Pioneer SA-7100 - low volume

[Jomp]

I bought this vintage Pioneer SA-7100 from a drift store, cleaned it up, changed (swapped out) the filter capacitors, de-oxited the other boards, then connected it through my load lamp - the relay clicked and the light bulb dimmed out. I measured the voltage drops on the rails with my multi-meter and I got close to the specified voltage of 30V, measured the voltages on the control board and the power amp board and they were all there close to specs. I got exited and connected the amp without the load lamp to my test speakers and a CD player - I got sound, no hum or hiss noise, but the volume was quite low - I turned the volume to max and I got sound around the 9 o'clock volume in my Sansui AU4900. I checked and rechecked my work on the re-capped, measured the transistors on all the boards and swapped out some of them but the volume remained low...measured the output transistors - they were all ok. I don't know what is going on with this supposedly 25WPC Pioneer, please, please help...

 

[mbz]

Maybe a preamp power supply issue. Does the amp have pre-out/Main-IN connectors at rear?
Will try and track down service manual

 

[mbz]

Determine if it's a PRE or Power amp problem, 2 tests.
0) verify PRE-OUT/MAIN in jumper links are in place. Remove links
1) connect IPHONE/IPOD/another amp to MAIN-IN of 7100, set volume to minimum, check for audio
2) source connected to 7100, PRE-out to main in of seconds amp, speakers connected to second amp, check for audio

 

[Jomp]

Determine if it's a PRE or Power amp problem, 2 tests.
0) verify PRE-OUT/MAIN in jumper links are in place. Remove links
1) connect IPHONE/IPOD/another amp to MAIN-IN of 7100, set volume to minimum, check for audio
2) source connected to 7100, PRE-out to main in of seconds amp, speakers connected to second amp, check for audio

Excellent suggestions - Why didn't I think of these tests ---- stupido.. will report back soon

 

[Jomp]

Thank you mbz, Marantz cd 63se sounds so good and loud on the Pioneer with direct connection to the Main in. Marantz has volume control on the remote. will have to work on the pre amp board... thanks again mbz

 

[mbz]

check for 30VDC at Pin 12 on the power supply. Often a transistor,diode,, goes taking out audio on both channels

 

[Jomp]

check for 30VDC at Pin 12 on the power supply. Often a transistor,diode,, goes taking out audio on both channels
View attachment 1775858

I will do that tomorrow and will report back. I also suspect the two Jfet transistors on the control board ... they are the K30A that I couldn't find appropriate replacement for.. night buddy..

 

[Jomp]

The transistors on the control board were the culprit. They measured ok on board and off board but they were leaking. The amp was amazing that it could produce sound at a lower volume without any distortion but you could actually hear the bunch, the clarity and sound stage were missing. Thank you mbz for giving me the prompt....

 

[ivandezande]

I would replace every transistor in this unit except for the driver and outputs. I wasn't happy with mine until I did.
The 2SC1451's in the amp HAVE to go. KSC3503.

 

[Jomp]

I would replace every transistor in this unit except for the driver and outputs. I wasn't happy with mine until I did.
The 2SC1451's in the amp HAVE to go. KSC3503.

Thank you ivandezande... the 2SC1451's on the power amp board are the two transistors that I have not replaced but the amp sounds great at the moment. I will source some KSC3503s for future proof. I got a few 100wpc amps but I have to say that I prefer the less powerful amps when listening to music at low volume and long session. The Pioneer is one of the perfect candidates for such an occasion - punchy, crispy, good sound stage .. just right for my ears. The other smaller amps that I really like are the Sansui AU-6500 and Sansui G-4700 - they just have some nuance to their sound..