Pioneer SA-9800 rebuild

AFJ

New Member
Over the last week I rebuilt my recently acquired SA-9800. The reason for the rebuild was to ensure reliability.

The following were the power supply voltages before the rebuild. Values in bold are from my amplifier


AWR-194 (Power Supply Assy)



pins 1&2: -51.9v regulated, -52v
pins 3&4: +52.5v regulated, +52v
pins 5&6: +32.4v regulated, +32v
pin 7: +19.2v regulated, +18v
pin 8: 0v, ground
pin 9: -53.1 -50v, raw, unregulated
pins 10&11: -32.6/ 32.6 v regulated, -32v
pin 12: 50.7 +49v unregulated raw
pin 13: 70.4 +69v unregulated raw
pin 14: 0v, ground
pin 15: -71.5 -70v unregulated raw
pin 16: 54.3 +6.7vac, this is an AC voltage - this voltage was taken while the pilot light was burnt.
pin 17: 54.4 +53.4vac, this is an AC voltage
pin 18: 54.6 +53.7vac, this is an AC voltage

This is the pic before the repair -
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As you can see it is in pretty good nick

This is a pick after the rebuild.
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Please note that I have soldered the D4 diode in the wrong direction, I corrected this after the picture was taken

What I have done is -

Change upgrade all transistors apart from Q5 and Q6 as per Solutionrooms list.
Change all diodes
Change all resistors to high precision military grade metal films of the same power rating except the R20 because I could not find a similar heat handling metal film.
The board has been upgraded to the AWR-196 European/HG version with 4 transistors to handle the heat with new heat sinks. The new heat sinks are 26mm tall and touches the metal undercover when closed. So these heat sinks have been isolated from the collector of the transistor with silicone pads sandwiched between thermal paste.
I left the ceramic caps alone.

I did not change the chassis mount R1 and R2 between pins 15&9 and pins 12&13

These are the voltages after the rebuild.

pins 1&2: -50.9v regulated, -52v
pins 3&4: +50.9v regulated, +52v
pins 5&6: +31.5v regulated, +32v
pin 7: +18.5v regulated, +18v
pin 8: 0v, ground
pin 9: -55.1 -50v, raw, unregulated
pins 10&11: -31.3 v regulated, -32v
pin 12: 51.9 +49v unregulated raw
pin 13: 72.3v +69v unregulated raw
pin 14: 0v, ground
pin 15: -71.5 -70v unregulated raw
pin 16: 55.3 +6.7vac, this is an AC voltage - this was before the pilot lamp was replaced.
pin 17: 55.3 +53.4vac, this is an AC voltage
pin 18: 55.3 +53.7vac, this is an AC voltage

My findings

The Q11,12,13 and 14 still run finger burning hot. I'm not sure whether I converted 2 burning transistors to 4 burning transistors.

My questions

1) Will replacing the chassis mount R1 & R2 will help to bring the pin 9 and 12 voltages more towards the spec?

2) I have a few 2SK30A-Y transistors, will replacing the Q5 & Q6 with these will be a good idea?
 
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The protection circuit.

This is a pick before the rebuild.

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This is the picture after the rebuild.

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Accessing the board is pretty difficult and chassis has to be dismantled to do it.
This had some pioneer factory modifications (details of this can be found in AK)

What I have done

Replace all the transistors
Replace all the caps
Replace all the diodes apart from one ( this had a PCB footing come off probably during a pioneer modification, so I left it alone)
I replaced all the resistors apart from the big metal oxide resistors because of heat handling capability.
Finally I replaced the relay.
 
Rectifier board

I replaced the filter caps (18000 uf, 80V), all diodes and the film caps.
The big metal oxide resistor was left lone.

This is a picture of the board after I removed the filter caps.

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Unfortunately I did not take a picture after the replacements.

Observations

When I powered the amp with a 100W DBT it filed to go completely dim or trigger the relay. So I had to plug it in to the main power directly to charge the caps and get the relay triggered.
 
The main amp boards

Not much work was done here.

All trim pots were replaced.
C1,2 C11,12 C13,14 were replaced but, I replaced C1&2 with WIMA poly films.
As suggested by Markthefixer to me I replaced Q7,8,9,10,11,12,21 and 22.
The zener diodes were replaced as well
Finally replaced the driver transistor heat sink grease.

Unfortunately no pictures to show.
 
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EQ board

All caps were replaced as suggested in Solutionrooms thread except that C3 to C6 were replaced with ELNA caps.
I chose to replace C1 & C2 with WIMA poly film caps
As suggested by Markthefixer Q9,10,23,24,25,26,27,28 were replaced.

I think I should have replaced all the trim pots as well

Accessing the board involved fair bit of chassis disconnection

This is a after rebuild picture.
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TC board

I replaced all the electrolytic caps
Replaced Q5 & Q6
I replaced Q3 and Q4 with two of KSA992FBU's. This was recommended to be done because the original five legged transistors were accused of being "noisy" on this site.

This is the picture after the repair.

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Finally the Indicator board

This is a picture after all electrolytic caps were replaced

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I replaced C3 and C4 with WIMA film caps for reliability
 
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After all the upgrades the amp sounds better and I hope that it lasts for a long time.
After much consideration I chose to replace the pilot lamp with an incandescent bulb rather than an LED (which looks much whiter)

I still have to replace the heat sink grease under the power transistors.

I am a novice to electronics and vintage amps. My electronic knowledge is high school, this is my second ever recap/rebuild.

The point of this post is that with a lot of preparation, reading, patience and rechecking your work again and again, anyone should be able to take on a complex amp like the SA-9800. But the process is exhausting and took me 3 full days of working very long hours.

Please don't forget to reply to my power supply board questions.
 
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My findings

The Q11,12,13 and 14 still run finger burning hot. I'm not sure whether I converted 2 burning transistors to 4 burning transistors.

My questions

1) Will replacing the chassis mount R1 & R2 will help to bring the pin 9 and 12 voltages more towards the spec?

2) I have a few 2SK30A-Y transistors, will replacing the Q5 & Q6 with these will be a good idea?

q11 and q12 I can see, but q13 and q14 on a power supply board??? Perhaps you meant q1 and q2, the four power pass elements?

re: heat - if there is room, add heat sinks, and allow for airflow for cooling

re: r1, r2 and voltages. NO. They are FINE.

re: q5 and q6, they are working fine - save the 2sk30a-y for something important in the future.
numbers on lists don't necessarily indicate preemptive replacement, but are provided for repair sourcing when they are zapped.
almost ALL jfets in these lists are in the "leave them be" category. Changes will be specifically called out.
 
Hi Mark, thank you for the input

q11 and q12 I can see, but q13 and q14 on a power supply board???

In the AWG-196 power supply board (HG model) the 2 extra MEJ transistors are called Q13 and Q14. They are similar to Q11 and Q12.

AWR-196 q13 2SD712 863-MJE15030G pnp to-220
AWR-196 q14 2SB682 863-MJE15031G pnp to-220

You can see them besides the 2 usual MJE's with the heat sinks in the picture - see the difference between the before and after pictures.

There are 4 extra resisters as well. They are called R24 to R27 - 4.7 Ohm 1/4W (you can see them in blue between the 2 rows of MJE's)

re: heat - if there is room, add heat sinks, and allow for airflow for cooling

With regards to the new heat sinks, on the additional MJE's - though they are aluminium they are bigger and finned so I think they conduct the heat better than the originals in the other 2 MJE's - but still all 4 run very hot.

I am happy to leave the Q5 & Q6 and R1 and R2 alone.
 
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