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Recapped, didn't work, now works - huh?
Posted: 06 Jun 2024 20:27
by Hellraiseruk
OK, got my Mitsumi SR98 on the bench and installed the full exxos kit to recap it, resistors, caps and all. Powered it on, and got 3v on the 5v rail, and just under 7v on the 12v rail. Powered off, had a cuppa, then dismantled it to have a look. No signs of any issues, all solder joints fine, checked for shorts, no sign. Scrubbed the board with a toothbrush to make sure there were no random solder whiskers, reassembled and blow me down it now works fine. Any idea what would have caused the original issue? Can I really have been that lucky and just been the victim of an errant solder whisker?
Turned the volts down a bit, now have 4.98v on the 5v rail and 11.7 on the 12v which is fine by me :)
Re: Recapped, didn't work, now works - huh?
Posted: 07 Jun 2024 08:59
by rubber_jonnie
Hellraiseruk wrote: 06 Jun 2024 20:27
OK, got my Mitsumi SR98 on the bench and installed the full exxos kit to recap it, resistors, caps and all. Powered it on, and got 3v on the 5v rail, and just under 7v on the 12v rail. Powered off, had a cuppa, then dismantled it to have a look. No signs of any issues, all solder joints fine, checked for shorts, no sign. Scrubbed the board with a toothbrush to make sure there were no random solder whiskers, reassembled and blow me down it now works fine. Any idea what would have caused the original issue? Can I really have been that lucky and just been the victim of an errant solder whisker?
Turned the volts down a bit, now have 4.98v on the 5v rail and 11.7 on the 12v which is fine by me :)
Did you power it on with a load? If not you may get odd results as these always need a load to start properly.
Re: Recapped, didn't work, now works - huh?
Posted: 07 Jun 2024 10:25
by Hellraiseruk
Yep, hooked up to an ST :) Yes, I know, should have used load resistors but wasn't anticipating problems as I've recapped PSUs before. Solid as a rock now though, so looks like it was a bit of a solder whisker.
Thinking about it, if you disconnected the PSU from the mainboard but left the floppy connected (just power, not data) would that be sufficient load?
Might invest in one of those desoldering guns, problem with the old fashioned manual desoldering pump is that when it fires it sends fragments of solder in all directions no matter how frequently you clean it, and it looks like one of those might well have taken up residence for a brief period. However, all is now fine, PSU is working like a charm. Next is to find out why my monitor output still doesn't work, yet is fine over RF, that's a job for the weekend :)
Re: Recapped, didn't work, now works - huh?
Posted: 07 Jun 2024 10:36
by rubber_jonnie
Hellraiseruk wrote: 07 Jun 2024 10:25
Yep, hooked up to an ST :) Yes, I know, should have used load resistors but wasn't anticipating problems as I've recapped PSUs before. Solid as a rock now though, so looks like it was a bit of a solder whisker.
Thinking about it, if you disconnected the PSU from the mainboard but left the floppy connected (just power, not data) would that be sufficient load?
Might invest in one of those desoldering guns, problem with the old fashioned manual desoldering pump is that when it fires it sends fragments of solder in all directions no matter how frequently you clean it, and it looks like one of those might well have taken up residence for a brief period. However, all is now fine, PSU is working like a charm. Next is to find out why my monitor output still doesn't work, yet is fine over RF, that's a job for the weekend :)
Good stuff :)
I can recommend a desoldering gun, they are such a timesaver, but you do have to be careful, it's all too easy to apply too much pressure to whatever your desoldering and damage vias and traces, I know I've done it.
As long as you take your time and keep it just touching it works just fine.
I have seen videos lately extolling the virtues of the Hakko desoldering gun, but they are so expensive, 4x the cost of my Duratool and for me, as I'm not running a repair shop or YouTube channel, I'll take the Duratool.
Whilst the Hakko does have some nice features, but I like that the gun for the Duratool is lighter and that if it fails, the guns are cheap to buy a replacement for. I had to replace mine and it was just £23.
Re: Recapped, didn't work, now works - huh?
Posted: 07 Jun 2024 10:36
by Steve
No a floppy wouldn't be sufficient. Plus you need to load both the 5v and 12v continuously, with load resistors. Gotta be careful with these old PSUs, not only will you get a bad reading but you can also damage them by running them without a load.
Re: Recapped, didn't work, now works - huh?
Posted: 07 Jun 2024 11:24
by rubber_jonnie
Steve wrote: 07 Jun 2024 10:36
No a floppy wouldn't be sufficient. Plus you need to load both the 5v and 12v continuously, with load resistors. Gotta be careful with these old PSUs, not only will you get a bad reading but you can also damage them by running them without a load.
I have to agree with Steve here, there is very little load on a floppy unless it's actually running and certainly not enough to load up the PSU to a point where it would work properly.
Re: Recapped, didn't work, now works - huh?
Posted: 07 Jun 2024 12:15
by Hellraiseruk
Fair enough, just seemed like a potential quick and dirty option if no big resistors to hand, but not to worry.
Yes, I've looked at the duratool and will probably go that way for the reasons you mentioned - quarter of the price of the Hakko, and cheap enough to replace the gun if it breaks. From what I've read you have to be religious about keeping the gun clean so the solder doesn't set within the gun and block it, any fixes to prevent that happening that you know of?
Cheers
Re: Recapped, didn't work, now works - huh?
Posted: 07 Jun 2024 13:19
by rubber_jonnie
Hellraiseruk wrote: 07 Jun 2024 12:15
Fair enough, just seemed like a potential quick and dirty option if no big resistors to hand, but not to worry.
Yes, I've looked at the duratool and will probably go that way for the reasons you mentioned - quarter of the price of the Hakko, and cheap enough to replace the gun if it breaks. From what I've read you have to be religious about keeping the gun clean so the solder doesn't set within the gun and block it, any fixes to prevent that happening that you know of?
Cheers
I clean mine during use and give it a squeeze of the trigger before I finish with it.
My original gun blocked and after clearing it, it never worked properly again. The new gun seems a lot better and tends not to block.
Re: Recapped, didn't work, now works - huh?
Posted: 07 Jun 2024 13:35
by Hellraiseruk
Cheers, bit too late to drop hints for Father's day, so might have to make a purchase :)