Question about MCI power supply capacitors

[astroman]

Hey everyone, this may be my first post here. I hope this is in the right sub forum.

I'm working on restoring my JH636 console. Cleaning, recapping, etc.

I've recapped all the IO cards, VCA fader packs, master section, and now I'm moving on to the power supplies.

I'm starting with the light meter supply (mine uses plasma meters and has a seperate PSU for them.)

It has 6 big 40v 20,000uf capacitors. I understand that in most cases, you can use higher voltage capacitors, but I just wanted to make sure in this case that it would be ok, being that the light meters are finicky and the caps are expensive. I can't find any 40v 20,000uf caps, but I can find 50v caps that are the correct size and capacitance. Just wanted to ask and see if these would be ok to use.

Also, just came to the realization that it's going to cost around $1000 or so just to replace the big filter caps in all the power supplies

Any advice would be appreciated.

 

[Brian Roth]

Before replacing those, measure each of the old ones to see if the capacitance value is within 10-20% and the ESR is reasonably low. They might be OK. If not, then going from 40 to 50 Volts rating should be OK.

Bri

 

[Ike Zimbel]

+1 to what Brian says. I would do all of the small caps first. The large caps may be ok.

 

[Brian Roth]

I've dealt with more than a few JH636 desks and seldom had any problems with the big caps in the PSU boxes. But many small caps dried out on the IO modules, especially those in the EQ section that are on the main PCB and "enclosed" heat-wise by the EQ daughter board. It's a bunch of parts including multiple 5532 opamps, all making heat!

Bri

 

[astroman]

Awesome, thanks so much. Yes, as I recapped the IO modules, I came across tons of leaking / bulging caps. Good news on the big ones. I may hold off for a while on those if they measure ok.

 

[Newmarket]

Higher voltage rating is always okay.
Electrolytics should seldom see a voltage near the rating but (all else being equal) a higher working voltage spec increases expected life time.

 

[abbey road d enfer]

Beware that modern lytics have lower ESR than those of yore, particularly if they have a higher voltage rating (I know it's somewhat counter-intuitive, but it's recognized), which may result in increased stress on the rectifiers and/or transformers.

 

[Newmarket]

Beware that modern lytics have lower ESR than those of yore, particularly if they have a higher voltage rating (I know it's somewhat counter-intuitive, but it's recognized), which may result in increased stress on the rectifiers and/or transformers.

Yes ! Things can get too close to perfection

 

[mchelsvig]

I am also rebuild an MCI 636. This has not been used for many years and I am just starting to go through it. A couple of questions. I don't see any bulging or leaking caps but there are loads of Illinois caps on the boards. Can you check the caps in circuit accurately? Also, I know there are some bad 5534's in there. Is there an advantage to replacing them all as long as I am in there?

 

[JohnRoberts]

I am also rebuild an MCI 636. This has not been used for many years and I am just starting to go through it. A couple of questions. I don't see any bulging or leaking caps but there are loads of Illinois caps on the boards. Can you check the caps in circuit accurately?

you can probably tell if they are bad, might not be accurate enough to confirm value.

Also, I know there are some bad 5534's in there. Is there an advantage to replacing them all as long as I am in there?

only if you have too much money

JR

 

[Ike Zimbel]

+1 to what John said. WRT the caps, you can usually check them in circuit with something like the Peak ESR/Capacitance tester. Most of the time you will get a good reading in circuit, sometimes you will either get no reading or a message that says "In Circuit/Leaky", in which case you will need to de-solder one end of the cap to measure it (for axial caps), or remove it in the case of radial caps.
On the IC front, I'm not a fan of wholesale IC replacement, but you will definitely need to have a hard look at all of the IC sockets. If you have the red sockets, they will probably need to be replaced.
Good luck, a 600 can be a beautiful sounding desk once you have exorcised all of the gremlins.

 

[Los Lobo]

Definitely replace the red IC sockets but leave the 5534's and 5532's I've been told the original ones were of very good spec

 

[magic]

The big caps in the PSU's will likely need changing. They work very hard for a living and I have seen them go completely!. Make sure you replace with expensive high ripple rating versions. The big caps on the power rails in the console not quite so important. If you have tantalums in plasma meters get them all out immediately. They go off like popcorn!. As for the rest I would do a 5% rule. By that check out 20 of each value and if you find a faulty one then check another 20. Often you find a specific value that has a high fault rate. I am not a fan of wholesale replacement for the sake of it. You will do more collateral damage to the pcb etc than you improve. if you find red IC socket holders get them all replaced. The best improvement you can get is to replace as many of the old tin plate Molex connectors. They are a big source of the MCI reputation for being munch, crunchy and intermittent. Use gold plated ones from Mouser.