exxos's Atari, Amiga & retro forum

Well, I am still seeing some oddities I don't like and they are mostly present when the PSU is warm, so I've made the executive decision to recap the PSU. Unusually, I do actually have some of the replacements already, hopefully the rest will arrive this week and I can get it back together sharpish.

PSU is apart, and is looking reasonable if I'm honest, but you just can't see inside those caps. The oldest IC I can see is from 1983, so it is 40 years old when all said and done and deserves a service.

I replaced the caps I had in stock this morning and tested the old items.

The 10v1000uF caps all tested out of circuit are reading about 1800-1900uF. I'd expect maybe a 20% tolerance, but that is well beyond that, so in go the new ones.

The 10v220uF caps tested between 265-275uF which is at the top end of a 20% tolerance, so just about in. It'll be interesting to see what the others read when I pull them out.

Have also now ordered the v2 Analog PCBs from JLPCB, so now need to get the BoM and order the parts. There'll be 5 in total so I may have spares later if anybody is interested, they are VGA boards for the Apple ][.

Some very fine soldering involved though, I hope I'm up to it!!

More replacement caps arrived today, and a quick test showed that everything so far removed from the PSU are between 60&90% off their marked values.

They have a specified tolerance of +-55% and only a couple out of the 10 caps I've removed so far have been close to that, and they were 60% over. These are all on the low voltage side of the PSU.

On the mains side, all 4 of the caps are within 10% of their advertised values, which is excellent, however they are all 85C parts and I will replace with 105C parts because I have them and also because of their age.

New ones going in are Nichicon, Panasonic and Rubycons.

Ok, so PSU has now had a full cap replacement and so begins the testing. I have also replaced the TCA 650 IC as I feel the old one may be marginal.

So far, things are running fine, the 80column/RAM card has not disappeared and video is rather more crisp than it was, and 80 column mode in particular seems to be much sharper.

Fingers crossed all is now well :)

Well, the finger crossing didn't help as the 80 column/RAM card is still playing up.

The machine otherwise passes all the other diagnostics I can throw at it, so it looks like the RAM2E II has got a fault, so I will contact the seller via Tindie where I ordered it and see if they can advise.

I may do a very quick reflow since there aren't many components on it, see if that helps.

Well, the post reflow results are in, and the card is still failing with memory corruption after about 5 or 10 minutes, causing the card to vanish and no longer detected.

Damn it.

I've managed to get a cheap 80 column/64K modern remake of the original Apple expansion card which is tested and working and I aim to use it to test the expansion socket.

Before anybody shouts out 'Clean the card contacts and socket', that's already been done, including a spray with Electrolube EML, and it made no difference.

I'll have a look at the RAM chip on the RAM2E II card, see if I can get a replacement, but I hope it isn't the CPLD that's faulty. Could also be the level shifters, but I don't want to rebuild the whole card!!!

CPLD? So, this is a newish card?

Tried some freeze spray on the chips to try to see which one is failing/recovering?

stephen_usher wrote: 02 Apr 2023 13:32 CPLD? So, this is a newish card?

Tried some freeze spray on the chips to try to see which one is failing/recovering?

It is new, yes. I keep meaning to get some freeze but don't have any as yet, though I did put a fan on it yesterday and no difference.

Unfortunately once it goes it locks up, so it won't recover. However if I leave it 5 minutes it does usually recover, so I may be able to make it recover quicker.

Alternative freeze spray: Dust blower aerosol held upside-down.