested the voltage and got :
Protection board : AWM-027, pin 16, very instable and fluctuating around 20V where it should be around 35V.

Check on the power supply board and got the same 20V on pin 19
others checks on power supply board show that except pins 16 and 17 where I found respectively 13V and -13V, all others voltages are at least 10V below the reference.
I've changed Q1 and Q2 with TIP 31C and TIP 32C respectively, no improvement.
I've checked R1 and R2, ok.
I also found around 55V at the base of Q1, where it should be 35.6V

I am blocked now and need some advices from experts to move forward ! :scratch2::scratch2:

Many thanks,
 
Check R9 and R11 (and R10 and R12). The voltage being 13V at the emitter of Q3 doesn't mean Q3 is good...it only means that D9 is working. If you have a multivoltage unit, check that it is set for 120V. Also, all the original caps on this board should be replaced...board gets hot and the originals are all path their prime.
 
I will check them.
But what is surprising me is the fact that the default seems to be symmetric , so my first thoughts went on a common component.
 
Yes I have 0V on pin 2 and 4, or few mV on all pins supposed to be at 0V.
It is a single voltage unit.
Hi inductor, I just try to understand, sorry if you feel that I don't consider the support.
 
Read the voltage ACROSS R1 and R2 to find the current draw, it may be excessive for the power supplies ability to source.

THEN post all the voltages (ground referenced) on the pins of q1, q2, q3, q4

NO CHEATING, MOVE your probe when reading q1 base and q3 collector, and so forth.
 
Hi, i'm back.

I've moved my probe, carefully but moved ;-))
so, these are the results :

R1 : 62.1V both pins
R2 : -63,1V both pins

Q1 :
B : 15V very unstable, fluctuations of at least 5V
C : 51V stable
E : 14V very unstable

Q2 :
B : -15V unstable
C : -52V stable
E : -14V unstable

Q3 :
B : 13.6V stable
C : 14.8V unstable, up to 22V
E : 12.9V stable

Q4 :
B : -13.8 stable
C : -15.5 stable
E : -13.1 stable

thanks for your help!
 
Read the voltage ACROSS R1 and R2 to find the current draw, it may be excessive for the power supplies ability to source.

THEN post all the voltages (ground referenced) on the pins of q1, q2, q3, q4

NO CHEATING, MOVE your probe when reading q1 base and q3 collector, and so forth.

The r1 and r2 voltage readings were NOT (ACROSS)ground based, one DMM lead on EACH side of the resistor.

to find the current draw, it may be excessive for the power supplies ability to source.

also, the voltage on one side of r1 is connected directly to the collector of q1, yet there is a 10 volt difference. This also holds true for the other resistor r2 and Q2's collector)

something very fundamental is happening here.

also have you diode tested q3 and q4 out of circuit? don't do the tests piecemeal, and also do q1 and q2 as well, ALL WITHOUT APPLYING POWER BETWEEN EACH TRANSISTOR'S TEST.
 
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ok Mark, i will check again for R1 and R2.
I have a transistor tester (Peak device), will check Q3 and Q4.
I have replaced Q1 and Q2 2 days back with strong TIP 31C and 32C.
What do you mean by "piecemeal"?
 
pop in a new one and it silently goes POOF before you even get the probe on it. because the problem with the circuit has not been corrected and it takes ANOTHER one out.

Thus test all the transistors in the interconnected circuit at the same time.

test q1 and q3 at the same time or q1, q3, q2, q4 at the same time.
read voltages at q1 and q3 at the same time or q1, q3, q2, q4 at the same time.

never assume that things stay the same, prove they are...
 
Hi Mark,

just had time to test Q3, was good 1 time over the 4 times I tested it with my transistor tester! so i consider it as dead !
Went downtown and found 2SA733 and 2SC945, bought 6 of each.
The funny thing in Africa it that you never know what you can find in these small local shops, some jewels sometimes, sleeping there for decades...!
I will change Q3 and Q4 and retest all the voltages.
Seems consistent?
many thanks,
 
Some news, good and less...
I've changed Q3 and Q4; then, I tried and....the magic clic happens!!

I thought it was the end of the story but...I realized that a small wire from the power board leadind to the pin 15 on the amp board was disconnected, cause it was too short when I replaced Q3 and Q4.
I reconnected it and then, no more clic.
I've checked all 4 outputs and they are fine.
Just had time to test and find out that both the drivers and the output on the right channel where not powered, except their collector if I remember well.
So I think that one, or many of the small Q2, Q4, etc are the culprits.
Don't have time to test further today, I will do it tomorrow and will try to find some spares.
Thanks,
 
If i get it working (and it will !), the next step will be the adjustment procedure I guess.
I have a SM for SA 7100 and SA 9100 but only the shematics for the 8100.
Could you please tell me how to do it? the amp board looks similar with the 7100 but not the same pins...
Thanks,
 
Some news, good and less...
I've changed Q3 and Q4; then, I tried and....the magic clic happens!!

I thought it was the end of the story but...I realized that a small wire from the power board leadind to the pin 15 on the amp board was disconnected, cause it was too short when I replaced Q3 and Q4.
I reconnected it and then, no more clic.
Now that you have replaced the parts on the power supply, how about confirming that ALL the voltages on that board are all present and accounted for?
 
Sorry, you are 100% right!
I have checked them all and they are now all at the nominal values and very stable.
Thanks again
 
If i get it working (and it will !), the next step will be the adjustment procedure I guess.
I have a SM for SA 7100 and SA 9100 but only the shematics for the 8100.
Could you please tell me how to do it? the amp board looks similar with the 7100 but not the same pins...
Thanks,

here is a service manual for the sa-8100, it is 90 meg and I confirmed the presence of the adjustment procedures

I will give a bare bones outline:

Vr1, Vr2 to center (DC offset adjust)
Vr3, Vr4 CCW (anti-clockwise)

zero volume,
edit - IGNORE the stupid 4.7k resistor instructions
no speaker loads

Vr1 pin 3 to ground 0.000v (+/- 20mV)
Vr2 pin 23 to ground 0.000v (+/- 20mV)

vr3 pins 1 & 2 20mV
vr4 pins 24 & 25 20mV
 
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Great ! Thanks a lot.
When they say in the SM "terminate input terminals with a 4.7Kohm", what does it mean exactly? Do i have to connect a resistor somewhere between 2 pins?
Should I first remove the wires from the pins 24 and 25 if any?

It will be the first time that i will do an alignment procedure on a Pioneer amp; I did it on Sony and Sansui a couple of times but never Pioneer.
This 7100, 8100, 9100 are really nice amps but very sensitive and not easy to work in, in my opinion (btw, some old Sony like TA 1120 are worse..!).

They need to be treated by expert hands, which is not my case ! ;-)
 
I was too optimistic...
After changing all small transistor on the right channel on the power amp board, the relay did not work.
I compared the 2 channels and the realized that I don't have any voltage on pin 23 on the amp board, nor on pin3 and 4 on the protection board.
I started to check the way of the 34v that is present on pin 16 (protection board), and found that after R14, I still have 34V but after R13, I only get 3.7V!!!
I've removed the resistor and they are both ok at15k....
I am lost again ...
 
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