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Pioneer SA-9900 issues

Do these measurements warrant more investigation in the power supply section? Perhaps a rebuild/recap?

I measured again the following sections of the amp:

  • AWX-083-2/2 (with respect to chassis ground);
  • C4 across mains, just before entering the primary transformer winding, after F1 8A (Main fuse, 8amps, 250VAC, fast blow);
  • Secondary transformer windings going to relay S17 with respect to chasis ground (unregulated power supply?!);
  • Secondary transformer windings going to AWR-070 with respect to chassis ground AND pin #6 on AWR-070 (regulated power supply?!);
  • C1,C2 filter caps, 22,000uf 63V original parts, across the positive/negative leads;
  • Power supply circuit ass'y AWR-070 (with respect to chassis ground);
  • Protection circuit ass'y AWM-071 (with respect to chassis ground);
  • Power supply circuit ass'y AWR-077 (with respect to chassis ground);
It looks like voltages are way off?

Note that these measurements have been taken with a cheap, no-name, off-the-shelf DMM.


AWX-083-2/2:

#5 8 VAC;
#6 86 VAC;
#7 85,7 VAC;
#8 13,05 VAC;

C4 across mains (snubber): 109 VAC;

Secondary transformer windings going to relay S17:

Orange: 40,84 VAC;
Orange: 40.36 VAC;
White: GND;
Red: 31.95 VAC;
Red: 32,01 VAC;

Secondary transformer windings going to AWR-070:

Green: 53.81 VAC;
Green: 54,22 VAC;
Brown: GND;

Secondary transformer windings used by PL1, PL2, PL3: Measures approx. 7.6VAC <=> 8VAC;

C1,C2 filter caps, 22,000uf 63V original parts, across the positive/negative leads:

C1: +54.85 VDC;
C2: -54.2 VDC;

AWR-070:

#1 53.83 VAC;
#2 54.25 VAC;
#3 GND;
#4 +63.3 VDC;
#5 -63.0 VDC;
#6 GND;
#7 Unpopulated / no wire wrap post;
#8 +53.47 VDC;
#9 +53.49 VDC;
#10 Unpopulated / no wire wrap post;
#11 Unpopulated / no wire wrap post;
#12 -53.90 VDC;
#13 -53.92 VDC;
#14 Unpopulated / no wire wrap post;
#15 -12.95 VDC;
#16 0.00VDC;
#17 19.95 VDC;

AWM-071:

#1 -12.76 VDC;
#2 0.00 VDC;
#3 0.001 VDC;
#4 GND;
#5 0.026 VDC;
#6 0.025 VDC;
#7 0.034 VDC;
#8 0.030 VDC;
#9 0.000 VDC;
#10 9.12 VDC;
#11 63.6 VDC;
#12 63.6 VDC;


AWR-077:

#1 GND;
#2 -49.16 VDC;
#3 -62.3 VDC;
#4 GND;
#5 +63.0 VDC;
#6 +49.66 VDC;
 
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Circling back on my SA-9900 restoration project - I finished both AWR-070 and AWR-077: Power supply boards. I'm using LesE's parts list.

First AWR-070:

The original PCB had no signs of damage besides the heat coloration. Voltages were up to spec. Trimmers VR1 and VR2 33kOhm were very sensitive to adjustments and have been replaced with Bourns 25kOhm multi turn parts.

The original rectifiers 1S1886 / SIB01-02 have been replaced with 1N4004. The ceramic disc capacitors paralleling the rectifiers have been replaced with 10nF Vishay caps X1 Y2 rated.

The original electrolytics have been replaced with Nichicon UHE/UPW series.

The board has been re-transistored as well as per LesE's parts list.

Q1 and Q2: I cleaned the original heatsinks and applied an extremely thin layer of thermal paste. No micas, the originals did not have micas either. I'm looking for additional aluminum heatsinks to be mounted behind the fuses. There's plenty of space.

Important Note: As per LesE's parts list, AWR-070 Transistor Q6, 2SA684A replaced with KSA1220AYS: The KSA1220AYS is discontinued / unavailable. I used Toshiba TTA004B - I confirm this works as expected.

The two zeners, D5 & D6 have been replaced with 1N5243Bs.

