Repair shop that can fix an MXR 118 Delay?

[cmdrfun]

Not sure where the right place for this is, or if there is one, but anyway...

A friend brought me an old MXR 118 Analog Delay, the stereo model with the Reticon 5101 chip. When turned on, it has a lot of loud buzz, and the guitar signal is very faint. I don't think there's any audible delay either.

I did some probing with a multimeter and there's power on the board, in ranges that sort of make sense. About 11 V on the power pins of the op-amps. Also used a signal tracer, and I get past the first 1/2 of the first 4558 OK, but then the signal at the output of the second 1/2 4558 becomes very distorted. Problem is, it's like a pile of spaghetti from that point on. I don't have a scope so at this point I think it's out of my league.

So, the real question ... is anyone aware of a repair shop that is equipped to handle these and has had any success fixing them? Or similar stuff, like MXR chorus or flangers, DOD, etc. I thought I would ask before just throwing up my hands.

Thanks for any suggestions...

[theehman]

ronsound.com

[GGBB]

the signal at the output of the second 1/2 4558 becomes very distorted

What's the signal at the input of the second half of the 4558 like?  Sounds like it could just be the 4558, which would be an easy DIY fix.

[cmdrfun]

Thanks Ron, I gave the info to my friend.

My skills are good with building new effects, but not so great with removing and replacing unsocketed chips, and with something of this vintage I really don't want to screw it up, since it's not mine.

[Mark Hammer]

The 118 uses a "tracking filter"  that adjusts the high-end rolloff in accordance with the delay time, so as to get most usable bandwidth for any given delay.

It does this by taking the much higher clock frequency, and using it for two tasks: and dividing it down for stepping the signal through the BBD, and rapidly turning a bunch of CMOS switches on and off to mimic different average resistances in a quartet of 2-pole lowpass filters (2 before the BBD and 2 after).

I'm going to take a stab in the dark here and suggest that your problem may lie in the 4069 chip used for turning the 4016 chips on and off.  Alternatively, your problem might lay in one or more of the 4016s, or 4016 sections, being bad.

I suggest that because the signal MUST go through the CMOS switches to reach the BBD and output, if the 4069 is not turning the switches on fully, of if one of the switch sections in any given 2-pole filter is not functioning properly, you would have less than full signal, and the anti-alias/anti-clock filtering would be poor...which is pretty much what you are experiencing.

This would be true regardless of which particular BBD chip the issue in question was using (5101, trio of SAD-1024, SAD4096).