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Pioneer SA-9900 power supply adjustment procedure

quadmatrix82

quadmatrix82

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Hi Pioneer experts, currently refurbing a SA-9900 and noticed there’s no explanation how to adjust the power supply trim pots seems the only adjustments in the manual are for the bias and dc offset

Can anyone share what the adjustment procedure is for the four trim pots?
 
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rcs16 said:
As a clue, usually the big schematic has critical voltages displayed. Other than that I’d have to look at the schematic
Click to expand...
Ok I had a look, I see +/- 48v on awr070 I’m assuming check against pin 8 and 13?
 
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The VR's appear to be more about setting voltages at Q3, Q9, Q1 bases to set the +58V rail(pin 4). The 48V rail is a side branch off the 58V rail.
Suggest monitor both +58(4) and +48(8) when adjusting +ve rails to spot underperforming/short regulator, repeat for -ve rail -58(5) and -48(13)
 
Thanks Mbz will do and report back here’s a photo of both the power supply boards, so is it a matter of also adjustment inf the other trim pots on awr-077 to +\-58v at pin 5 and 3?
 

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quadmatrix82 said:
I have a bright dim using 75 watt globe, pin 5 gets -6v but pin 4 is 0v
Click to expand...
quadmatrix82 said:
I’m yet to replace 2sd313 and 2sb507 I’ll try that and see
Click to expand...
Pin 4 at 0V means either regulator has failed open, but in this case DBT would be dull, ie no short.
Alternatively Pin 4 at 0V meansthere is a near short near pin 4. Take a punt measure resistance from pin 4 to chassis/GND, compare with pin 5 to GND. I assume pin 4 is a wire wrap post. If it's a connector of any sort then unplug from either end and see if pin 4 normalizes.

Doubtful to be a regulator, if they fail short then the voltage will be higher than expected. Fail open then pin 4 is 0V, in both cases DBT will be dull.
 
mbz said:
Pin 4 at 0V means either regulator has failed open, but in this case DBT would be dull, ie no short.
Alternatively Pin 4 at 0V meansthere is a near short near pin 4. Take a punt measure resistance from pin 4 to chassis/GND, compare with pin 5 to GND. I assume pin 4 is a wire wrap post. If it's a connector of any sort then unplug from either end and see if pin 4 normalizes.

Doubtful to be a regulator, if they fail short then the voltage will be higher than expected. Fail open then pin 4 is 0V, in both cases DBT will be dull.
Click to expand...
Thanks mb I replaced q1/2 2sd313 and 2sb507 with ksc2073/ksa940

2sd313 was shot when removed from circuit tested as a capacitor

Reinstalled the new transistors still 0v on pin 4 and the dim remains bright

Pin 4 and 5 are both wire wrapped

Pin 4 measures 3.5k

Pin 5 measures 5.8k
 
mbz said:
Pin 4 at 0V means either regulator has failed open, but in this case DBT would be dull, ie no short.
Alternatively Pin 4 at 0V meansthere is a near short near pin 4. Take a punt measure resistance from pin 4 to chassis/GND, compare with pin 5 to GND. I assume pin 4 is a wire wrap post. If it's a connector of any sort then unplug from either end and see if pin 4 normalizes.

Doubtful to be a regulator, if they fail short then the voltage will be higher than expected. Fail open then pin 4 is 0V, in both cases DBT will be dull.
Click to expand...
Here are the measurements from the power supply AWR 070 (larger board)
4 -6.8v
5 +6.8v
6. Gnd 0
8 +5v
9 +5v
12 -5v
13 -5v
15 -1.3v
16 0v
17 -5.6v
 
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Awr 077 (small board) power supply measurements:
1 gnd 0
2 -6v
3 -6.8v
4 0
5 +6.5v
6 +6v

all measurements in this post and above on a 75 watt dim
 
quadmatrix82 said:
2sd313 was shot
Click to expand...
quadmatrix82 said:
fixed a bad track I get +\-6v now for pin 4 and 5 but dim still bright
Click to expand...
Was the power supply working normal before starting the refurb?
Reads like you have a fault downstream of pin 4 that vapourised a track and took out the voltage regulator. The DBT is probably preventing a repeat performance.

