The Pioneer C-4500 is a lovely old turntable/amp unit.
This one is in great condition, but the one channel is distorted.
When I got it, it was heavily distorted. I did some work, and now it is far less, but still a little, distorted.
I need to know what to look at next?
The inside is incredibly simple, with 4 discrete PC boards: PSU, Phono Equaliser, Tone control (pre-amp) and Main Amplifier.
All easy to get to, and work on :thumbs:
I suspected one of the 4 heatsink-mounted D525 transistors, and replaced all 4 with new ones. While I had the main amp board out, I replaced all the capacitors, except 2 little 3.3uF 25V caps I could not find. (They are bipolar NPN transistors, and testing them with the DMM I got 3.2-MOhm on collector and emitter legs of 3 of them, but 3.2-MOhm on the collector and 8-Ohm (not MO) on the emitter of the last one. This made me replace them all?)
After this the sound got much better, but it is not as it should be - some distortion on just the one channel, which gets worse when the "loudness" switch is activated.
I'd like to know what people think I should do next - re-cap the pre-amp (tone-control) board, or replace some of the other little transistors on the Main Amp board?
As is clear, I have little knowledge, so my fixing attempts are little more than sort of logically testing and replacing components, and holding thumbs! I do not have a scope, just a DMM. I am getting pretty good at unsoldering and soldering!
Any advice appreciated, and will be tried.
Regards,
Johan
PS. I do want to fix this myself, so I am not looking for "bring it to me / take it to a proper tech" offers and advice
This one is in great condition, but the one channel is distorted.
When I got it, it was heavily distorted. I did some work, and now it is far less, but still a little, distorted.
I need to know what to look at next?
The inside is incredibly simple, with 4 discrete PC boards: PSU, Phono Equaliser, Tone control (pre-amp) and Main Amplifier.
All easy to get to, and work on :thumbs:
I suspected one of the 4 heatsink-mounted D525 transistors, and replaced all 4 with new ones. While I had the main amp board out, I replaced all the capacitors, except 2 little 3.3uF 25V caps I could not find. (They are bipolar NPN transistors, and testing them with the DMM I got 3.2-MOhm on collector and emitter legs of 3 of them, but 3.2-MOhm on the collector and 8-Ohm (not MO) on the emitter of the last one. This made me replace them all?)
After this the sound got much better, but it is not as it should be - some distortion on just the one channel, which gets worse when the "loudness" switch is activated.
I'd like to know what people think I should do next - re-cap the pre-amp (tone-control) board, or replace some of the other little transistors on the Main Amp board?
As is clear, I have little knowledge, so my fixing attempts are little more than sort of logically testing and replacing components, and holding thumbs! I do not have a scope, just a DMM. I am getting pretty good at unsoldering and soldering!
Any advice appreciated, and will be tried.
Regards,
Johan
PS. I do want to fix this myself, so I am not looking for "bring it to me / take it to a proper tech" offers and advice
