PL400 II Resurrection
- Thread starter TapeHeadOne
- Start date
'Were it not'. Autocorrect snafu, gimme a break, it was 5.30 am when I posted it, and I was already heading out the door. And my phone's native tongue is Flemish.
After checking some dodgy wiring on the power transistor side of things yesterday night the bios voltage went up do around 0.05V. Let's say I have an 'adjustment range' now between 0.04 and 0.075V.
I wouldn't read to much into the difference between the bias transistor C-E and Q6/Q9, because the bias transistor measurement was a bit of and afterthought and not taken at the same time. Will do if required.
Incidentally, R21 and R30 are fine, even that botch repair I made on 30 is doing OK.
I'm trying to get a handle on how the left OK channel dropped by a factor 10 when I fixed the right one. How did I create a voltage devider (yeah making a sink, but where ?). I didn't touch left ! I think it happened at the same time that base wire worked itself loose.
I don't understand the sexy nurse babe thing but it sounds interesting ! AFTER I get this amp fixed
Peter
After checking some dodgy wiring on the power transistor side of things yesterday night the bios voltage went up do around 0.05V. Let's say I have an 'adjustment range' now between 0.04 and 0.075V.
I wouldn't read to much into the difference between the bias transistor C-E and Q6/Q9, because the bias transistor measurement was a bit of and afterthought and not taken at the same time. Will do if required.
Incidentally, R21 and R30 are fine, even that botch repair I made on 30 is doing OK.
I'm trying to get a handle on how the left OK channel dropped by a factor 10 when I fixed the right one. How did I create a voltage devider (yeah making a sink, but where ?). I didn't touch left ! I think it happened at the same time that base wire worked itself loose.
I don't understand the sexy nurse babe thing but it sounds interesting ! AFTER I get this amp fixed
Peter
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This thing needs to get of my workbench this weekend, or it gets buried.
Now, when the R channel base wire came off, r channel bias on the Test point went to 20V, and the left, previously at .375 as it should be, collapsed.
Reconnecting the base wire dit not bring the bias back up on the L chan, but did drop the R chan bias to the same order as the now collapsed L channel.
Since I'm measuring on what is essentially the base return (why is it called the 'bootstrap' ?) can anyone please tell me what the value on pin 9 is supposed to be ?
Additionally would it be useful to disconnect pin 5 on the display in case there's a short there ?
Edit : disconnecting the meters did not change matters. The low output on BOTH pin 9's I find suspicious. There's only around 0.9V there.
Now, when the R channel base wire came off, r channel bias on the Test point went to 20V, and the left, previously at .375 as it should be, collapsed.
Reconnecting the base wire dit not bring the bias back up on the L chan, but did drop the R chan bias to the same order as the now collapsed L channel.
Since I'm measuring on what is essentially the base return (why is it called the 'bootstrap' ?) can anyone please tell me what the value on pin 9 is supposed to be ?
Additionally would it be useful to disconnect pin 5 on the display in case there's a short there ?
Edit : disconnecting the meters did not change matters. The low output on BOTH pin 9's I find suspicious. There's only around 0.9V there.
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No (and there's only 2A in there), but it ate the 2 MPS 651s. Yes. BOTH channels. Everything else seems to have survived. Didn't have 651s available so waiting for parts.
I'll continue with it when I have time or feel so inclined, which won't be soon. It's taken up far too much of my time.
I'll continue with it when I have time or feel so inclined, which won't be soon. It's taken up far too much of my time.
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I have now restarted in earnest. I have replaced the 2 bias transistors that now had broken legs from the many manipulations.
I replaced a suspect wire, reassembled the amp and switched it on. Remarkably, no fuses blew, and no smoke was immediately obvious.
Upon measuring the Left and right bias a prescriped, the initial value was 50 mV, and turning up the pot meters enabled ramping up to about 70 mV.
This is obviously not right, but now at least values on both vhannels are equal.
I will continue by repeating the measurements suggested in the previous 7 pages, putting them into an excel and see where they lead. Sugeestions, as always are most welcome.
I replaced a suspect wire, reassembled the amp and switched it on. Remarkably, no fuses blew, and no smoke was immediately obvious.
Upon measuring the Left and right bias a prescriped, the initial value was 50 mV, and turning up the pot meters enabled ramping up to about 70 mV.
This is obviously not right, but now at least values on both vhannels are equal.
I will continue by repeating the measurements suggested in the previous 7 pages, putting them into an excel and see where they lead. Sugeestions, as always are most welcome.
