Diagnosing an 800XL Black Screen

[RetroStevo]

He everyone.

 

I'm looking for some guidance please.

I was extremely kindly gifted an 800Xl by an old friend which booted to a black screen.

 

I have some electronics experience but an certainly not a 8-bit expert, I did some research and found the DL Chip was the most lightly cause. After sourcing one, I did some tests with my old logic tester (should have done this first) and found all inputs and outputs of the DL seemed healthy. I decided to power through and remove the original DL Chip & insert a socket instead. After socketing the DL Chip, the original and recently sourced DL chips do exactly the same and both have seemingly healthy ins and outs.

 

CLK all seems fine, VCC & VSS all seem OK.

 

Ive just spent the last 3 hours checking signals with the Logic probe (I know, i should have broke out my trust old oscilloscope to be sure) but everything (according to the 800 XL service manual seems to be as it should be......EXCEPT.............. I have some seemingly strange results on the ANTIC chip. I could be a gazillion miles away from the faulty, but why do I se no activity on all of the LUMA pins?

 

Ive attached a couple of pics, 1 that shows what I beleive to be all the IC's and the other is the state of the ANTIC.

 

And help/advice would be very much appreciated.

 

Thanks in advance.

 

 

 

 

Edited May 27 by RetroStevo
Wrong Photo

[flashjazzcat]

The OS probably crashed before setting up a display list (perhaps explaining the lack of LUMA), and since Micron DRAMs are soldered to the board, they're a plausible cause of issues.

[Dopeyman06]

Remove and replace those RAM chips. Those MT chips are known to fail. I’m not saying that that’s the cause of your issues, but those chips definitely fail. 
 

[RetroStevo]

Thank for your UNBELEIVABLY quick reply - I realised that my listing of the signals was wrong (REMEMBER CLOCKWISE STEVO!!!) - I had tested the pins correctly but written then down wrong. I'll pop you a DM Mr FJC and maybe you could help me source a new OS Chip???

[flashjazzcat]

I have plenty of OS ROM chips; you're welcome to one, although I fancy it's the RAM.

 

[RetroStevo]

Thanks FJC - What's the best way to get directly in touch with you? I cant seem to Dm you???????

[TZJB]

56 minutes ago, RetroStevo said:

He everyone.

 

I'm looking for some guidance please.

I was extremely kindly gifted an 800Xl by an old friend which booted to a black screen.

 

I have some electronics experience but an certainly not a 8-bit expert, I did some research and found the DL Chip was the most lightly cause. After sourcing one, I did some tests with my old logic tester (should have done this first) and found all inputs and outputs of the DL seemed healthy. I decided to power through and remove the original DL Chip & insert a socket instead. After socketing the DL Chip, the original and recently sourced DL chips do exactly the same and both have seemingly healthy ins and outs.

 

CLK all seems fine, VCC & VSS all seem OK.

 

Ive just spent the last 3 hours checking signals with the Logic probe (I know, i should have broke out my trust old oscilloscope to be sure) but everything (according to the 800 XL service manual seems to be as it should be......EXCEPT.............. I have some seemingly strange results on the ANTIC chip. I could be a gazillion miles away from the faulty, but why do I se no activity on all of the LUMA pins?

 

Ive attached a couple of pics, 1 that shows what I beleive to be all the IC's and the other is the state of the ANTIC.

 

And help/advice would be very much appreciated.

 

Thanks in advance.

 

 

 

 

 

Normally there should be activity on all Address and Data Bus lines. As the Buses are shared between several chips it will be hard to determine which one is at fault without substitution.

 

However replacing the DRAM chips is the first priority and advisable due to the high Micron Technology 4264 memory failure rate and it may solve the problem.

 

I also always advise that, to save a further purchase later, the 4164/4264 DRAM memory chips are replaced with 41256 DRAM memory which may allow you to expand the standard 64KB memory at a later date.

