Picked up another project about a week ago, Krell FPB-200 that had 1 channel distorting at elevated volumes.
Immediately after winning the auction I made my parts list for a full recap. Once the amp showed up I inspected it for damage and hooked it up to verify the previous owner's description.
Powered up fined no issues, at about 25% volume the left channel would begin to distort. Once the parts showed up I removed and replaced both channels capacitors. Reassembled everything and hooked the equipment back up only to have the circuit breaker on the rear panel will overload sitting idle. I have taken both channels back apart and inspected all of the solder joints and correct orientation of electrolytic caps and checked about 60-70% of the caps with an esr meter 2 different times.
Does anyone have any ideas on what to check next? It is obviously a self-induced failure but for the life of me, I can't figure it out.
Oh just to ensure something weird hadn't happened to the input power board I hooked power to it without the transformer outputs connected to the driver board and it didn't overload the circuit breaker.
Immediately after winning the auction I made my parts list for a full recap. Once the amp showed up I inspected it for damage and hooked it up to verify the previous owner's description.
Powered up fined no issues, at about 25% volume the left channel would begin to distort. Once the parts showed up I removed and replaced both channels capacitors. Reassembled everything and hooked the equipment back up only to have the circuit breaker on the rear panel will overload sitting idle. I have taken both channels back apart and inspected all of the solder joints and correct orientation of electrolytic caps and checked about 60-70% of the caps with an esr meter 2 different times.
Does anyone have any ideas on what to check next? It is obviously a self-induced failure but for the life of me, I can't figure it out.
Oh just to ensure something weird hadn't happened to the input power board I hooked power to it without the transformer outputs connected to the driver board and it didn't overload the circuit breaker.
Why replace capacitors before doing fault tracing? Now you may have two faults: the original one and a new one you have inserted while changing caps.
Make a lamp limiter. Check DC voltages, comparing the good channel with the bad channel.
Make a lamp limiter. Check DC voltages, comparing the good channel with the bad channel.
I did, that was the initial reasoning for powering the amp to verify operation, in hindsight I WISHED I would have only re-caped the left channel first! I have just finished going over my work a third time with a magnifying glass, found a couple of iffy solder joints.
Yeah, I am kicking myself for doing both channels at once!
Yeah, I am kicking myself for doing both channels at once!
Tried hooking the channels up one at a time last night and couldn't get either one to trigger the circuit breaker. I ended up hooking both channels up again and it would seem the problem has gone. Yesterday I fixed the 3 or 4 solder joints that didn't look right, to much solder. I also removed two caps that I thought I had possibly overheated and tested them outside of the circuit. This has me scratching my head. Tonight's goal will be to hook the frequency generator and o-scope up to begin testing the amp. If all goes well I may actually be able to put the Krell back into service and pull my two Audire Forte amps out of the system for a rebuild.
analog_sa,
I began the thread asking for ideas and what I have received is nothing close to helpful ideas.
Not that you would know but I actually have formal training, I provided a link to give you an idea of what was involved in recertifying.
Naval Sea Systems Command > Home > RMC > MARMC > 2MMTR > 2M Technical Recertification
I am sure you have never installed a component in backward or removed the wrong component by mistake, I have, that is why I check and re-check my work, I know I am not perfect. I have 30 years of experience in electronics and I still learn tips and tricks from other peoples experiences.
Interesting how you phrased "botched recap job" but offered no real advice or help.
I am an audio enthusiast, I love building or repairing things I know I could normally afford or justify spending
Please troll someone else's thread if you have nothing share.
"Yesterday I fixed the 3 or 4 solder joints that didn't look right, to much solder"
That's 30 years of experience speaking, right?
Using proper tools/techniques it should be impossible to tell a solder joint has ever been redone, let alone leaving a mess that actually shorts something.
What advice could you possibly expect?
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