exxos's Atari, Amiga & retro forum

This is the MMU I am talking about.

I know early machines were somewhat different .. and later machines did the GST MMU - - I have a

https://www.exxosforum.co.uk/forum/viewt ... f=55&t=797 C100501-001 rev1..

I have 4 other megaST here.. most rev5 100167.. but can I just take an mmu from them.. and try it in the above see if it gets me past this T4 error?

James

I can't make out the RAM numbers on that image.

All the MMU's the ST/F/M/MEGA ST are the same.

I can confirm as exxos says, the MMU is interchangeable with that board.

Other suggestions for the T4 error would be ram fault or the 74LS373 and 244s have a problem.

I've also experienced a lot of ram faults with the Megas I've had. One one I fitted exxos's 4mb upgrade and binned the original memory. On another I binned all the old ram and put 1 bank with soj13 adaptors? With 4mb on it and rewired the high bit of the ram.

Ok, so suggestion?

sub the mmu first?

Since I cannot get past the timing issue to test ram.. how do I move to the next item?

Suggestions on troubleshooting?

James

Remove and reseat the glue and MMU, making sure that all the pins in both sockets are clean and make good contact.

Also do the same with the shifter if its sockets.

Shifter turns 32mhz into 16mhz.
Glue sends out 4 and 8mhz clocks.
Then there's the 512khz and 1mhz clocks. Cant remember where from.

Be good to check those all out with a scope.

unfortunately no scope.

I have a friend I might be able to get to check if the re-seat does not work.. by scope you mean just confirming they are putting out what they are supposed to in cycles?

James

Bikerbob wrote: 15 Nov 2019 20:38 unfortunately no scope.

I have a friend I might be able to get to check if the re-seat does not work.. by scope you mean just confirming they are putting out what they are supposed to in cycles?

James

Yes for starters and the scope would also be useful for checking the activity on the ram chips, glue, mmu, etc.

So PhilC I have not tried subing all the chips.. just pulled checked and reseated.

Still same issue red screen T4 error. I have a plcc puller but these chips are not friendly.. anyone know a good puller for these Atari early plcc chips?

I could swap out chips one at a time with a known good computer.. I have attached a picture of the memory area.

Bikerbob wrote: 16 Nov 2019 04:41 I have a plcc puller but these chips are not friendly.. anyone know a good puller for these Atari early plcc chips?

I got mine out by buying a PLCC puller and then filing the ends down a bit to make them thin enough to get under the edges. Once you can get the fingers in underneath them they seem to come out OK!

Smonson wrote: 16 Nov 2019 07:21

Bikerbob wrote: 16 Nov 2019 04:41 I have a plcc puller but these chips are not friendly.. anyone know a good puller for these Atari early plcc chips?

I got mine out by buying a PLCC puller and then filing the ends down a bit to make them thin enough to get under the edges. Once you can get the fingers in underneath them they seem to come out OK!

These (ATARI) are the only machines I am playing with.. can you show me a pic of what you did? I would really prefer to stop scraping the chip each time the puller slips off.... grrrr

James