drbacklash
Active Member
This is a continuation of an earlier thread about the 717 not coming out of protection mode but I followed Leestereos instructions on improving the power and driver boards so now I have different problems.
Some background, I got this unit a few years ago and cleaned all the boards, replaced most of the caps, cleaned the pots and replaced the relay. It worked fine and I used it for a while until I stored it for a couple of years. Recently I pulled it out again, turned it on without using the dim bulb for protection (I know, not smart) and it would not come out of protection. I couldn't get the DC offset adjusted so I put it away again until I saw Leestereos post.
I pulled both driver boards and the power board and replaced the aluminum caps, diodes and resistors greater than 1/2 W with metal film resistors. I also replaced the relay. I checked all solder joints and checked the traces for continuity.
The good news is the 717 now comes out of protection mode. The bad news is it probably shouldn't. With my MM test probes on the left channel (F2721 board), he offset starts at 0 mv and increases by one to 400 mv and starts over again. That is with the speaker switch off. If I move it to A (where the probes are), the MM reads a steady 6.04 V. At B it does the recycle from 0 to 400 mv loop thing. At A+B it reads 6.05 V. At all these settings, the protect light is steady on, not flashing and I heard the relay click at the beginning.
Moving to the right channel (F 2722), the same thing happens. I get similar readings throughout the speaker select range. 0 to 400 mv recycle, 6.06 V and 6.06 V. VR 01 and VR 02 are not functional in that moving them does not adjust the readings on either channel. If I ground the negative probe and put the positive one on the test points where you adjust the Bias, then the offset can be adjusted but puts the unit in protect mode. With the unit out of protest mode, the test points show -63.9mv on the right channel and -397mv on the left.
I have a test speaker I use and when I connect it to the 717 and turn it on, it comes out of protect mode. It goes into protect mode when I switch to that speaker (A). Same for L and R. Bias current is adjustable and is on the money.
So, what next? I didn't test or replace any transistors and I'm thinking that is about all that is left to replace. Did I overuse the metal film resistors? I'm willing to keep working on this but I sure hate to have to take that power board out again. I also tested the pins and plugs at the bottom of the driver boards but I didn't know what I should be looking for.
Any suggestions will be appreciated.
Some background, I got this unit a few years ago and cleaned all the boards, replaced most of the caps, cleaned the pots and replaced the relay. It worked fine and I used it for a while until I stored it for a couple of years. Recently I pulled it out again, turned it on without using the dim bulb for protection (I know, not smart) and it would not come out of protection. I couldn't get the DC offset adjusted so I put it away again until I saw Leestereos post.
I pulled both driver boards and the power board and replaced the aluminum caps, diodes and resistors greater than 1/2 W with metal film resistors. I also replaced the relay. I checked all solder joints and checked the traces for continuity.
The good news is the 717 now comes out of protection mode. The bad news is it probably shouldn't. With my MM test probes on the left channel (F2721 board), he offset starts at 0 mv and increases by one to 400 mv and starts over again. That is with the speaker switch off. If I move it to A (where the probes are), the MM reads a steady 6.04 V. At B it does the recycle from 0 to 400 mv loop thing. At A+B it reads 6.05 V. At all these settings, the protect light is steady on, not flashing and I heard the relay click at the beginning.
Moving to the right channel (F 2722), the same thing happens. I get similar readings throughout the speaker select range. 0 to 400 mv recycle, 6.06 V and 6.06 V. VR 01 and VR 02 are not functional in that moving them does not adjust the readings on either channel. If I ground the negative probe and put the positive one on the test points where you adjust the Bias, then the offset can be adjusted but puts the unit in protect mode. With the unit out of protest mode, the test points show -63.9mv on the right channel and -397mv on the left.
I have a test speaker I use and when I connect it to the 717 and turn it on, it comes out of protect mode. It goes into protect mode when I switch to that speaker (A). Same for L and R. Bias current is adjustable and is on the money.
So, what next? I didn't test or replace any transistors and I'm thinking that is about all that is left to replace. Did I overuse the metal film resistors? I'm willing to keep working on this but I sure hate to have to take that power board out again. I also tested the pins and plugs at the bottom of the driver boards but I didn't know what I should be looking for.
Any suggestions will be appreciated.