Atari STE 4 Bombs - WD1772 replacement?

[exxos]

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.

It is odd. Though if the PSU is bad, it might just work during diagnostics and fail with the load of the full OS running. But that should be serviced first. Otherwise you can end up chasing faults which are not really there.

I forget at what point TOS enables the blitter. But if the blitter is bad, or it has bus grant issues ( bad connection or P100 wrong value ) it would bomb somewhere on startup.

TOS206 is probably better as I don't think earlier versions do memory test etc ?

[matt.lacey]

Ugh - didn't mean to go radio silent last night, actually wrote the following but never hit submit!

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I appreciate all the info - that's a good list to work through. As you know I got some caps for the PSU with the diagnostic cart, so will start there. Should have time to do that tomorrow. Don't think I've got a PLCC puller around so will get one of those to reseat the CPU and blitter.

Dumb question: how do you measure resistor packs? Done normal resistors before but not these. Assume it's between the GND PIN and each of the others? If that's the case then on P100 I read 1.2K. Between any two consecutive pins that aren't GND I get 2.4, so I assume that's because I'm reading two idependant resistors in series?

They are the original ROM chips, and yep, they're soldered.

[exxos]

Dumb question: how do you measure resistor packs? Done normal resistors before but not these. Assume it's between the GND PIN and each of the others? If that's the case then on P100 I read 1.2K. Between any two consecutive pins that aren't GND I get 2.4, so I assume that's because I'm reading two idependant resistors in series?

You don't need to measure them really. Just look at the numbers on them.

Pin 1 is normally marked as a dot on the package and normally a square pad on the PCB. It is connected to 5v. Then internally the top end of a row of resistors is also connected to pin 1. The other 8 pins are the other ends of the resistors.

Though you may get bad readings trying to measure them in circuit. So just easier to look for the numbers printed on them.

EG.
122 = 1.2k ( 1 2 00)
222 = 2.2k ( 2 2 00)
472 = 4.7k ( 4 7 00)
103 = 10k ( 1 0 000)

The first 2 numbers are the value and the 3rd is the number is zeros.

It sounds like you have 1.2k for p100 . So that is good news. There should be 103 and 472 around the CPU.

EDIT:

cb.jpg

[matt.lacey]

Hah - I'd not seen the text (thought it was odd they were unlabelled) because it's on the flip side and bloody faint. But now I know how they're made I know I was measuring them correctly.

101, 102 & 103 are both 4.7K

104 I read as ~5.5K - used the meter for that because can't see the text at all due it it's proximity to the CPU. Will spend my lunch time doing the caps on the PSU.

[matt.lacey]

So any tips for dealing with the glue on these things? Swapped out the 250V by the regulator and did the regulator itself, but the other 250V cap is fixed in with so much crap that's really awkward to get to. Noticed on the other one it melted a bit while I was removing solder from the other side, so hair dryer?

[BigSteve]

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 ?

STe Factory ROMs TOS v1.62 (C301165-002A/C301166-002A) with STe Diags cart v1.9 gives:

ste-1-62-romdiags.jpg

[rubber_jonnie]

So any tips for dealing with the glue on these things? Swapped out the 250V by the regulator and did the regulator itself, but the other 250V cap is fixed in with so much crap that's really awkward to get to. Noticed on the other one it melted a bit while I was removing solder from the other side, so hair dryer?

I usually find it's so dry it'll pry away easily, but a hairdryer may soften it, but in my case I use my hot air wand.

If you have any IPA you can try scooshing some around the stuck areas whilst prying.

Alternatively you may need to carefully cut with snips.

[matt.lacey]

PXL_20230405_151641032.jpg

[matt.lacey]

Based on this I'm guessing my low ROM chip has either died or has a bad connection somewhere. Will reflow it tonight and see where that gets me. Got the PSU caps sorted out - dug away at the glue with a screwdriver on the tricky one and eventually got it.

[exxos]

Based on this I'm guessing my low ROM chip has either died or has a bad connection somewhere. Will reflow it tonight and see where that gets me. Got the PSU caps sorted out - dug away at the glue with a screwdriver on the tricky one and eventually got it.

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.