Plz indicate what track failed, assume it's somewhere on tha 58V rail, between pin 4 and Q1 emitter.

58V/3.5k is only 16mA so no dumb short. Possibly silicon failing under load.

Pin 4 feeds AWR-077(5)
AWH-037(13)
AWM-071(12)

I'd take a punt on AWR-077 because of the low 10ohm R1
Only if you can do easily, lift one leg of R1(10) and R3(4k7), dbt power up, bright?
Failing that I would then look at the other paths from pin 4 and lift components to isolate that path.

maybe the pioneer guys have seen this before and better to advise
 
mbz said:
Pin 4 at 0V means either regulator has failed open, but in this case DBT would be dull, ie no short.
Alternatively Pin 4 at 0V meansthere is a near short near pin 4. Take a punt measure resistance from pin 4 to chassis/GND, compare with pin 5 to GND. I assume pin 4 is a wire wrap post. If it's a connector of any sort then unplug from either end and see if pin 4 normalizes.

Doubtful to be a regulator, if they fail short then the voltage will be higher than expected. Fail open then pin 4 is 0V, in both cases DBT will be dull.
Click to expand...
Thanks Mb, I have no idea if it was working bought it with cord cut, internally was original except some repairs to the power amp module.

The track that failed was 470uf c18 the cap pressed against filter cap and broke track all fixed now

All the transistors on the power supply and power amp boards are replaced outputs changed on one side previously fitted with poor subs

With a 100w dim I heard a arch now replaced with 75w dim for cautionary measures

All new transistors on power
Supply, power amp module, control and input boards

Here’s the latest measurements

Awr 037 power amp board pin 13+6.5v
Awm071 protection board pin 12 +6.5v
Awr070 pin 7 blank pin 8 +5v

Other measurements on Awm 071 protection board
1 -2.2v
2 +1.5v fluctuates approx .5v
3 +2v
5 1.5v
6 1.5v
7 +2v
8 2v
9 - 0 volts
10 +6.5v
11 +6.5v
12 +6.5v

Pins 2,3,5,6,7,8 all fluctuate approx .5v either way
 
OK, so no vapourized track, was a nice theory, only a failed regulator and cut power cord so pre-existing fault.
Don't think psu voltage measurements is the way since the psu is taking a hammering from the high current drain so can't mainting voltages and they fall, eg, 58V rail at 6.5V
mbz said:
I'd take a punt on AWR-077 because of the low 10ohm R1
Only if you can do easily, lift one leg of R1(10) and R3(4k7), dbt power up, bright?
Click to expand...
 
mbz said:
OK, so no vapourized track, was a nice theory, only a failed regulator and cut power cord so pre-existing fault.
Don't think psu voltage measurements is the way since the psu is taking a hammering from the high current drain so can't mainting voltages and they fall, eg, 58V rail at 6.5V
Click to expand...
Thanks yeh its the only shorted transistor I found from the ones replaced but there must be other faults found some leaky caps too

I’ll try the resistors you suggested now and report back

In the interim here’s the power amp module voltages AWM071
1 +5.3v
3 -4.5v fluctuates
7-6v
12 +6.4v
16-6.8v
17-6.8v
21 -4.1v fluctuates
23 +4v fluctuates
24 +4v fluctuates
28 -2v fluctuates
35 -4.8v fluctuates
30 2v fluctuates
 
mbz said:
OK, so no vapourized track, was a nice theory, only a failed regulator and cut power cord so pre-existing fault.
Don't think psu voltage measurements is the way since the psu is taking a hammering from the high current drain so can't mainting voltages and they fall, eg, 58V rail at 6.5V
Click to expand...
Ok tried the resistors
r 1 and r 3 lifted one leg - no change on awr-077
 
Can you pull both 1A fuses F2,F3(AWR-070) then dbt power up confirm dbt is dull/off.
Would point to the regulated supply and downstream of that. Reinstall fuses.

On the AWR-077 measure the volt drop across R2(10) should be less than 180mV. Repeat for R1(10).

You should be looking for signs of stressed resistors, eg, AWM-071 R29(2k4), R27(470)… AWH-037 R81,2,3

Thinking the problem is elsewhere like on the AWR-070(psu) or on another rail.
 
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