Korg Maxi-Korg 800DV / Univox K3 part 3: Capacitor replacement

Electrolytic capacitors go bad eventually, Maybe not tomorrow, maybe not next week, but eventually they go bad. If I was a tech fixing this Maxi-Korg on a budget for a kid who just dragged it home from a garage sale I would probably insist on recapping the power supply and replacing the tantalum capacitors, doing some testing and sending her on her way with a $60 repair bill and a few words of encouragement to take care of this neat thing she is now the keeper of.

That is not the situation. I am a guy who likes to do it once and do it right as much as possible. I am going to replace all the capacitors. Top to bottom, inside out – even the couple of tantalum caps tacked onto the back of some of the sliders. And why not there’s only like 60 or so.

I did mention it was all apart right? The 800DV is two 700-Ss under one roof with a nice complement of controls to blend the two. The two boards on the left are one 700-S, the two on the right are the other, and the board in the middle is the blender. Those big black squares are the potted “IC”s. A lot like the early Yamaha dudes found in a GX-1.

Once you have decided to replace all the capacitors in something, you might as well get on with it and put an order together. The easiest way to put your list together is find someone who has done the job before and ask them for their list. This failing, you will have to make your own. My method for making a list is to find the service manual and see if it has a decent parts list. In the case of the Maxi-Korg – sort of.

SB049 – the blender board has a parts list here. 3 tantalum capacitors and 2 aluminum electrolytic capacitors. No Problem! Notice the inconsistent naming here. Parts list has SB049 where diagram has SBC-049.
The parts list has 5 capacitors. If you were to spend 15 minutes methodically looking this board diagram over you would find that there were actually 19 capacitors, one of which is a 10uf 16V. This one is not on the parts list.

I ended up spending about an hour and a half looking over print outs of each circuit board and tallying up the caps on them. I have to replace 82 capacitors! I should mention that you replace tantalum capacitors with electrolytics of the same rating. Upping the voltage within reason is fine.

My next move is to review the list and see what sizes I can combine to try and order more in bulk. You can up the voltage of a cap without issue within reason – reason being say 3x or less. For example there are a few 10uf 16v tantalums and several 10uf 25v electrolytics. These call all be replaced by 10uf 25v caps.

Once I have this rationalized list together I go through my capacitor stash and see what I have on hand so I can get started right away and avoid hanging on to capacitors too long. In the case of this rebuild I had the 100uf 50V, 1uf 50V and 220uf 25V capacitors on hand.

This picture looks weirdly distorted. The light green and black with gold stripe capacitors are from the ones I had on hand. The two rusty brown orange things that look like little balloons are the tantalum capacitors.

I placed my order with Mouser on a Monday and had my box of capacitors on the following Saturday. Some pointers ordering from Mouser: Round up to the next price break if possible – many times you will get twice the number of capacitors for 25% more money and the extras will help you out on a future project. Buy bulk rather than ammo pack or tape reel – the extra time cutting each capacitor from the tape adds up! Think ahead to the next project so you can save on shipping – I ordered all the capacitors I need for a 1968 Fender Bassman 50 I got recently and I don’t think shipping cost me any more.

Here is the power supply board. Seven capacitors need replacing. These mauve capacitors are high quality, but quality is not the issue, it’s age, and in the power supply the caps see a lot of action!
Twenty minutes later the power supply is all redone. I’m sure I’ll be back in here adjusting the voltage before long, but mission accomplished with the caps. IC are Illinois brand, the black ones are Nichicon and the green one is a Xicon. Most people prefer the Nichicon brand, but they don’t make a lot of axial capacitors (leads out of both ends), and most people consider Xicon a cheap capacitor, but I inherited a bunch and have used them without issue. I didn’t get a picture of it, but there is a heavy duty metal cover for the power supply with a bunch of M3 nuts serrated on the ID washers that hold it down to the copper plate,
This is a big milestone. All capacitors, with the exception of a single 2.2uf 25v fellow that I somehow missed on my order have been replaced.

Up next: probably the control panel, but maybe some cosmetic work on the wood or metal panels.

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