New to the X68000 scene. Attempting to repair XVI / PSU.

[SkyeWelse]

Hi everyone,

I'm not exactly new to the forum, I just mainly hang out in the PC-98 section mostly since that and MSX are my main Japanese computer hobbies. I've always wanted to get into X68000, so earlier this year I bought one off of Yahoo Japan Auctions that needed some repairs.



It would at least power on and one of the drives seemed like it was trying to operate normally, but I wasn't able to get video out even though I used a  D-SUB-15 to VGA adapter that I typically use for my PC-98 which works like a charm. Also I couldn't get any disks to load or hear any sounds, or see any LED lights turn on the keyboard when the keyboard is plugged in. I'm not at all used to X68000 machine, so I'm not sure if these are things that I should be seeing/hearing at this point, but I decided to take it apart and recap it. If anyone is more curious as to the behaviors it was doing before I attempted to do the cap replacements, I did record a youtube video for a friend to see who sometimes does repairs and modwork, but he lives pretty far away from where I am in Georgia.

My repairs included the following:
1. Replaced caps on PSU
2. Replaced caps on Video board
3. Replaced caps on Motherboard
4. Replace Coin Battery on Base DaughterBoard? What do you all refer to this board as out of curiosity?



After recapping the PSU, I tested with a PowerBright 100J StepDown converter that uses a 2amp fuse. I use this with my PC-98 machines, MSX machines, and my X-RGB3 to power them up with only 100 volts.

No fuses blew. No issues I could see with caps exploding. I then put the PSU back in metal case and tested again. No fuses blown. Again no issues. I then put the PSU back into the X68000 XVI and cut the power on and the XVI powered right up and showed the 10Mhz light on (since it was on that mode with the switch) However, this process emitted a very loud high pitch frequency for about a minute, and then the fuse blew in the Step Down converter and the system powered off gradually with loss of power not being supplied to it. (I.E. 10 Mhz light dimmed and then went off)

Ever since, the PSU now blows a fuse in the Stepdown converter anytime I turn on the PSU. This is likely a short, only I cannot for the life of me figure out where it is.

I've cleaned and resoldered some areas that I thought the solder could have been better and had a friend who does computer repairs for years take a look at it with me. We can't determine where the short is, but we estimate that some of the components in the middle of those boards may have gone bad or the short is there perhaps but without being able to provide much power to that section since the fuse dies instantly in the stepdown converter when powering on, so it's hard to find out where power is getting to exactly.

The next step was to try and order some replacement parts and try to find a picture of what a good working PSU underside looks like so we can see exactly where the solder points are and if any are perhaps touching or making a connection where they shouldn't be. I could be wrong, but I believe after comparing a PSU for the Expert and the PSU for an ACE, the PSUs are similar, but not exact. From what I can see on this site (http://kpark.co.kr/3022570), a PSU for a SUPER is the exact same as what is used in the XVI.

If it's not too much trouble, is there anyone here who can show me the underside of either a SUPER or XVI PSU that has been repaired and tested working? I'd love to compare it to mine to see if there are any issues with some solder points that perhaps should not be touching.There are a few that do and are likely supposed to, but I'm jut not sure. 

Here are some images of the PSU after doing my recap.

Underside:
http://retro-type.com/X68000/X68000-XVI-PSU-01.jpg
http://retro-type.com/X68000/X68000-XVI-PSU-02.jpg

Top:
http://retro-type.com/X68000/X68000-XVI-PSU-03.jpg
http://retro-type.com/X68000/X68000-XVI-PSU-04.jpg
http://retro-type.com/X68000/X68000-XVI-PSU-05.jpg

Parts I've ordered so far that could be some replacements for the middle area of the board (as well as some replacement voltage regulators / heat sinks) where I suspect the problem lies since everything is so clumped together and it's right after the fuse, and the largest cap on the board I wasn't seeing it holding a charge.

Transistor - C1815
http://www.taydaelectronics.com/t-transistors/2sc1815-c1815-transistor-npn-50v-0-15a.html

Voltage Regulator - Heat Sink? K643 2SK643
http://www.aliexpress.com/store/product/K643-2SK643/1955027_32628604598.html

Regulator / Transistor - 3122V
http://www.aliexpress.com/item/Free-shipping-5PCS-High-three-terminal-regulator-transistor-3122V/1857987515.html?spm=2114.40010508.4.32.iUZB8l

HZS7B-1 Zener Diode DCM-560
https://bestbuy.partsearch.com/Part/Denon%20Electronics/Denon/2760465909/New.aspx

Thank you all very much for reading. I'm hoping that I can eventually get this machine repaired. I'm a beginner when it comes to repairing electronics so any help would be appreciated!

-Thomas