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Soundcraftsmen A5002 Question

M

madmotoscoot

New Member
I've got a A5002 that was stuck in protect mode. I found a shorted Toshiba output transistor that I have replaced with the same part that I had already. Now both channels work, and I get 325W into 8 ohms. I never see the output transistor rails go up to 93V; they start at 62V and pull down to 58V when in clipping. Shouldn't I see 93V on pins A5 and B5 on the output transistor boards at some point? I checked the rails on the scope, they never go up to 93V.
 
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The 93v rating is for static unloaded transformer voltage. Under load it is brought down below the 63v rating. If it actually did go to 93V, it would be over 1500 watts rms @8ohm!
 
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I sent mine to CBT Audio back in Pittsburg to get recapped since no one seems to know how to work on these in my area! He is also listing Soundcraftsmen repair on Ebay under soundcraftsmen. He takes his time and is well priced looking forward in getting mine back and will post results. CBTAudio.com or Ebay
 
I agree with Avionic, PITA to work on. Rats nest of solid core wire using wire wrap. I've worked on a few of them not my favorite to say the least. It's been a while but I could never find a Service Manual did find the schematic though.

Craig
 
The A5002 is easy to work on. The back screws around the heat-sink end can be removed and there is just enough wire to lay it with the boards still attached and facing up for testing. There is someone selling cd-rom manuals for Soundcraftsmen products for around $10. I bought a copy and it has almost every Soundcraftsmen manual ever made and even some vintage magazine reviews and products ads. But still no bias voltage or dc offset values listed for the A5002 that I can find. I ended up setting bias to 3.5mV on mine.

One of the A5002's I have had many bad caps on the amp boards. 1 board had capacitor C5 bad and caused very low output on that channel starting at Q4 and Q5. Also bipolar capacitor C1 can cause major DC offset problems if it leaks because Q1 sees ground as a positive base to emitter voltage.
 
Forgot to mention those cd-rom manuals I found are on ebay. And that the amp boards on the A5002 have pin connections and push right onto the power transistor boards, unlike the MA5002, which has a bunch of wires connecting everything.
 
Racingh11 said:
The 93v rating is for static unloaded transformer voltage. Under load it is brought down below the 63v rating. If it actually did go to 93V, it would be over 1500 watts rms @8ohm!
Click to expand...
oops, actually its over 500 watts, not 1500. Not sure what I was thinking that day. 93x2=186 x.3535=65.751 ^2=4323.2 / 8= 540.4 watts rms. Still about double what this amp is rated for.
 
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