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Onkyo M-5030 keeps blowing

twoAcestwo8s

twoAcestwo8s

New Member
I have an Onkyo M5030 that I recently acquired from a friend. I recapped it but when I went to turn it on it was at first stuck in protection mode and then the main fuses blew. I replaced the fuses but again they blew. I'm not sure where to begin, I'm still fairly new at diagnosing and repairing amps but I want to get this thing working again, any help would be appreciated. Apologies if this post is in the wrong place, new to AK, I'll be happy to repost in the correct section if need be.
 
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Welcome aboard Aces
Double check your work for solder bridging and capacitors installed correctly.. Did the unit work before you started ?
 
I did use my multimeter to check for shorts due to bridging. The unit was in protection mode prior to me recapping it. I will reach out my friend to see if it ever worked for him.
 
Check Q416,417,418 and 419 on both amplifier circuits. For possible shorted junctions.
 
Checked the transistors you mentioned, 2 on each side we're bad Q418, Q416 and the respective two on the other amplifier circuit, Q518, Q516. I'm also seeing a bunch of shorts across the resistors connected to the transistors you mentioned, I don't know if that's bad or not.
 
Oh okay cool, that's good to know. I ordered parts to make a DBT and I found replacements for the transistors and put in an order: 2SC4468 and it's compliment 2SA1695. Still waiting for my friend to get back to me. In the meantime is there anything else I should check?
 
Small update and another question while I wait for parts: my friend got back to me about the amp. Turns out that he took apart the amp to clean it and when he put it back together he accidentally swapped the two cables that go from the meter pcb to the power supply pcb. When he turned it on he saw smoke. He quickly unplugged it and eventually he noticed his mistake then corrected it but by that time the amp was stuck in protection mode :rolleyes: So I grabbed my meter and did some exploring around the area he said he saw the smoke come from; long story short I found a shorted diode (D124 in the service manual) that was preventing the associated relay from working. In terms of replacement, the service manual says its a 1S2076TD, I reallly don't want to put in an order on mouser/digikey/etc. for just one part, so can I get away with using a 1N4148(I read some other posts about that being okay, just wanted to confirm)?
 
Another update, all my parts came in! Built a DBT and I replaced the faulty output transistors. However when I turn on the amp (plugged into the DBT) the bulb turns on bright which usually means a short somewhere right? I grabbed my multimeter and started with the transistors, the entire left channel, all the output transistors Collectors are shorted to ground. I just replaced the output transistors so I don't think that's the problem, something somewhere else is causing the short, I'm not sure where to begin however, what do I look for?
 
twoAcestwo8s said:
Built a DBT and I replaced the faulty output transistors
Click to expand...
tip: you can test using the DBT w/o installing the output transistors.
Might be able to desolder/ gently lift the leads of the O/transistors to test vrs pulling. also testing the transistors.
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edit: just to add don't use dbt to check/ set bias. must be done w/full power.
 
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