PJuddery
Well-Known Member
Hi All,
I've got a Sansui 6060 that I'm in the process of restoring. When I bought it, the left channel was a mess. It had almost nothing but distortion/ static, that was independent of the volume control position or the use of any other controls. The right channel was also rather intermittent, but had clean audio when it was working. Initially I did all of the required control cleaning, multiple times and that did resolve scratchiness that I'd observed when working certain controls and greatly improved the right channel intermittent issue, (but didn't completely sort it, so more on that later), it didn't fix the left channel fault.
That turned out to actually be 2 different faults. The first and most obvious was the 2sa726 transistor pairs on the driver board. I replaced those with exact hfe matched KSA992F pairs in both channels and it then seemed to be working perfectly. That is until a few hours into soak testing, when the issue reappeared.
I later tracked that down to be caused by the 2sc1313 pair on the pre-amp/ tone board and so I replaced those on both channels, with KSC1845F exact matched pairs, (I didn't know if they needed matching, but I figured it couldn't hurt to do so, so I did).
** For anyone reading this in the future, attempting to track down a similar issue, I worked out that the 2nd issue was on the pre-amp/ tone board, because the volume control didn't change the state of the distortion/ static, however, pressing the Audio Muting button made it disappear completely, which meant that the issue was in-between the volume control and the Audio Muting button. Both of those are mounted on the pre-amp/ tone board. **
So, after being convinced that I'd found and fixed the left channel faults, I proceeded to start doing a full restore. I had found it a royal pain to try to find a single supplier that had all of the components that I needed and was going to have to place 3 different orders, with 3 lots of shipping costs, so I ended up bought a rebuild kit, which contains the majority of the components that might be problematic. The caps are all Nichicon PW, Nichicon Muse and Wima, so should be good and reliable.
So far I've rebuilt the power supply and the driver board, the latter of which still needs 1 x 50v 47uf capacitor that didn't come with the kit and also didn't come with a replacement for the 2SC1951 constant current transistors, or the 2SD438 and 2SB560 output driver transistors, but I realised that while I was waiting for the kit to arrive, so I ordered some ZTX694B, KSC2383Y and KSA1013 respectively and I'm planning to replace those today, as well as start working on the pre-amp/ tone board rebuild.
However, after running the unit all day yesterday, (because I was procrastinating taking the whole front end apart to get to the pre-amp/ tone board, which is a pain) and also really enjoying listening to music through it, so didn't want to switch it off to work on it), it got to late last night and I suddenly got a few loud pops through the left speaker and not wanting to risk damaging the speaker, I switched off and disconnected everything.
I'm hopeful that completing the restoration/ rebuild, should eliminate the pops from happening again, so this is probably a moot question, however, I'd really like to know what might have caused that. The channel distortion due to the noisy transistors I understand, but as these have been replaced, as well as almost all of the electrolytics in the power and driver boards, I was wondering if anyone could give me any insight into this?
I know that such a potentially rare intermittent fault may be impossible to definitively track down and prove, but I'd really like to at least learn what the potential causes might be, either for future reference or in case the remaining rebuild doesn't stop it from happening again.
By the way, I set the bias to 15mv on each channel, across the output resistors as per the service manual. This then measures as 20 - 22 mv across the speaker terminals with the volume all the way down and no speakers attached. Also F.Y.I, the trim pots have been replaced with new Bourns pots of the correct value.
Thanks in advance for any replies.
Peter
I've got a Sansui 6060 that I'm in the process of restoring. When I bought it, the left channel was a mess. It had almost nothing but distortion/ static, that was independent of the volume control position or the use of any other controls. The right channel was also rather intermittent, but had clean audio when it was working. Initially I did all of the required control cleaning, multiple times and that did resolve scratchiness that I'd observed when working certain controls and greatly improved the right channel intermittent issue, (but didn't completely sort it, so more on that later), it didn't fix the left channel fault.
That turned out to actually be 2 different faults. The first and most obvious was the 2sa726 transistor pairs on the driver board. I replaced those with exact hfe matched KSA992F pairs in both channels and it then seemed to be working perfectly. That is until a few hours into soak testing, when the issue reappeared.
I later tracked that down to be caused by the 2sc1313 pair on the pre-amp/ tone board and so I replaced those on both channels, with KSC1845F exact matched pairs, (I didn't know if they needed matching, but I figured it couldn't hurt to do so, so I did).
** For anyone reading this in the future, attempting to track down a similar issue, I worked out that the 2nd issue was on the pre-amp/ tone board, because the volume control didn't change the state of the distortion/ static, however, pressing the Audio Muting button made it disappear completely, which meant that the issue was in-between the volume control and the Audio Muting button. Both of those are mounted on the pre-amp/ tone board. **
So, after being convinced that I'd found and fixed the left channel faults, I proceeded to start doing a full restore. I had found it a royal pain to try to find a single supplier that had all of the components that I needed and was going to have to place 3 different orders, with 3 lots of shipping costs, so I ended up bought a rebuild kit, which contains the majority of the components that might be problematic. The caps are all Nichicon PW, Nichicon Muse and Wima, so should be good and reliable.
So far I've rebuilt the power supply and the driver board, the latter of which still needs 1 x 50v 47uf capacitor that didn't come with the kit and also didn't come with a replacement for the 2SC1951 constant current transistors, or the 2SD438 and 2SB560 output driver transistors, but I realised that while I was waiting for the kit to arrive, so I ordered some ZTX694B, KSC2383Y and KSA1013 respectively and I'm planning to replace those today, as well as start working on the pre-amp/ tone board rebuild.
However, after running the unit all day yesterday, (because I was procrastinating taking the whole front end apart to get to the pre-amp/ tone board, which is a pain) and also really enjoying listening to music through it, so didn't want to switch it off to work on it), it got to late last night and I suddenly got a few loud pops through the left speaker and not wanting to risk damaging the speaker, I switched off and disconnected everything.
I'm hopeful that completing the restoration/ rebuild, should eliminate the pops from happening again, so this is probably a moot question, however, I'd really like to know what might have caused that. The channel distortion due to the noisy transistors I understand, but as these have been replaced, as well as almost all of the electrolytics in the power and driver boards, I was wondering if anyone could give me any insight into this?
I know that such a potentially rare intermittent fault may be impossible to definitively track down and prove, but I'd really like to at least learn what the potential causes might be, either for future reference or in case the remaining rebuild doesn't stop it from happening again.
By the way, I set the bias to 15mv on each channel, across the output resistors as per the service manual. This then measures as 20 - 22 mv across the speaker terminals with the volume all the way down and no speakers attached. Also F.Y.I, the trim pots have been replaced with new Bourns pots of the correct value.
Thanks in advance for any replies.
Peter
