exxos's Atari, Amiga & retro forum

atari030 wrote: 03 Sep 2020 00:40 Yeah mate, I installed pins and jumpers and socketed the 74LS11. It spat out bus errors randomly after that, I tried three sets of ROM's. Removing the IC was hard yakka, plenty of ground and solder on both layers.

I'm more disappointed in myself for not checking my mice first. :-) At least the KB now has a fresh flow of solder. :mrgreen:

Damn :(

Such is life. :D Patience and persistence. I have had these machines lying around for 20 years.

Cart and DMA chip arrive, just over a month. Pretty good considering Melbourne is in total lockdown.

MegaST2 with two chips gets a clean bill of health. Onwards.

Kaos six chip Mega2 fails, All checksum errors. Looks like a bad ROM burn. Six chip 1.04 passes but RAM errors all up the wazzoo. I guess an address problem.

MegaSTE is still white screen. I have to get hold of a USB to serial cable from work and check that out. The other Mega4 has to be faulty RAM. Desolder the lot and get a 4MB Exxoss set I reckon. I might have spare RAM lying around, though.

Hi atari030,
Dis you manage to fix your MSTE?
What was RAM chips the issue?

90% done mate, the main issue is bad joints and broken traces. Right now it looks like a DMA problem, it's suffering floppy and HDD issues.

I've recapped the board, replaced the CPU for an 16Mhz HC, replaced a ton of corroded resistors, repaired traces and reflowed bad joints and tweaked the CPU and blitter sockets.

I've put more in my top of the pile bloggy. Progress is slow but positive.

After a great deal of reading and faffing about the next job will be pull up resistors on the 1772 and a bus resistor swap. So, to recap on jobs done...... :lol:

Recapped the PSU and Mainboard.
Replaced coroded components.
Repaired broken traces and/or reflowed bad joints.
Blew up and repaired the composite output.
Swapped between parity and non parity RAM.
Swapped between modern 1.44 to Gotek.

All diag cart tests pass bar the floppy test. I have a spare 1772 so I will put some pullups on that to allow for easy change as the need arrises.
Given the severity of the DMA failures I was looking at the bus resistors. Has anyone done the bus resistors on a MegaSTE before?

atari030 wrote: 09 Jun 2022 22:42 . Has anyone done the bus resistors on a MegaSTE before?

I think @Steve might have done?. But the MSTE is kinda new territory in terms of fixes. I've not done any research into those machines at all. Kinda had enough after the never end faults on the STFM/STE :lol: :roll:

I've repaired a few Falcons and STFM's, The STFM's seemed pretty easy to work on, Falcon was a challenge but the bastard machine awards go to this MegaSTE, 130XE's and the other dodgy MEGST I have.

I haven't worked on the mega STe before, its DMA chip is the square type surface mount isn't it? I'd probably flux up the pads, then press my soldering iron to each leg just to reflow each connection. Then I'd perhaps put a 1uf ceramic or poly cap between gnd on the chip and a strong ground point elsewhere to try and reduce ground spikes.