D7 - 1S2473 switching diode for the 8V AC rail powering the bulbs (2 x scale, 1 x power light) has been replaced with 1N4148TR. Works well, I have 7.8Vac.

Powered on the DBT, no issues. Powered on mains voltage: voltages are perfect / identical to the manual after slight adjustments on VR1 + VR2. The Bourns trimmers are amazing.

View media item 27859View media item 27860
 
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Next up, AWR-077. Visually the board is OK. I damaged Q3 + Q1 and D1 13V Zener while adjusting VR1 a while ago. My test lead shorted something and Q3's capsule exploded in my face! D1 was damaged, measured something like 2.535V both ways.

D1 + D2 = 1N5243B.
Q1 + Q3 = KSC2383YTA
Q2 + Q4 = KSA1013YBU
C1 + C2 = 10nF / 50V Vishay
C3 + C4 = 47uF / 50V Nichicon UPW
VR1 + VR2 = 10kOhm Bourns trimmers

View media item 27861View media item 27862View media item 27864View media item 27863
 
I'm working on the input circuit assembly board, AWK-038-(C).

For positions Q9,Q10,Q11 and Q12, the PCB holes are too tight for KSA1381 and KSC3503 leads. The underlying copper traces are fragile due to heat damage that occured in the past.

Any suggestions on how to increase the PCB hole diameter without damaging the underlying copper traces?

I had no idea that this board is so sensitive to heat damage, either while in use or while soldering. Special attention should be paid to this assembly while doing soldering work!
 
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This can be done by manually turning an appropriate drill bit in a pin vise- you should be able to widen the holes to accept the larger transistor leads.

grgmchl said:
I'm working on the input circuit assembly board, AWK-038-(C).

For positions Q9,Q10,Q11 and Q12, the PCB holes are too tight for KSA1381 and KSC3503 leads. The underlying copper traces are fragile due to heat damage that occured in the past.

Any suggestions on how to increase the PCB hole diameter without damaging the underlying copper traces?

I had no idea that this board is so sensitive to heat damage, either while in use or while soldering. Special attention should be paid to this assembly while doing soldering work!
Click to expand...
 
try a heated wire first. The flux residue in the hole narrows it, and the heated wire if kept away from the pad will clear it or soften it enough for an insertion. btdt....
less risky than even a hand held drill bit. (1/32 = 0.03125)
 
I used a hot sewing needle after cleaning the pads with soldering wick and using a solder pump. Works well so far - again, this board is very sensitive to heat. I find 375 celsius works best.

a thin drill bit will damage these fragile solder pads
 
grgmchl said:
I used a hot sewing needle after cleaning the pads with soldering wick and using a solder pump. Works well so far - again, this board is very sensitive to heat. I find 375 celsius works best.

a thin drill bit will damage these fragile solder pads
Click to expand...
yes, fragile pads and a drill bit make me shudder and set my teeth on edge - just like fingernails on a blackboard.
 
be careful with the "delicate" wire wrap connections on most of the boards. aged wire plus mechanical disruption equals metal fatigue which can cause electrical issues, there might be voltage but reduced current flow can be difficult to find. if the wire breaks its easier to find, visually speaking. i am working on an sa-9900 now, finished an apt holman amp-1 and waiting on mod parts for a sansui au-717.

variac trio.jpg
dim bulb is just the beginning of a useful trio when doing electrical/electronic diagnostics. kaboom avoidance detection system. a slip with the dmm probe lights up the bulb(s) and not the component in the circuit.
 
I full agree, one should use a DBT when applying power from the mains. A steady hand is always good when probing around.

Good luck with your project.
 
Back on my SA-9900 restoration project.

+-48Vdc & +-58Vdc rails are OK.

I'm testing AWR-070 pin #17 - I'm getting -48Vdc for 3-4 seconds then it goes to 18.3Vdc.

One important detail: All outputs on AWR-070 are disconnected.
The only connections are pins:

#1, #2 - Green secondary wires;
#3, #6 - Connected to chassis ground AND brown center tap on the transformer;

About pin #17 and the +10Vdc, does the amp need to be under load to obtain this voltage?

Based on my previous voltage measurements year 2022 (further up the the thread, I was measuring the same voltage on pin #17, 19.95Vdc).
Thanks!
 
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