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2SK30 20th July 2008 11:59 PM

problem with old reverb - help?
I have an old Ibanez Reverb unit. I believe it was manufactured by Sony. The trouble is that it makes horribly loud snaps, pops and noises like firecrackers. I know whatever the problem is is before the reverb DSP because it gets reverbrated with the signal. From the input I see a few opamps, electrolytic caps, what looks like a small transformer or relay, a very strange chip that is labelled 'LPF' on the board, and resistors and such. I have tapped the board and looked to see if something might have a bad solder joint but haven't found anything.

Any idea what component could go bad that would make pops and snaps in the input? Could a bad cap do this or is probably a semiconductor?

leadbelly 21st July 2008 04:28 AM

I would look at all the pots first, they are most likely the cause of such noises. Don't limit yourself to the input side, as the reverb could work by analog regen, and if it did, components on the output side could cause the same symptom.

2SK30 21st July 2008 06:11 AM

How would pots make firecrackers noises without being touched? I poked around the board with a multimeter. If you test resistance of an electrolytic capacitor what would you read? Most of them were very low except one which was infinite. I don't know if that means much but I suspect it is a bad cap that is doing this.

Mooly 21st July 2008 04:20 PM

A couple pointers-- You can not read an electrolytic cap on a DVM reliably let alone with it in circuit. An AVO 8 yes!! (But only out of circuit) The slightest charge on the cap will totally confuse the DVM. Small ceramic disc caps can give trouble occasionally, becoming intermitantly leaky. A very strange chip ! LPF Low pass filter perhaps -- it may not be a chip in the sense you think.
Is it heat related -- try freezer spray very sparingly.

2SK30 21st July 2008 08:11 PM

Oh I was checking it with the power off and the caps discharged I was trying to check for shorts but I'm not sure how to do it.

I think it is heat related because it doesn't happen until the unit has been on for a while and then it is like a firework show in a reverb and echo chamber.

Don't know I might just throw it away and get a new one it is vintage and is a fairly good reverb but if I bring this to a tech it'll cost me $70 just to look at it and I can get one on ebay for $100. I was hoping I might be able to fix it but it is a very dense circuit and I have no idea where to look. I checked the obvious things but don't see anything really noticeable.

Mooly 22nd July 2008 10:56 AM

Freezer spray may help. Use it so sparingly that it just "dribbles" from the straw onto a particular part.
Even switched off there is enough residual charge around -- it takes only a few millivolts -- and the DVM readings are meaningless + any semiconductor junctions totally confuse things.
Could it be power supply related, are there any regulators that get hot -- things like this are favourite for dry joints particularly on Sony TV's etc. Not always obvious either. Check it out !!

Post a picture of it inside if you can.

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