Go Back   Home > Forums > >
Home Forums Rules Articles diyAudio Store Blogs Gallery Wiki Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

Solid State Talk all about solid state amplification.

Help! Repairing a Pioneer SA-8100
Help! Repairing a Pioneer SA-8100
Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Thread Tools Search this Thread
Old 6th February 2013, 09:05 AM   #11
madtecchy is offline madtecchy  England
diyAudio Member
Join Date: Dec 2010
Location: wigan
My eyes are not t0o good today im having a little difficulty reading the schem.. from what you say i believe R31 acted as a fuse . If the output devices are ok i would first be looking for a faulty semi not too much of a pita as only a few to check. You say pin 14 has 30 or so volts . Just to check is the pin 14 you mention on the left of the pwr amp scem.. If so im sure it should be conected to ground ??

Last edited by madtecchy; 6th February 2013 at 09:10 AM.
  Reply With Quote
Old 6th February 2013, 09:08 AM   #12
mjona is offline mjona  New Zealand
diyAudio Member
Join Date: Jul 2007
Location: Upper Hutt
The protection circuit contains a single four pole relay which stops switch on and switch off noises getting through to both speakers.

It also prevents excessive d.c. getting to your speakers where the heat would pose a serious fire risk to the extend of losing your speakers and even having a house fire. A d.c. fault in either channel will prevent the relay from activating which is almost certainly the reason you are getting no sound on headphones.

As Mooly has pointed out, also alluded to by me, you need to quantify the d.c. voltage at the output of the faulty channel.

R31 has burnt out because too much current has been drawn through it and this raises the question of damage to transistor junctions through which this might have passed. There are two transistor whose collectors connect to R31 and these drive an NPN power device whose PNP counterpart was replaced at some time in history because of some fault and the NPN device may now be suspect.

You have replaced R31 but that has not cleared the fault so you need to know what level of current is passing through that now. Similarly you need to know what level of current is passing through the emitter resistors for the power devices.

You should be able to spot any problems by measuring the voltages across all these resistors, and comparing them with the circuit equivalents in the other channel.

If you would note these respective measurements and report your results it will help with further suggestions on solving your problem.
  Reply With Quote
Old 6th February 2013, 09:31 AM   #13
madtecchy is offline madtecchy  England
diyAudio Member
Join Date: Dec 2010
Location: wigan
IMHO i believe the main cause of this fault can be found with the power off. All them voltage measurments on both boards pose a big risk at this stage it would be easy to end up with two dead channels as for the other channel it is only assumed to be working so can not realy be trusted as a good ref point..
  Reply With Quote
Old 6th February 2013, 01:16 PM   #14
sonata149 is offline sonata149  Malta
diyAudio Member
Join Date: Sep 2006
Location: Malta, Europe
Thank you all for your time and advice. Problem is I'm on and off on this job.
Seems I still have problems with my power amp section.

I've powered it through the series lamp to measure voltage at "pin3". It was -3.5V (quite off) while on "pin23" it was -0.12V. I also measured the voltage between the 2 complimentary pairs at "pin E" where it should be -38V. There the reading is 0V!! At the collectors (pins 36 & 27) the voltage is 37V which is very close.

You made me realise that pin 3 and 23 are the input to the protection circuit so it's beginning to make sense, at least logically if not technically. Now, how do I get pins 3 and 23 to 0V? VR3 and VR4 perhaps?

Thanks again for your help.
  Reply With Quote
Old 6th February 2013, 05:57 PM   #15
Mooly is offline Mooly  United Kingdom
diyAudio Moderator
Mooly's Avatar
Join Date: Sep 2007
Help! Repairing a Pioneer SA-8100
Your fault is almost certainly related to the driver transistors, possibly the outputs and related circuitry.

With the amp OFF you need to confirm that the following are OK.

D5 and D7 and the pot could be suspects as to the initial fault. You can apply a short (the blue line) using a piece of wire. The amp is safe to power up with this applied and will work correctly. This forces the output stage to zero bias current. The amp will still work and all the voltages can still be checked with it like this.
Attached Images
File Type: jpg Capture.JPG (119.9 KB, 24 views)
  Reply With Quote
Old 6th February 2013, 08:51 PM   #16
mjona is offline mjona  New Zealand
diyAudio Member
Join Date: Jul 2007
Location: Upper Hutt
Pin E is an earthing point and there should be no connection with the power rails. There are decoupling capacitors for the power transistors between collector and earth. These are there for stability reasons.

You appear to have measured the positive rail on one channel for voltage with the negative rail on the other. 37 volts is not necessarily out of spec as some variation in mains could account for that. All four devices should register that +/- values at that level.

You will not be able to eliminate the -3.5 volt d.c. by adjustments to a trim pot. You can do that when you have eliminated the fault. You can then do both channels together. Minus 0.12 volts d.c. is somewhat out of spec but it will not cause any harm to your speakers.

In my experience in repairing d.c. faults the most likely cause is a problem transistor.

In addition to measuring the resistors and diodes in circuit with the power off you can check the diode junctions of the three transistors mentioned by Mooly under the same conditions.

In each of these there should be a forward diode junction between collector and base and between base and emitter. The junctions should conduct only in the forward direction. You will be able to use the diode check function on your meter for that.

You have three transistors in series and any may affect another in circuit and you may get some strange results especially if there is a fault. However if the other channel is working correctly which I think is the case the equivalent readings will be valid and you can cross reference the results to account for any disparities you find.
  Reply With Quote


Help! Repairing a Pioneer SA-8100Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
Pioneer sa-610 wiseboy1900 Solid State 1 14th September 2011 05:40 PM
Pioneer SA-1050 PR116 Solid State 0 3rd November 2009 05:59 PM
Pioneer SA 9500II Big_Bill Solid State 15 14th September 2009 02:15 AM
FS: Pioneer TX-8100 Tuner pjanda1 Swap Meet 1 5th October 2005 01:03 AM
Pioneer SA-8800 Lorne Solid State 13 21st June 2004 09:56 PM

New To Site? Need Help?

All times are GMT. The time now is 07:38 AM.

Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 15.00%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.
Copyright ©1999-2017 diyAudio