Cool "rare" guitar and radio problem!

[Cliff Schecht]

A buddy of mine picked up an all original Gibson RD 77 Artist (http://en.wikipedia.org/wiki/Gibson_RD) at a great price the other week. The guitar was essentially unmolested and had all of the original crap that came in the case.

The first thing I noticed when we plugged it into an amp was the radio that could be heard and the really high noise floor. The guitar was practically unusable with any sort of gain. My first attempt at fixing the radio (and noise) was to get down into the circuit board and replace the electrolytics with fresh ones of the same value (about 20 of them on the board..Damnit Moog should have used tantalums!). This killed most of the noise problems but the radio is still very persistent.

To be more descriptive, the radio comes through not very clear, it's buzzy and distorted. The active treble control can boost or cut the radio and the compressor can really kick it up a notch and so I think the radio is originating very early in the circuit. Just probing around with my finger doesn't ever kill the radio.

The next logical step to me is to start replacing the IC's (using sockets). I've had luck with SS stuff before where the digital stuff (in this case a CD4016 IIRC) wasn't soldered down well and was causing radio. But I'm very hesitant to start changing out more parts in a guitar that is so valuable without knowing for a fact that the problem will be fixed.

FWIW I did pull the pickups off of the PCB and tested them by themselves. They are microphonic as crap (especially the bridge) but don't pickup radio on their own. I'd like to pot the pickups but again, I don't want to hurt the value of this guitar too much in case my bud doesn't want it later.

The most annoying thing to me is that when he plays this guitar through the Rocket I built for him, I can hear his radio IN MY EXPRESS! At that point I made him put the guitar away .

So I'm not sure if I want to keep working on the big PCB and try to fix the problem or just pull the big PCB and make the guitar passive (literally have to desolder one wire to do this). I'm not afraid of the PCB work, I'm very competent with PCB rework, but I don't want to hurt the value of the guitar. IMO it's not worth as much if the electronics don't work but the vintage market is a fickle beast..

[Structo]

Man, I haven't seen one of those in years.
Got any pictures?

So are the IC's already socketed or is it your plan to install sockets?

Is everything oxidized?

How about a small pf cap across the input? (like 10-15pf)

That's what I do to amps that are RF sensitive.

[Cliff Schecht]

Yeah I'll dig up pics in a bit.

I was going to install sockets. Of course they aren't socketed .

Some of the IC's and transistors are oxidized but the solder joints are all intact. I didn't find one that needed redoing. It's obvious they took some pride in building this guitar.

Put the cap across the input of the amp? The amp doesn't do the RF thing with any other guitar and the guitar plays radio through whatever you plug it into. Do you mean put a small cap across the guitars output jack?

This makes me wonder if a small cap across the pickup connectors would help (from hot to ground)..

[selloutrr]

Grounding wire to the bridge is probably floating.
I have a '79 RD Artist bass in the collection. it sounds great but it's just heavy ... Over (18lbs) The Artist model was equip with moog active electronics. The RD standard was passive. Originally designed to be etwhistles signature model bit never endorsed production ran from '79-81 reissued in 2012 as a noveselick signature model for the epiphone line. The guitar was based around the bass artist series which included a Les paul, 335, RD and victory model.

[Structo]

Do you mean put a small cap across the guitars output jack?

This makes me wonder if a small cap across the pickup connectors would help (from hot to ground)..

Yes, it takes the radio frequencies to ground.