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Rockola 48350-1A amp blows main fuse


robm

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Hi All,

 

Picked up an old Rockola 463 that had rat chewed wiring and a blown amp.

 

Repaired all the wiring, and the machine will select a record and spin the turntable, however if the amp is plugged in, it blows the main fuse (not the fuses on top of the amp, the main machine fuse).

 

I have pulled the amp out, and really don't know what i am looking at - any suggestions on what to test or shotgun replace? I can use a DMM, but do not have an ESR or oscilliscope.

 

Will throw a few pics up of caps that look suspect to me and are prob worth replacing as a starting point.

 

Any suggestions are welcome!

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IMO, I would start with replacing all electrolytic caps, there's one in the bottom pic that is an example of bad cap.

Any expansion at either end is a sign of 'due to be replaced'.

Whilst your at it I would be looking/checking resistors too, and, if any caps have leaked onto the circuit board/s, check the traces.

The mains fuse that is blowing, that you are replacing.....is it correctly rated?

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IMO, I would start with replacing all electrolytic caps, there's one in the bottom pic that is an example of bad cap.

Any expansion at either end is a sign of 'due to be replaced'.

Whilst your at it I would be looking/checking resistors too, and, if any caps have leaked onto the circuit board/s, check the traces.

The mains fuse that is blowing, that you are replacing.....is it correctly rated?

Yep. 5a as marked on panel

 

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Also check if there is a mains filter cap, maybe the large can one on the LHS. If this has shorted the mains fuse will blow. For a process of elimination you need the mains filter cap there. You could remove it if in doubt.

You can test a capacitor out of circuit with multi meter. Discharge the cap first but shorting the legs on a metal surface, like a vice, set MM on a high resistance and attach probes, you should see the meter resistance reading increasing slowly.

If that is the cap and you want to keep it looking original you might be able to remove old connections and replace with a new smaller in size cap inside the housing.

Upon reading your first post I now see it only happens when you plug the amp in, my bad.

You have tried going bare bones?

Nothing connected then one at a time adding connectors? Guessing you did this to determine it is the amp causing the fuse to blow?

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Also check if there is a mains filter cap, maybe the large can one on the LHS. If this has shorted the mains fuse will blow. For a process of elimination you need the mains filter cap there. You could remove it if in doubt.

You can test a capacitor out of circuit with multi meter. Discharge the cap first but shorting the legs on a metal surface, like a vice, set MM on a high resistance and attach probes, you should see the meter resistance reading increasing slowly.

If that is the cap and you want to keep it looking original you might be able to remove old connections and replace with a new smaller in size cap inside the housing.

Upon reading your first post I now see it only happens when you plug the amp in, my bad.

You have tried going bare bones?

Nothing connected then one at a time adding connectors? Guessing you did this to determine it is the amp causing the fuse to blow?

 

yep - started with only the transformer connected, then added lights, mechanism, slector plugs, and only when i plug in the amp the fuse blows

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I personally wouldn't be going any further until all electrolytic caps are replaced and checking each circuit as you go.

If a cap has shorted instead of going open there is trouble.

As rodents have been in there I would be looking for any continuity to ground that shouldn't be with your MM.

Rodent piss is very corrosive, I have seen the damage it can cause.

Do you have a 5A resettable fuse you can put in the circuit to save replacing fuses?

The front panel where adjustments are made looks to connect via edge connector plugs, I realise this means if you try it and it still blows it's another fuse to replace but have you isolated it also?

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I don't have a resettable fuse that suits the barrel type holder.

 

Will see what caps i have, but pretty sure i wont have all of the repquired ones on hand. Yep - could remove all the front panel plugs to isolate the issue by half!

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Could you solder one onto a blown fuse that does fit?
Not sure. Since the wiring is inside the panel it's a bit tricky. But could if I opened the panel up I guess.

 

Now the machine is tripping out the rcd.... With only the step-down transformer connected.

 

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any update on your juke @robm ?

 

Thanks for the bump. I am having some more issues with it, as it blows the RCD in the shed most of the time, with only the transformer connected, so really need to confirm that is an issue, then maybe source another transformer. I've got a few other things on at the moment so this will liekly take a back seat for a while.

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Is there a line input filter on that model? If there is, chances are that's what is shorted & not your transformer.
Nah. I was hoping that be the case but no filter

 

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Rob I have a Rockola 473 that has same amp as yours. I have it in the shed at the moment trying to fix some issues with the selection system but everything else works. I am very green on jukes but if you need any pics to compare with let us know.
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Rob I have a Rockola 473 that has same amp as yours. I have it in the shed at the moment trying to fix some issues with the selection system but everything else works. I am very green on jukes but if you need any pics to compare with let us know.
Awesome. Thanks for that. Yep first time I have ever looked at one as well!

 

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