Help me swap the power capacitors in my 1975 Minimoog!

[v8media]

So, I wrote way too much on this (link below, which includes photos), but the gist is, does anyone have a 1975 (or thereabouts) Minimoog with power board 91-118 with 3 capacitors on the board, vs the 2 that I am seeing in every photo, schematic, and board scan? Or do they have that board with 2x capacitors, and if so, what are the values and what is connected where on the bottom of the board?

Everything I'm seeing has 2x 470uF caps. When you're behind the Minimoog with the case open, the capacitor nearest you is + to the right, the further one is + to the left. That matches the markings underneath my board.

However, mine had 1x 470uF +left further from you, and 2x 1000uF closer to you, as well as a jumper wire underneath the board. Unfortunately, I wasn't paying enough attention when I pulled those out, but my guess is they were both + to the right. I know 2x 1000uF in series makes 500uF. I believe I really just need confirmation that I should replace the 3 capacitors with 2 470uFs. I'd love to find a board scan for this specific board, and/or photos of one of these boards fully pulled out of a Minimoog, as I really don't want to have to detach mine from the main wiring in order to look at this more closely.

The other tidbit is that the replacements are specced at 63V vs the original 50V. Does that matter in any way?

More info: http://v8media.com/minimoog/index.html

Thanks very much for any help or info!

Ian

p.s. - I would love to have this working soon in order to photograph myself and my Minimoog celebrating the 10th Anniversary of the Minimoog Voyager!

[thealien666]

I have a 1975 Mini with 3 capacitor rectifier board. Here's the schematics:



Here's what it looks like in mine:





Replacing original caps with higher voltage specs on new ones is okay, as long as the capacity is the same.

[Kenneth]

Wow, Alain, you sure keep the guts of that Mini spick and spam! Looks brand new!

[thealien666]

I vacuum the insides of it every week !

Nah, I'm kidding of course.
I cleaned it only once when I bought it, and it wasn't very dusty. Only very damp, with a mustiness that took forever to dissipate...

I call those three electrolytic caps, in the photo, the "three little pigs"...

[v8media]

Ah, should have noted that it wasn't like that one. I've seen that schematic before, but hadn't seen a photo of that one. My board seems closer to the boards with caps rotated 90 degrees from that, but only with two caps vs the three in mine.

[thealien666]

AFAIK there were several revisions of that rectifier board. Maybe Kevin Lightner has possibly seen them all ?

[Kevin Lightner]

Facing the rear, the cap closest to the panel has the + on the left.
The cap in front of it (closest to you) has - on the left.
Same as in the photos on your page.
Are we missing something?

[v8media]

I'm not at my place, I'll have to take a photo of it later tonight. It's definitely different than this example or the two caps facing the other direction. My guess is that it's a hack, or Moog was out of enough 470uF caps so replaced one with 2 1000 uF caps.

Edit: actually, I had taken a photo previously, so here's my board currently, but since it's 3 470uF in the place where most of the boards with this orientation have 2uF . . .

That photo should be attached now.

[Kevin Lightner]

Moog did make several versions of the rectifier board.
They started out with two caps (470 or 500 uf), then went up in value and number.
Late Minis made had either two 1000ufs and a 470uf or all three 1000uf.

It's very likely there are board markings on the underside that say + or -, but it shouldn't be too hard to figure out from the schematics.

[JohnLRice]

As long as you are in there replacing the caps you might want to replace all four diodes. Normally i wouldn't suggest this but many years ago my Mini quit powering up and it turned out that 2 of the four diodes had died. Might as well replace them with fresh ones as long as you have it all apart?

[Kevin Lightner]

While I don't disagree with the replacement of the diodes, they're polarized too and I think he's gotten himself in enough hot water trying to do the caps.

[JohnLRice]

While I don't disagree with the replacement of the diodes, they're polarized too and I think he's gotten himself in enough hot water trying to do the caps.

heh, I hope not but, it is easy to do it wrong! (something you don't forget soon though! )

I hope you are well, Kevin!

[v8media]

I guess I'd have to find a copy of the schematics for this board version, or possibly a photo of a similar Minimoog. Are the capacitors in all variations of Minis going to aim for the same section of the power board? Will tracing out and comparing a schematic for one that doesn't match mine possibly help me out? Or will something else in the overall wiring layout have changed as well?

Unfortunately, there are marking on the underside, but not for all three capacitors. The markings on the underside make it look like they intended to put 2 capacitors there, with the closer one + right, and the further one + left. Mine had the closer two both connected to the same point on the right.

I probably will replace the diodes, but I definitely want to figure this part out first.

Thanks for the help!

Moog did make several versions of the rectifier board.
They started out with two caps (470 or 500 uf), then went up in value and number.
Late Minis made had either two 1000ufs and a 470uf or all three 1000uf.

It's very likely there are board markings on the underside that say + or -, but it shouldn't be too hard to figure out from the schematics.

[Kevin Lightner]

I think Moog added the third capacitor to earlier boards as they still had stock of them.
Later they designed a rectifier board featuring the three caps in a row.
Electrically there was no difference from one with a cap added.

Perhaps it's me, but I just don't quite understand what the problem is.
This is a very simple circuit and IS shown in the service manual.
There's one cap across the positive rail to ground, one cap across the negative rail to ground and one cap that goes across both rails, + to -.
The polarities should be obvious.
Is it just that you want it to look stock like a later rev?

[v8media]

I'm not the most electronic of people, and since my Mini wasn't matching the documents I have, I had to figure out why. Your description was helpful though. I'll try to finish that up tomorrow.