Pioneer SA-7500 Repair Help

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Ramen3

New Member
Hey, I'm very new here and honestly very new to working with electronics and vintage amps, although I have enjoyed using them for some time now.

Some time ago, I purchased a Pioneer SA-7500 but have barely used it because there is a growingly noticeable noise after a few minutes of listening, which will remain when selecting an unused input. The volume of the noise stays the same regardless of what volume I set the amplifier at.

I figured the problem most likely comes from bad transistors in the power amplifier assembly (there is no noise when I use the "PRE Out"-output and connect that to a different amplifier) but thought I might as well replace some of the electrolytic capacitors inside as well.

Now I had a look inside and wanted to make a list of parts which I would order replacements for, but when I tried to compare the parts with the schematics in the service manual, a lot of things seemed off and I'm pretty sure someone worked on this amplifier before.

The pictures below show the power amplifier assembly, and I'm mainly focusing on the left channel there, but it's the same on the right channel. Already starting at C1, there's a .47µF 25V instead of 1µF 50V capacitor running in a different orientation than shown on the diagram and another ceramic (??) capacitor (474K, 100V, I'm assuming that's also 0.47µF +/-10%) between C1 and R1 which is not shown at all?

This might have just been me misinterpreting the diagram, but another thing I noticed was the blue electrolytic capacitor in my picture, which is labeled with 6.3V 2200µF, seems to be C7 on the diagram, which should only have a capacitance of 220µF according to the parts list and the diagram. What am I missing here? Is the schematic in the service manual simply of a different type of SA-7500, am I misinterpreting the information, or are there actually incorrect parts installed here?

Any help would be greatly appreciated!

Screenshot 2023-02-19 021425.png
The image above is a diagram/schematic of the power amplifier assembly.

Screenshot 2023-02-19 031722.png
Parts list of the power amplifier assembly

IMG_2873 - Copy.jpg
Top-Down-View of the power amplifier assembly

IMG_2876 - Copy.jpg
View around the left channel in on pin 7, numbers are harder to make out than I hoped.
 
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Not that you can't get good help in this forum but I would highly suggest posting this in the Pioneer forum.
 
mea2112 said:
The rules say no duplicate threads for each topic so it would be best to copy/paste this into the Pioneer forum and delete this thread.
Click to expand...

Unfortunately, it looks like I can't delete the thread on my own, unless I'm looking in the wrong place.
 
In that case I wouldn't worry about it. If a moderator sees that you duplicated this thread in the Pioneer forum they'll just delete this one.
 
Ramen3 said:
Hey, I'm very new here and honestly very new to working with electronics and vintage amps, although I have enjoyed using them for some time now.

Some time ago, I purchased a Pioneer SA-7500 but have barely used it because there is a growingly noticeable noise after a few minutes of listening, which will remain when selecting an unused input. The volume of the noise stays the same regardless of what volume I set the amplifier at.

I figured the problem most likely comes from bad transistors in the power amplifier assembly (there is no noise when I use the "PRE Out"-output and connect that to a different amplifier) but thought I might as well replace some of the electrolytic capacitors inside as well.

Now I had a look inside and wanted to make a list of parts which I would order replacements for, but when I tried to compare the parts with the schematics in the service manual, a lot of things seemed off and I'm pretty sure someone worked on this amplifier before.

The pictures below show the power amplifier assembly, and I'm mainly focusing on the left channel there, but it's the same on the right channel. Already starting at C1, there's a .47µF 25V instead of 1µF 50V capacitor running in a different orientation than shown on the diagram and another ceramic (??) capacitor (474K, 100V, I'm assuming that's also 0.47µF +/-10%) between C1 and R1 which is not shown at all?

This might have just been me misinterpreting the diagram, but another thing I noticed was the blue electrolytic capacitor in my picture, which is labeled with 6.3V 2200µF, seems to be C7 on the diagram, which should only have a capacitance of 220µF according to the parts list and the diagram. What am I missing here? Is the schematic in the service manual simply of a different type of SA-7500, am I misinterpreting the information, or are there actually incorrect parts installed here?

Any help would be greatly appreciated!
Click to expand...

1. Looks like someone has been replacing parts. Those caps don't look original. Replace C1 with 1uf UKL or Kemet R82 or Wima MKS2
2. C7 should be 220uf/6.3v - replace with UES 220uf 16v (you can use UKT,FM,FC,FR)
3. The popping noise is most likely from 2SA726. Replace with KSA992FBU
4. 2SC1451 is problamatic as well - replace with KSC3503DSTU

Be careful the pin outs of replacement transistors can be different. Use the silk screen on the board to orient replacements correctly.

5. Before replacing any other parts - test your work from 1 through 4 while the amp is on a dim bulb.
6. A full restoration after the repair is recommended

Hope this helps
 
Last edited:
p4spooky said:
1. Looks like someone has been replacing parts. Those caps don't look original. Replace C1 with 1uf UKL or Kemet R82 or Wima MKS2
2. C7 should be 220uf/6.3v - replace with UES 220uf 16v
3. The popping noise is most likely from 2SA726. Replace with KSA992FBU
4. 2SC1451 is problamatic as well - replace with KSC3503DSTU

Be careful the pin outs of replacement transistors can be different. Use the silk screen on the board to orient replacements correctly.

5. Before replacing any other parts - test your work from 1 through 4 while the amp is on a dim bulb.
6. A full restoration after the repair is recommended

Hope this helps
Click to expand...

Ah, so I guess I was correct when concluding that the caps someone used to replace the originals have incorrect values. I'll replace the parts according to the parts list in the service manual then. I'll certainly go step by step with a dim bulb. Thanks for your help!
 
p4spooky said:
1. Looks like someone has been replacing parts. Those caps don't look original. Replace C1 with 1uf UKL or Kemet R82 or Wima MKS2
2. C7 should be 220uf/6.3v - replace with UES 220uf 16v (you can use UKT,FM,FC,FR)
3. The popping noise is most likely from 2SA726. Replace with KSA992FBU
4. 2SC1451 is problamatic as well - replace with KSC3503DSTU

Be careful the pin outs of replacement transistors can be different. Use the silk screen on the board to orient replacements correctly.

5. Before replacing any other parts - test your work from 1 through 4 while the amp is on a dim bulb.
6. A full restoration after the repair is recommended

Hope this helps
Click to expand...
This thread is a little old now but I will toss in my two cents. The capacitors referenced are indeed the correct values (.47uF/25v) The manual was printed prior to Pioneer changing the valued that are stated in the service manual. I have restored several of these amplifiers and each one came with those little blue capacitors on that board and on the AWH 018 or the AWH 015 board. Both are the same boards just some have a different number printed on it verse what the service manual lists. I would disregard the service manual and replace with the same value of capacitor that was pulled from the board.
 
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