Laney BC 75 schematic ?? Any one have a copy ??

[Smitty02]

I got a Laney BC 75 solid state bass amp That has no output, power supply issue, one of the 2 4700uf caps was rolling around on the inside. Some one has worked on it before me and replaced many transistors. I replaced the cap yet I got a dead short some where. It blew my light bulb current limiter in about 10 seconds. It is a basic layout but I could use a schematic to check what was done to this thing before I got it. The bridge rectifier tests ok but i suspect it may be a issue under power Thanks

[DrGonz78]

Try this one out>>>
BCRange-BC75included.pdf

Look at pg6 for the power board and I think pg5 was the preamp??

[Enzo]

And look for shorted output devices.

[Smitty02]

Will do Enzo ...Thanks for the schemo DrGonz, now I can check and see if they used the right stuff in there. Much apprecieated Time to dig back in

[Jazz P Bass]

Can somebody clue me in on how they are pulling 120 watts output with a + - 44volt power supply?

[g1]

Can somebody clue me in on how they are pulling 120 watts output with a + - 44volt power supply?

With 4 ohm load, only 22V RMS is required for 120W, that would be about 62V peak to peak, +-44V should allow for more than 62Vp.p. am I missing something?

[Enzo]

120 watts from a single pair of output transistors is asking a lot. At least from a reliability standpoint.

[Smitty02]

I went through it with the Schematic DrGonz kindly posted, someone had worked on this before i got it and replaced all the transistors and such, when I got it it had one of the 4700uf caps rolling around in it. They used all the correct parts the outputs were mj15003's though not the 2n's but compatable. As I said when i posted it lit up my current limiter big time After going over all the replaced parts and re-soldering, one of the power transistors TIP32 I believe was bridged I put the old cap back in it fired it up and it was good to go took it off the limiter and ran it into a 410 8 ohm load and it sounded fine, actually not bad for what it is, and cheaply designed ( nothing holding the board up but the jacks and the 2 heat sink screws ) it thumped pretty good I checked the the voltages 38 & -38 they were one volt shy at 37 then I checked the A & B points which were high but I could only get them down to 11.9mv. . I played it for bout half hour heat sink got a little warm, caps were cool.. seemed to be just fine it is a 1 15 combo and probably should stay at 8 ohms. But road tested well to me , out the door it went... Enzo I did pass along your info to the Lad with the Marshall VM, it is a youngsters and he is cash strapped Im told, this is why I was told to just fix the fx issue though it needs new KT66's and a going through. I left your info and strongly urged him to see you in my write up, but I dont think he has even picked it up yet. I hate when guys say "just do this" when you see it needs some tlc....But I does what I's told