Pioneer SA-8100 protection issue

[Dingman]

what is the emitter voltage of q4? 13v or 0v.

0v means zener is probably dead, or q4 is dead and not feeding the -13v zener.

I must inject some discipline to this free range thread.

post arm-030 voltages at pins 9,19,18,17,16,11,15,14,13,12,4 & 5

if pin 12 is not within 10 % of -42 volts, post voltage readings of q2 and q4.

Thanks for showing up, I was beginning to think I was on my own. LOL, yes, free range is what you get with lack of direction.

Possibly you didn't look at the picture (and I don't blame you, you may prefer just text numbers, easier to read) - but on that picture you can see that:

Q4 Emitter = 0 volts
Q4 Collector = -8.5
Q4 Base = -0.6

Q2 Emitter = -4.6 volts
Q2 Collector = -48.6
Q2 Base = -8.5

AWR-030: All measurements to ground
Pin 09: 48.9
Pin 19: 35.3
Pin 17: 29.0
Pin 16: 13.7
Pin 15: 0.0
Pin 14: 3.47
Pin 13: 6.93
Pin 12: -4.58
Pin 04: -36.8
Pin 05: 37.0

It's my opinion that Q4 is in need of replacement but that board is darn hard to get to the back, so that's why I've asked if you think I'm in the right spot.

Now, what I did expect from you Mark, was some significant chastisement for not draining the caps before re-assembly - which resulted in this damage! I have built "cap discharge" set of clips\resistor so that won't happen again. I *thought* the circuits had discharge circuits built in discharge - apparently not!

 

[markthefixer]

It is unavoidable that you will HAVE to access the back of that board. PERIOD.

Q4 emitter IS pin 15, both are at 0 volts, and should be -13v.

Either pin 15 is shorted, C13 shorted or D10 has been destroyed.

Then there's Q4 and Q2. Both have questionable voltage levels.

Quite frankly, rather than fiddling around for days trying to save inexpensive components, a fresh shuffle of zener diode and 2 transistors is indicated, assuming the caps are new. If not, new caps too, especially if the backside is difficult to access, the shipping probably rivals the cost of all new components (excluding most of the resistors).

 

[Dingman]

Thanks, good to know I was in the right area.

I'll get on it pronto! Which means it will be a couple of weeks, LOL.

 

[Dingman]

It is unavoidable that you will HAVE to access the back of that board. PERIOD.
Q4 emitter IS pin 15, both are at 0 volts, and should be -13v.
Either pin 15 is shorted, C13 shorted or D10 has been destroyed.

Then there's Q4 and Q2. Both have questionable voltage levels.

Quite frankly, rather than fiddling around for days trying to save inexpensive components, a fresh shuffle of zener diode and 2 transistors is indicated, assuming the caps are new. If not, new caps too, especially if the backside is difficult to access, the shipping probably rivals the cost of all new components (excluding most of the resistors).

I'm doing the shuffle! skippity do..dah!

Carefully got that board twisted up so I can get at the back.
I have all the transistors swapped, most of the caps and one D10 out - D10 is open both ways, that's where the short was coming from.

Found this...

Echowars can be relied upon to have discussed the matter earlier:

The zeners are standard stuff...a WZ-140 is a 500mW 14V zener, and a WZ-130 is a 500mW 13V zener.

I have no Zener-eenies doc!

 

[Dingman]

OK, lets try this again- Repair is complete - AGAIN.

The shorting that I did caused D10 on board AWR-030 to fail. Although I replaced several other parts, they all tested "OK" (some caps were way off). It was at D10 that the unit started working again.
Here's the final measurements. (in picture).

Now, I need to re-assemble AGAIN and that's where I shorted the output heatsink to the bottom of 027. Spark! Fudge!

I'll make sure to discharge ALL caps I can touch to make sure this doesn't happen again. It was a good lesson, I'm glad it wasn't a hard repair, this SECOND time due to my negligence.

 

[markthefixer]

I keep a couple of 10 ohm 5 watt resistors with test leads handy.

Rule of little finger: if it's bigger than my little finger, it gets the resistor. 10 ohms is fast, but usually no spark on discharge.

otherwise, I usually keep anything conductive out of there.. just an unconscious habit after all these years - had to think about it to realize it.

 

[Dana65]

J

The sa-8100 manual is a bit less helpful than others - they were learning.

Download this one if you haven't, it's 90 meg and readable.

boards have a zzz-999 designation to identify them, then there are the C1, Q1 etc designations.

Each board is broken out in the second half of the manual, showing schematic with component identification, then a board diagram (from the bottom!) also with component identification.

I will have to teach you about the three transistor leads, and how to use the symbol on the board to correctly install each transistor, avoiding the 5 incorrect possibilities and getting the 6th (and correct) installation.

The symptoms you describe is the classic power amp transistor failing model (most likely the 2sc1451). DON'T run it, it CAN spontaneously turn itself into a smoking ruin that needs many high powered components including output transistors.

Hello mark ,
For some reason l'm having a hard time trying to download that file you suggested for the pioneer SA-8100 amplifier guess it's broken , l did try to download it from hifi logged in but it seems broken too .
Hope you can point me in the right direction. Much appreciated

 

[markthefixer]

I just downloaded them all from hifiengine just now , and opened / examined them.

problem's gotta be on your end....

check your reader, or just reload it.

 

[Dana65]

I just downloaded them all from hifiengine just now , and opened / examined them.

problem's gotta be on your end....

check your reader, or just reload it.

Ok
Thanks for the response