exxos's Atari, Amiga & retro forum

That's a bloody good result. Well done.

atari030 wrote: 24 Dec 2020 01:55 That's a bloody good result. Well done.

Cheers :D

I had to chuck the whole lot at it, schematic tracing, logic probes, multimeters, scopes.

I was about to chuck the logic analyser at it too when I did one last run of the scope over the data lines and they just didn't match the good machine I had.

Just realised I need to sort out a PSU mount too, annoying as I have several spare ST PSUs, and I even have a working Mega PSU board, just not the metal tray.

Bugger. I've got a meanwell rd-65 I picked up while I was working at Jaycar last year. Its great but too big to fit in the Mega. The power connectors are the same between the ST and Mega. I just desoldered the AC side and badda bing. The Megafile frame is different again......

I guess I got lucky getting a PSU frame last year by the look of it.

atari030 wrote: 26 Dec 2020 21:41 Bugger. I've got a meanwell rd-65 I picked up while I was working at Jaycar last year. Its great but too big to fit in the Mega. The power connectors are the same between the ST and Mega. I just desoldered the AC side and badda bing. The Megafile frame is different again......

I guess I got lucky getting a PSU frame last year by the look of it.

Yeah, if you got a frame, you did get lucky. Might have a go at making a 3d printed one. Shame I don't have access to the metalwork shop from when I was in the RAF, as we made exactly that sort of thing. Asking around now to see if anybody has a spare, even dead, that they'd be willing to part with.

The RD-50A fits perfectly in the Mega BTW, which is how come I have a spare PCB, I just had the RD to hand and decided to swap it out. The RD65 is a LOT bigger, so definitely won't fit the standard Mega mounting plate like the RD50-A.


This is in my Mega 4, and what I'm using to test this Mega with.

I use RT-65B in two of my Megas. It's a tight fit though. It's the same size as RD-65.

Wow, that is tight. I'll look into that again, I think. Cheers DoG.

The frame I picked up was original Atari. Sold as working, clearly not but I got it cheap so oh well. Same type of failure as my other MegaST and an older FM. Of the three I have, all stuffed. Low voltage under load.

DoG wrote: 27 Dec 2020 00:10 I use RT-65B in two of my Megas. It's a tight fit though. It's the same size as RD-65.

That PSU is quite a snug fit!

Well, happily I've managed to secure the metal frame for a Mega ST PSU, so hopefully by the time I've finished sorting the RAM upgrade, cleaned and prepped the case and got everything else together such as screws etc, it'll hopefully be here and I can close everything up :)

So this one is definitely getting there.

Ok, so it seems there's more possible good news :)

The weird 3MB ram expansion is back in, and I get 4MB reported. I did try running YAART, but had managed to get literally hundreds of errors, until I re-read the instructions and realised the boot disk I was using had accessories and control panel on it, something that YAART doesn't like at all.

So a quick boot disk cleanup, leaving only SYSINFO, which is reporting 4MB RAM and YAART, which is now up to about pass 6 with no errors so far. I'll give it a good old long run just to be sure.

So it's looking like the RAM may be good now! That being the last thing to do other than clean up the case and fit the battery harness for the RTC.

Oddly the diag cart RAM test still fails, but I am wondering if that is something to do with the odd way this expansion is made. Since I have a different diag cart coming as part of my ST external test harness, we'll see what that reports when I try it.

TBH if the YAART testing comes back clean, I'm going to give it the thumbs up.

So far the fixes and mods it's had are:

1. Replacement DMA chip, as the defective original was preventing the floppy from working:
2. Updated TOS 1.04 which includes boot info and is patched for IDE.
3. FDD controller data bus pull-ups.
4. Replacement data bus pull-ups across the board.
5. Megabus IDE adapter and CF adapter with 4GB card.

Just waiting on the PSU frame now, as it's currently borrowing the PSU from my Mega 4, a rebuilt unit with Meanwell RD50-A. Once that arrives I can finish it off :)

Trouble is, all my STs bar one (It's stuck at my parents house and I can't visit them) are all in a good state of repair, so I'm having to find other projects like the ZX81 to keep my brain ticking over!

Got a Spectrum to fix next, and maybe one day I'll get back to the Mac Classic, though I'm worried it's a goner :(

So far so good 😁