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Optomica sa5151 no bias 0mv

O

Oscar23

Active Member
I have an optimica sa 5151 when I got it it was stuck in protection I changed the outputs with mj21193/94 replaced 2sb649 and 669 with KSa1220 and ksc2690 and some fuse resistor the amp now comes out of protection but the one chanel is very low barely able to hear it and the bias is reading 0mv
 
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No bias at all 0 MV it does come out of protection it didn't before how do I test a transistor at the junction ?
 
the voltage readings will help if you can do it safely with a clip on probe . or probe taped up right to the end so tiny bit showing that cant cause short circuits .
black - probe to chassis ground .
 
Ok I've never done it live always wanted to figure out how to do it safely thank you so just use the reading on the as schematic
 
interesting design of this amp .. am more familiar with regular ab amps . those voltages when you get them will a tale .
 
It's built like a tank huge I've never seen an amp built like this. So much room and weights a ton. I figured the space would make it nice to learn on
 

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Well I finally got the new outputs and those voltages
502 b 50.5v
C .5v
E 51.5
504 b -51
C -.3
E -51.5
509 b 0
C- .3
E 0
510 b 0
C-51
E 0
Any help would be appreciated I'm at a loss
 
quick look says you are at least missing collector voltage at q509 should be about 51v by the looks of it .maybe a broken trace on the board
 
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