 

By default they will use only the 64Kb portion of each chip as pin 1 is held high, but by adding an additional memory decoder and wiring at a later date, this can be expanded to the full 256KB of all eight DRAM chips.

 

Incidentally your existing OS ROM has a high probability of being fine. What type of OS ROM are you looking for? As well as official Atari operating systems there are many others and they can be programmed into EPROMs quite easily.

[RetroStevo]

18 hours ago, TZJB said:

 

Normally there should be activity on all Address and Data Bus lines. As the Buses are shared between several chips it will be hard to determine which one is at fault without substitution.

 

However replacing the DRAM chips is the first priority and advisable due to the high Micron Technology 4264 memory failure rate and it may solve the problem.

 

I also always advise that, to save a further purchase later, the 4164/4264 DRAM memory chips are replaced with 41256 DRAM memory which may allow you to expand the standard 64KB memory at a later date.

 

By default they will use only the 64Kb portion of each chip as pin 1 is held high, but by adding an additional memory decoder and wiring at a later date, this can be expanded to the full 256KB of all eight DRAM chips.

 

Incidentally your existing OS ROM has a high probability of being fine. What type of OS ROM are you looking for? As well as official Atari operating systems there are many others and they can be programmed into EPROMs quite easily.

Thanks for the info - I want to keep this machine as original as possible so If I do replace the OS I would want one as similar as possible to the one that's currently installed. I am going with everyone's advice and will be replacing the RAM chips first and then take it from there if that doesn't resolve the issue. If you had a link and/or recommendation for a set of 41256 DRAM chips I would be very grateful. Thanks again!

[TZJB]

26 minutes ago, RetroStevo said:

Thanks for the info - I want to keep this machine as original as possible so If I do replace the OS I would want one as similar as possible to the one that's currently installed. I am going with everyone's advice and will be replacing the RAM chips first and then take it from there if that doesn't resolve the issue. If you had a link and/or recommendation for a set of 41256 DRAM chips I would be very grateful. Thanks again!

 

You say that now, but the better option for the XL OS is the XL/XE Rev 3. They are normally Rev. 2. Here if you decide to roll your own.

 

 

 

 

I cannot recommend any supplier, and I don't know where you are in the world, but after a quick search on eBay UK came up with two options from the same supplier:-

 

https://www.ebay.co.uk/itm/273186512925 LOT OF 10pcs OKI M41256A-10 Dynamic RAM Page Mode 256K x 1 16-Pin DIP £17.95

 

OKI MSM41256A.PDF

 

https://www.ebay.co.uk/itm/273100954587 LOT OF 25pcs Hitachi HM51256LP-15 CMOS Dynamic RAM 16-Pin DIP £14.20

 

HITACHI HM51256.pdf

 

They seem to be essentially the same for our purposes and the cheaper lot has enough for three 800XL!

 

See what you think.

 

 

[RetroStevo]

36 minutes ago, TZJB said:

 

You say that now, but the better option for the XL OS is the XL/XE Rev 3. They are normally Rev. 2. Here if you decide to roll your own.

 

 

 

 

I cannot recommend any supplier, and I don't know where you are in the world, but after a quick search on eBay UK came up with two options from the same supplier:-

 

https://www.ebay.co.uk/itm/273186512925 LOT OF 10pcs OKI M41256A-10 Dynamic RAM Page Mode 256K x 1 16-Pin DIP £17.95

 

OKI MSM41256A.PDF 708.15 kB · 0 downloads

 

https://www.ebay.co.uk/itm/273100954587 LOT OF 25pcs Hitachi HM51256LP-15 CMOS Dynamic RAM 16-Pin DIP £14.20

 

HITACHI HM51256.pdf 264.84 kB · 1 download

 

They seem to be essentially the same for our purposes and the cheaper lot has enough for three 800XL!

 

See what you think.

 

 

Thanks for the info - That's a great help! Cheers!