Hello,
I just registered to explore some opinions. I've been on this project for a few months now and have made some progress. My apologies that this may get a bit long.... Sansui 881 - Owned since new / Owned since new and played well until October 2020 / Protect relay stopped closing / then the fun started. I probably should have measured the DC offset right away but wasn't educated enough then, to do that.
I found a darkened area on the Power Supply board around one of the TO-220 type transistors and associated Caps. So my take was that the system was 45 years old and needed new everything. I've only addressed the power supply board and have replaced most of the caps with newer type aluminum polymer, then the two TO-220 type transistors and the three TO-92 transistors with replacements recommended from Digi-Key. Nothing improved, so I decided to immerse myself in the operation of the board and started taking voltage measurements at every test point defined in the service manual and at other component connections trying to assess why the amp wasn't getting power out. I'm using a DBT at 100 watts, it goes out when the system is powered up / The entire board as been gone over quite a few times, measuring components in circuit and a few other components were swapped out for newer, ie; metal film resistors plus anything that didn't pass muster on measurement. Some resistors were replaced when they didn't pass on the tests, only to find they were good off the board . However, there are correct plus and minus voltages at many of the correct points, but the driver board is not getting pass thru on all the slot points. ( if anyone is familiar with a Sansui)
Today I went back and checked the old TO-92 transistors and found them good, so I put them back on the board and went about checking voltages again. To my surprise, as I proceeded down one rail, I placed the probe on a point and heard a click from the Relay. This would recur at more than a half dozen places on the board.
This has never happened before, so I thought now was a good time to check the DC offset and found pretty high readings on all three speaker set ports. These were something like 34.5Mv R and 13.5Mv L or similar on all three. Given the info I have now, that's definitely a reason for the relay to stay in protect, but the values are a quite a bit higher than I would have even anticipated. What I expected was more like 0.05 - 1.00 mv difference. Would the variable resistors will even address a difference this high? Is there anyone that can guide me thru the fine points of adjusting this and is this a reasonable approach?
thanks for your time
I just registered to explore some opinions. I've been on this project for a few months now and have made some progress. My apologies that this may get a bit long.... Sansui 881 - Owned since new / Owned since new and played well until October 2020 / Protect relay stopped closing / then the fun started. I probably should have measured the DC offset right away but wasn't educated enough then, to do that.
I found a darkened area on the Power Supply board around one of the TO-220 type transistors and associated Caps. So my take was that the system was 45 years old and needed new everything. I've only addressed the power supply board and have replaced most of the caps with newer type aluminum polymer, then the two TO-220 type transistors and the three TO-92 transistors with replacements recommended from Digi-Key. Nothing improved, so I decided to immerse myself in the operation of the board and started taking voltage measurements at every test point defined in the service manual and at other component connections trying to assess why the amp wasn't getting power out. I'm using a DBT at 100 watts, it goes out when the system is powered up / The entire board as been gone over quite a few times, measuring components in circuit and a few other components were swapped out for newer, ie; metal film resistors plus anything that didn't pass muster on measurement. Some resistors were replaced when they didn't pass on the tests, only to find they were good off the board . However, there are correct plus and minus voltages at many of the correct points, but the driver board is not getting pass thru on all the slot points. ( if anyone is familiar with a Sansui)
Today I went back and checked the old TO-92 transistors and found them good, so I put them back on the board and went about checking voltages again. To my surprise, as I proceeded down one rail, I placed the probe on a point and heard a click from the Relay. This would recur at more than a half dozen places on the board.
This has never happened before, so I thought now was a good time to check the DC offset and found pretty high readings on all three speaker set ports. These were something like 34.5Mv R and 13.5Mv L or similar on all three. Given the info I have now, that's definitely a reason for the relay to stay in protect, but the values are a quite a bit higher than I would have even anticipated. What I expected was more like 0.05 - 1.00 mv difference. Would the variable resistors will even address a difference this high? Is there anyone that can guide me thru the fine points of adjusting this and is this a reasonable approach?
thanks for your time