Analog delay dying : help!

Flanging_Fred

Can any of you clever fx folks explain what might be going on here? 

I have an an old and much loved Arion SAD1 analog delay which is a lovely sounding thing but has started playing up.  If I power it up and plug it in after a long period of not being used, it plays fine and sounds as good as ever. However, after a period of about a minute or so,  the delay signal gets distorted and the volume of the delays fades out to nothing. If I unplug it, leave it a few days, then when I plug it in, the process starts again.

So can anyone tell me what is going on here? I suspect something to do with caps but I’m not sure.

Would this be fixable for a reasonable cost? I’d love to get it working again...

thewitchcrafter

Ei Fred. It sounds like it is power related, but it could be anything really, corroded traces, bad Electrolytic caps...
Have you tried with a battery?
I make guitar pedals for a Manufacturer in London and make some pedals on my own time and also fix and mod. If you can't sort it out yourself I could have a look for you. If you feel comfortable with a soldering Iron and a DMM, I could try to assist you. 

ICBM

Sounds like a bad electrolytic cap. If there's one in the signal path that's leaking, it will allow DC to slowly build up on the preceding or following stage, which will get progressively more distorted and then cut out.

If it is that it should be very simple and cheap to fix - the only issue will be identifying which one it is, and there shouldn't be too many possibilities. At worst, simply changing all the caps should fix it and might be the best approach anyway given the age of it.

If it's the delay chip it will be more expensive though...

ThorpyFX

As others have said, sounds like an electrolytic that’s failing. Easy fix if you need it doing. 

Flanging_Fred

Hi, thanks for the replys. I did try with a battery and got the same result. 

I can solder cables and pots etc but haven't really tried a PCB beyond fixing dry joints. I have a copy of the schematic so is this an operation someone can talk me through? I also have a digital muktimeter but am not sure if I can use that to check through the caps and see if they have failed. I opened it up but can't identify any bulging ones.

Maybe it would be better to pass it someone with more experience as I really don't want to mess it up.  

ICBM

If you want to have a go yourself, the simplest thing to do is replace all the electrolytic caps. I doubt there are more than a dozen. Make sure you use the same values, at least the same voltage rating, and observe the polarity.

Replacing electrolytic caps at 30+ years is good practice anyway, so even if they aren’t all faulty it will do no harm. I would guess there’s a more than 90% chance this will fix it.

thewitchcrafter

Like ICBM says, replacing the Electrolytic caps will be good practice and quite likely you'll fix the problem.Take notes of the values of each one and get replacements for those parts. Anything rated higher than 16V. IF possible, take some pictures of the insides of the pedal so that we can try to identify something obvious.

Flanging_Fred

Not sure how how useful this will be, but here it is...

ICBM

OK, a few more than I expected, I can see 20. It's hard to guess which one it will be causing the problem, although it won't be the grey 220uF next to the LED, that's the main power supply filter cap. It's not even easy to work out which the V/2 cap will be, it could be almost anywhere! The other grey one next to the switch is a possibility since it's probably also a large value.

Flanging_Fred

Update...

So I took the plunge and had a go at replacing the caps, which I've never attempted before.  I spent Saturday afternoon soldering (as I'm new to this it took ages).

Anyway I finally found a 1uf that seemed bad. I changed it over and got my delays back but they were still distorted so I thought I had better go through and change all the caps.

Rookie mistake.

Now it doesn't work again

Arse biscuits.

I just want to throw the damn thing in the bin now...