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Sansui G7500 HELP.

Perhaps with the new board it'll be easier to fix this time around?

Sorry this is over my head, just wanna give you words of encouragement. I'd like to see you fix this sucker up, it would be quite a feat at this point!
 
anderslober said:
Parts anyone?????????????????????????????????
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Yeah, bring it with you to New Zealand next time you are this way, I will come and pick it up off you...I will get it going....
Its difficult to work via remote over the internet with a problem like this, its so much easier in the flesh......:thmbsp:
 
I just feel like turning it ON with full power....and then watch it B-U-R-N!!!! ......mmmhhuuuuhahahahhhhhaaaaaaaaaaa..
 
I have contacted the fellow who sold me the board, to see if he can remember anything of importance that could help us out......................

Anyway...Kevin.......flashing dbt......where would you start?
 
anderslober said:
Kevin...shall I put in those 100 ohmers again and turn ON with normal power?
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Well the amplifier seems to oscillating, like somethings backwards or the wrong polarity....
Yeah DBT 100Ω emitters.......it might give you enough time to find out whats happening.....
 
The problem with the board when i had it was that the protect circuit would not release even thought the amp ran ok. bais and dc were correct. The boards protection circuit had been bypassed. Just used it in the garage for awhile.

What doe's DBT stand for? i don't remember it and it doesn't sound like anything i've ever done to trouble shoot amps.

Did you replace the outputs when you put the new board in ?
 
Hey Jeffj7, nice of ya' to chime in. DBT= Dim bulb tester. I have put in all new caps, new relay, tested all tr's....the main outputs are also new(on the left channel). I have tested as much as i possibly can..........there could of course be more............

Did you ever blow any main outputs while you had it(the board)....and if so, which side.?
 
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Anders, are you absolutely sure that you connected the + and - feed wires from the main caps to the correct location on the new amp board? Having the board going into full oscillation while on the dbt may also indicate a solder bridge. How about a new up to date photo?
-Lee
 
Overundr1 said:
Anders, are you absolutely sure that you connected the + and - feed wires from the main caps to the correct location on the new amp board? Having the board going into full oscillation while on the dbt may also indicate a solder bridge. How about a new up to date photo?
-Lee
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Im totally inclined to agree with Lee here Anders........

Yeah, set the camera to Macro and get some nice clear photographs, this was how I eventually found the error on Toby's AU999......
 
If you want more of more specific areas..let me know.
The only mod I did to the board was the bridge(trace was cut) on the trace side.
In the last picture....with regard to the left most blue and brown wires.....on the old board they were as in the picture. On the 'new' board however, they were the other way around. I mounted them as on the old board. This is the PS for the MIC board...+/- 33v.
Confirm if correct.......thanks. I have retracked the wires according to scat....and to me they look OK.
 
Couple of thoughts at this point---
1. both amp boards were oscillating
2. first board came to life then failed after a time
3. second board oscillating

At this point, and I realise that you are probably getting burned out on this project I would suggest the following

After unplugging the unit and bleeding down the main caps (25ohm 8w or similar resistor across the terminals), remove all four of the wires coming from the main caps (red/brown twisted pairs) to the board being sure to tape them off for safety. This allows the board to receive voltage from the power supply however does not supply the outputs. I would also disconnect both pairs of input wires from the preamp (the white and black pair on each side). Tape them off as well. On the dbt try a quick power on test and see if the bulb dims. Let us know.
-Lee
 
Me...burn-out!??.........:-))) You meen wire 17(orange) and 18(red)? AND the black/white preamp wires on the trace side? Will try.............
 
Lee...ok...got the pre-amp wires de-soldered. There are 6 wires connected to the big caps. Orange/red from the ps-board(17/18)......and the orange/red to right channel and brown/blue to left channel. Please confirm........what wires do I disconnect?
 
Lee....shall I just disconnect the 17(orange) and 18(red) pins on the ps-board? this would cut of the power supply to the caps(and the outputs). Please confirm.........
 
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Lee...Kevin.......I de-soldered the pre-amps wires(2xwhite/black) on the trace side and de-soldered the red/orange and brown/blue on the ps-board. I dbt'ed....bright then dim.......very dim................this has got to be good news.............one or more of the outputs are are toast..........is this correct? OR can it be something in the pre-amp? Since it was disconnected.
See photos.......
 
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