Atari STE 4 Bombs - WD1772 replacement?

[matt.lacey]

Yes looks like something is amiss with the rom . Thanks @BigSteve for posting the checksums.

I'd be surprised is the rom was bad. So let's hope a resolder can do the trick.

Yes, thank you @BigSteve! I suspect it might well be the ROM chip itself. I've reflowed and it made no difference, so then I checked for continuity. I knew power was good already but double checked GND and VCC, then checked all the address lines for continuity with the HI ROM chip, as well as the various signal lines. Then I checked the 8 data lines for continuity to the DMA chip. I guess next I'll check for continuity to the CPU for good measure.

Wouldn't be the worst excuse to get a dual TOS upgrade, but then I'd also hate to spend the cash on that if it's something else.

[matt.lacey]

@exxos my search-foo is failing me today - do you know where I can find the pin out for these 28 pin ROM chips? I was working off a 32 pin schematic last night but the address and data lines matched up which makes sense given 32 pin chips can go in the same positions. Found a page on the AF wiki that suggests the actual chip type isn't known?

Just curious because I've got some 28 pin eeproms from another project along with a way to write them, they're AT28C256 chips.

Ignore me. I clearly need more coffee this morning.

[matt.lacey]

Well that was a stressful evening. Got a cheap hot air rework station to help me get the ROM chips off, worked a treat. Couldn't clear the solder put of the power holes for the life of me, that trace was sinking too much heat.

PXL_20230414_195221506.jpg

Eventually pushed a socket in by melting that solder, though I only had 28 pin sockets to hand so used two of those and chopped two more for the extra four pins in each ROM location.

PXL_20230414_220413388.jpg

Got the 2.06 chips in, reassembled, put in the diagnostic cart and preyed to the silicon gods as I flicked the switch. Diagnostic cart booted, but the menu came up yellow. Flicks to blue momentarily when I toggle 50/60Hz, but then goes yellow again...not sure what that's about. Anyway, ran the ROM test and got a failure again.

PXL_20230414_225300128.jpg

Had a quick search but couldn't find the numbers to check against online. With a sinking heart I powered off, pulled the cart and started the machine. Got the Atari logo and RAM test, but then it froze with an odd black bar:

PXL_20230414_223730069.MP.jpg

Not sure if that's expected? Clearly shouldn't freeze but I'm unsure about the bar. After that I hit the reset switch and it fired up the Gem desktop. Need to do some more testing over the weekend but formatting a floppy and saving newdesk.inf worked fine!

@exxos any commentary would be appreciated!

[exxos]

The black bar is expected. It's just a delay which Atari added to give hard drives chance to spin up. You just press space-bar at any point after the memory test starts to skip it all.

[matt.lacey]

Ah OK, cool. Any idea on the crc failure? Could it just be padding? Would be good to build up a table of the correct values somewhere, and even if the "incorrect" (according to the diagnostic cart) ones that are known to be good for a given chip size and image

[rubber_jonnie]

Well that was a stressful evening. Got a cheap hot air rework station to help me get the ROM chips off, worked a treat. Couldn't clear the solder put of the power holes for the life of me, that trace was sinking too much heat.

A word of warning here, these boards are very easy to burn with hot air, so be really very careful when using it as the last thing you want to do is 'popcorn' the board, which is where the layers separate.

Whilst hot air can be useful in small doses to warm the board to help remove reluctant ICs, I'd recommend a de-solder gun or de-solder wick.

Good to see it's working :)

[Steve]

@matt.lacey I could be remembering wrong but as far as I remember the TOS CRC check will always fail as it's designed for a certain type of TOS only... Perhaps others can confirm?

[matt.lacey]

@matt.lacey I could be remembering wrong but as far as I remember the TOS CRC check will always fail as it's designed for a certain type of TOS only... Perhaps others can confirm?

My HI chip was seemingly correct for the old ROMS though I guess they were originals. Any idea what the yellow menu is caused by? Made it bloody hard to read! The colour test looked good so it's not a video issue

[Steve]

@matt.lacey honestly you don't need to worry about half that stuff. If the machine boots up and runs gembench & doesn't crash you're fine. Maybe run the YAART memory test to just make sure the ram is good too.

[rubber_jonnie]

@matt.lacey honestly you don't need to worry about half that stuff. If the machine boots up and runs gembench & doesn't crash you're fine. Maybe run the YAART memory test to just make sure the ram is good too.

@matt.lacey What Steve said...