JCM2000 DSL401 hums after replacing rectifier, Help!

KaptinKangaru

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D_hZhogtJHU
https://youtube.com/shorts/D_hZhogtJHU?feature=share
 

PelliX

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Also posted above

Sorry, totally missed them, my mistake. The underside looks a bit of a mess. I'd start by reflowing most of the contacts that look even slightly dodgy there, especially that one of the rectifier. It also looks like one or perhaps two of the pads of the rectifier may have lifted, can't quite make it out. There's also some muck on board, give it a clean with isopropyl alcohol or your cleaner of choice when done soldering. Did the old rectifier test bad?
 

JohnH

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I don't want to harsh your mellow, but I had a 401 that was nothing but trouble for years. The quality of material used in the circuit board is questionable at best. I would re-solder every connection on the board 1st.

I agree with this. I also have thus amp, and due to the heat generated by 8 tubes, all mounted to the board, plus the board material, solder joints can fail and its very hard to figure out

Getting the board out, with keeping control of where all the connectors will go back to, is a puzzle in itself.

But once its out, just work steadily over the whole board reflowing every joint (but with care not to over heat). Better to do all that than to try to second-guess the state of intermittent bad joints.

Only tackle this if you a comfortable and knowledgeabls with working on amps, which i assumw you are

Then get it back together, hoping you can get all wires in the right place!
 

KaptinKangaru

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I agree with this. I also have thus amp, and due to the heat generated by 8 tubes, all mounted to the board, plus the board material, solder joints can fail and its very hard to figure out

Getting the board out, with keeping control of where all the connectors will go back to, is a puzzle in itself.

But once its out, just work steadily over the whole board reflowing every joint (but with care not to over heat). Better to do all that than to try to second-guess the state of intermittent bad joints.

Only tackle this if you a comfortable and knowledgeabls with working on amps, which i assumw you are

Then get it back together, hoping you can get all wires in the right place!
I took tons of pics when disassembling, so no issues with swapped connections.

If some of the pads have lifted, what are my options for repair? Never had to dive this deep into an amp, usually just replacing pots or jacks. Also never burned one off, so no experience with the repair
 

PelliX

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If some of the pads have lifted, what are my options for repair? Never had to dive this deep into an amp, usually just replacing pots or jacks. Also never burned one off, so no experience with the repair

Well, depends a bit on your definition of repair, I guess. Attaching a wire from the component lead to an undamaged section of the trace is a common solution. Technically, lifting a trace doesn't destroy it, of course, it might be lifted and doing just fine. Flooding a damaged trace with solder is another common solution.

On a totally different note, the valve pin sockets look a bit grubby, too - might want to give them a shot of deoxit or whatnot and wiggle something in and out a few times. Tighten 'em while you're in there for good measure.
 

JohnH

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On mine, I patched a couple of areas with some fine tinned solid wire laid over the dodgy trace between pads, then soldered all along.
 

KraftyBob

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I just posted a YouTube video above
It's 120Hz - which is commonly caused by bad filter caps. If the filter cap is not doing it's job it lets some of the 120Hz signal through to B+ which is connected to the tube plates - where it's introduced into your signal.

However, in your amp the hum changes in intensity when you probe the board. Ground loops can also cause at 120Hz hum and if there's a bad ground connection that would make sense if you're pressing on it.
 

tmingle

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It's 120Hz - which is commonly caused by bad filter caps. If the filter cap is not doing it's job it lets some of the 120Hz signal through to B+ which is connected to the tube plates - where it's introduced into your signal.

However, in your amp the hum changes in intensity when you probe the board. Ground loops can also cause at 120Hz hum and if there's a bad ground connection that would make sense if you're pressing on it.
Mine always seemed to cook the joints for the smaller filter caps on the HT chain. The heaters for V1-V3 are dc IIRC.
 

thetragichero

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if the rectifier failed short (which is likely) rather than open there's a good chance that ac voltage reached the filter caps and compromised them so i would be inclined to replace them as a matter of course (along with other suggestions given)
 

KaptinKangaru

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if the rectifier failed short (which is likely) rather than open there's a good chance that ac voltage reached the filter caps and compromised them so i would be inclined to replace them as a matter of course (along with other suggestions given)
Like I'm a newborn, how would i go about testing?
 

PelliX

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Like I'm a newborn, how would i go about testing?

Recitifer is basically just a set of 4 diodes in one component. Test as you would any diodes (your component tester or multimeter may have a diode testing option, otherwise resistance should be inifinite in one direction, near zero in the other). I assume you know how a diode works, right?



Caps is a case of visual inspection first. Bulged, leaking, leaked = failed, dead, gone. If they check out visually, discharge them (you know how to discharge caps safely with a high wattage resistor, right?) and test them with an ESR meter out of circuit. If they test within ~10% of the rating, chances are they're probably fine. Any deviation greater than that, replace them.

EDIT: I feel obliged to remind you, considering that you're asking these questions, that those capacitors can hold a nasty charge that can give you a good jolt or even burns. You've been warned. :)
 

thetragichero

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i wouldn't bother testing the caps and just assume they're bad. unlike the 50s when capacitors were more expensive than big hunks of iron (older amps are wild.... big horkin chokes with like 8uf of filter capacitance), caps are super cheap. especially for a pcb amp like this with radial electro caps, you'll spend more on shipping from mouser (five bucks probably) than you will on the actual capacitors. just be mindful of lead spacing and capacitor diameter. this is just on the dc heaters or was the main bridge rectifier replaced?
 

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