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SA-8800 protection mode help

alexhastings

alexhastings

Active Member
Hi! I'm trying to get my SA-8800 working - it's stuck in protection mode and I'm at a loss. I've replaced all the components on the GWH-128 board that are marked with a /!\ on the schematic (been meaning to do that amnyways - when this amp was working it had issues with the L channel cutting out), and I've been probing voltages on the AWR-197 board: They all seem ok to me, but have pins 28 and 29 are a little out of spec?

Pin 18: 47.91V
Pin 17: 31.47V
Pin 15: -32.74V
Pin 14: -48.87

Pin 25: 49.14V
Pin 23: -49.24V
Pin 22: -49.26V
Pin 20: 48.79V

Pin 28: -171mV
Pin 29: -167mV

Anyone have any ideas for a next step? Should I think about replacing the /!\ components on the AWR-197 board, or is the relay itself going bad?

Any help is appreciated. thanks!

--Alex
 
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I'm looking at the manual for SA-8800 and there are no GWH-128 and AWR-197 boards. It has GWH-115 and AWR-182 boards. Do you have the right type? If it is the same type only the boards are numbered differently, did you perform the adjustments as per section 9?
 
Pin voltages appear to match the AWR-182, power supply, need confirmation.
Pin 29&29 (~170mV) appears to be dc offset (out of spec) which would point to the main amp board. Have you attempted to
adjust the "DC Balance" as per chapter 9 Adjustment. May need to replace the differential pair with a hfe&Vbe matched pair.
Have you replaced any transistors in the amp? Appears to have some "bad actors", best to wait for a Pioneer specialist
to chime in.
 
Oops, I was looking at the HG variant side of the schematic... (My father miraculously saved the original schematic and manual!) the boards are GWH-124 and AWR-193. This is either the S or the S/G variant - it was bought in Japan, but it could be either, I guess. I'll perform those adjustments and check the voltages tonight and come back - thanks all!
 
Huh. That means that there are (at least?) three variants. Hifiengine only has one. If you could scan your manual and upload that would benefit the community.
 
I can definitely scan my manual and schematic sheet!

Haven't replaced any transistors yet, just resistors and caps on the GWH-124 board. I used the service manual on hifiengine, which has the board layout for the GWH-115. They were almost identical - just one spot where a couple of resistors were out of order...nothing too hard to figure out!

@petehall347 here are those voltages:

D13 anode: -67mV DC

Q2 Voltages
B: +2.6mV DC
C: 49.28V DC
E: -0.46mV DC

Had no luck with the DC offsets - measured about 0.2mV on pins 15 and 20 no matter what I did to VR5-6... Going to make sure I'm getting power to the board now.

New edit. All voltages to power amp board appear to be ok - +-48/50V on every pin that's supposed to have it...
 
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Got the schematic sheet scanned in and submitted to hifiengine. Looks like the manual is the same, but my schematic scan is definitely higher quality than the one in the service manual! If anyone wants it while hifiengine is working on getting it up, I'm happy to throw it on my dropbox - just let me know.
 
Cool! Hifiengine usually takes 1-2 weeks to process. I always upload my scans in 300 dpi B&W/color as readymade PDFs using GIMP and Imagemagick.
 
check q1 q3 q4 for emitter to collector short circuit .
also check d15 . and r7 .
also c24 might have gone short .
 
alexhastings said:
Got the schematic sheet scanned in and submitted to hifiengine. Looks like the manual is the same, but my schematic scan is definitely higher quality than the one in the service manual! If anyone wants it while hifiengine is working on getting it up, I'm happy to throw it on my dropbox - just let me know.
Click to expand...
You can also post it to the Audiokarma database, see here for info: https://audiokarma.org/forums/index.php?threads/please-help-the-ak-database.349095/
 
alexhastings said:
Got the schematic sheet scanned in and submitted to hifiengine. Looks like the manual is the same, but my schematic scan is definitely higher quality than the one in the service manual! If anyone wants it while hifiengine is working on getting it up, I'm happy to throw it on my dropbox - just let me know.
Click to expand...
Hello, I'm working on my SA-8800 also now, looking for vr5 and vr6 (lol). I sure would like a better schematic; mine is okay... from HFE. Thanks
-John
 
Checked for those shorts (the resistances were floating around quite a bit with the unit off, so I ended up turning it on and looking at the voltages between the terminals of each component instead. Didn't find any shorts...

Q1 C (+) to E (-): 0.57V
Q3 C (+) to E (-): 0.63V
Q4 C (+) to E (-): 0.68V
D15 (Anode (+) to cathode (-): -0.34V
R7 (pin 20 side: +) to other side (-): 49.3V
C24 (+) to (-): 0.99V

The resistances (with unit off) agree with with these measurements - I didn't measure any shorts that way either!

John I'll get the schematic scan up on audiokarma tonight. I wish I had the board layout to scan too - the HFE one is a little tough to read sometimes, but it's kind of a miracle we have one at all, so not complaining!
 
am thinking q1 is shorted if you were to pull it out and is indeed shorted the relay should click so long as everything else is good .its that or r7 might be open or a bad solder joint or cracked trace .
if isnt those it would maybe be quicker to pull q1 q2 q3 q4 and test or replace them
 
I pulled Q1 out and indeed, the relay immediately clicks on. When I shut it off, it takes about 12 secs to click off. I don't measure any shorts on Q1 when it's pulled (C-E measured OL), but clearly something is bad with the BJT, no?

I took out R7 and measured as well, and it's dead on 100Kohm so no worries there.

Replacements for Q1 (2SC945A) - mouser 512-KSC945CGBU look appropriate?

For Q2 (2SC1384) - mouser 512-KSC2690AYSTU?

I am fine rerouting the leads if the pinouts are different - just want to make sure I get the right BJTs in there!
 
i noticed q1 base voltage was low .it should be -1v dc . see what voltage is at d13 anode with q1 removed .
 
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alexhastings said:
Replacements for Q1 (2SC945A) - mouser 512-KSC945CGBU look appropriate?
Click to expand...
No, Use KSC2383 for Q1, it has a much higher Ic rating to handle the high current dump from C24, 1A vs 150mA.
With Q1 in place relay should drop almost instantly, as soon as ac from the transformer is removed.
 
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Q1 and D13, and C22 make the AC present/lost detector. The -1v at the base of Q1 is not critical as long as the be junction of Q1 is not forward biased. Measure AC volts (black to chassis) on the cathode of D13, and anode of D5. Test D13. Measure DC volts on the + side of C7 (bit 12000µF, 63v capacitor).
 
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