Atari STE 4 Bombs - WD1772 replacement?

[rubber_jonnie]

There are diag carts in the store: Diag Cart

They are the standard Atari field service diagnostic images and are more than enough for most jobs.

Just oredered one, along with the cable and some caps for both my STE and Falcon PSUs. Figured it was about time I dealt with those lest I have more problems down the line. Will post back with what I find once the cart arrives.

Cool :)

[matt.lacey]

@rubber_jonnie So.. I got the cart.

Found two different errors while running tests, one was a bad CRC on the TOS ROM (1.62) and the other is DMA, which is probably what explains the four bombs. The floppy tests seem to actuallly work ok.

So I guess the next step is to check continuity between each of the DMA pins and whatever each should be connected to?

[exxos]

@matt.lacey The DMA test cannot be done (along with some other tests) without a additional test harness setup which unfortunately nobody manufacturers any more. So those DMA errors are actually as expected.

Also relating to the TOS checksum, it does not necessarily mean your ROM is faulty. It depends what ROM chips you have in your machine. Sometimes custom ROMs can have padding such as 00 or FF in them which can affect the checksum. It by no means has any detrimental effect to the system In that respect.

[matt.lacey]

@matt.lacey The DMA test cannot be done (along with some other tests) without a additional test harness setup which unfortunately nobody manufacturers any more. So those DMA errors are actually as expected.

Ah! Well that's good to know. I ran the floppy Disk Exerciser for quite some time and it didn't have any issues whatsoever, so not sure what to make of my 4 bombs on boot issue!

[exxos]

Ah! Well that's good to know. I ran the floppy Disk Exerciser for quite some time and it didn't have any issues whatsoever, so not sure what to make of my 4 bombs on boot issue!

Do you still get the bombs with no floppy in the drive ?

[matt.lacey]

Yep - same four bombs even if I remove the floppy or even the drive itself. There's no activity from the drive when the machine starts and no LED flash etc.

I was genuinely surprised when it started working perfectly fine when commanded by the diagnostic cart.

[exxos]

I was genuinely surprised when it started working perfectly fine when commanded by the diagnostic cart.

I have had odd things like that happen. Is normally down to a unstable bus or similar.

Can you post a image of your motherboard so we know which one you actually have...

[matt.lacey]

PXL_20230404_213333987.jpg

It was working fine last year, but then got shipped around the world and stored for a while. Might be time to start reflowing some joints. Have pushed down every chip that's socketed.

[exxos]

It was working fine last year, but then got shipped around the world and stored for a while. Might be time to start reflowing some joints. Have pushed down every chip that's socketed.

I think firstly you need to recap your power supply. While it is a little odd it works with the diagnostic cartridge you have to take tests with a pinch of salt sometimes.

For example, what generally happens is when TOS accesses the drive, it causes a current surge where bad regulation on the power supply causes the system to crash. However when running from a diagnostic cartridge things are just more stable because the operating system is not going anywhere near as much and is unlikely to be using RAM much, unlike running TOS.

Secondly I would remove CPU and blitter and like the contacts with some IPA. Sometimes if the blitter is malfunctioning TOS can crash during odd points during start-up. Sometimes crashing during floppy access can be a red herring.

Also check P100 Resistor pack (one on the right underneath the blitter) and see what value it is. If it is "222" (2.2K) then it is the incorrect one and needs to be changed for a 1.2K pack.

It is worth checking the other resistor packs as Atari's own fixes used 4.7K and 10K resistor packs around the CPU. I personally recommend those are changed to 2.2K anyway.

It is also possible you could have pull-up issues which require soldering a resistor pack on the DMA databus as outlined in the mandatory fixes. You can get all sorts of strange issues without those pull-up resistors.

It looks like you have the original Atari ROMs in there ? odd they are not in sockets though. When using the diagnostic cartridge you need to make sure you have the STE jumpers set. though I have never tried checksum tests on those ROM versions. Maybe someone else can verify if the checksum is valid on the cartridge or not with the same TOS versions on a STE ?

You also actually have parity Simms in there which can cause stable with the issues in some cases.

Overall you really need to work through all these things one by one as they are all known faults/issues with these machines.

[rubber_jonnie]

@rubber_jonnie So.. I got the cart.

Found two different errors while running tests, one was a bad CRC on the TOS ROM (1.62) and the other is DMA, which is probably what explains the four bombs. The floppy tests seem to actuallly work ok.

So I guess the next step is to check continuity between each of the DMA pins and whatever each should be connected to?

Theres a little more detail about the testing harness here: Diag cartridge test harness but basically you can't test the serial port, printer port, ACSI port, Joystick ports and Midi ports.

Although I do have a test harness, it doesn't test the enhanced 15 pin joystick ports as there is no harness for them, so they always error. As @exxos mentioned, the CRC checks for the ROMs often don't work as expected.

It's interesting that the FDD works fine with the diag cart, it sounds like the test in TOS that causes it to fail with 4 bombs is doing just that, failing, but the diag cart is ignoring it.

I think you do need to work through exxos suggestions and any other mandatory fixes.