800XL with black screen but more importantly a constant audio tone - any clues?

[Beeblebrox]

I've acquired a stock PAL 800XL. Powers up to a black screen so I am going to go through the usual as fixed a fair few now so know the drill. (Likely RAM/CPU as initial candidates.)

 

Normally I'd not need post up a topic for help for a black screen issue if it wasn't for the fact that in addition to the black screen there is something I've never come across before  - it's accompanied by constant loud audio tone soon as you power on.

 

I know there are likely a few issues contrubuting to the system not working properly here but does anyone have a clue as what might cause a loud constant audio tone?

 

FYI it's not the cable or my setup as works fine with other 800XLs, etc. I've checked the PCB's monitor jack also. Nothing under the board - look standard factory soldering, no additional components or jumper wires/DIY mods under there. No shorts.

 

My initial thoughts:

 

Aside the possible bad ram and/or PCU causing the black screen, for the audio tone perhaps a bad POKEY and/or some passive componentry failure?

 

The board:

 

Edited April 23, 2023 by Beeblebrox

[TZJB]

3 hours ago, Beeblebrox said:

I've acquired a stock PAL 800XL. Powers up to a black screen so I am going to go through the usual as fixed a fair few now so know the drill. (Likely RAM/CPU as initial candidates.)

 

Normally I'd not need post up a topic for help for a black screen issue if it wasn't for the fact that in addition to the black screen there is something I've never come across before  - it's accompanied by constant loud audio tone soon as you power on.

 

I know there are likely a few issues contrubuting to the system not working properly here but does anyone have a clue as what might cause a loud constant audio tone?

 

FYI it's not the cable or my setup as works fine with other 800XLs, etc. I've checked the PCB's monitor jack also. Nothing under the board - look standard factory soldering, no additional components or jumper wires/DIY mods under there. No shorts.

 

My initial thoughts:

 

Aside the possible bad ram and/or PCU causing the black screen, for the audio tone perhaps a bad POKEY and/or some passive componentry failure?

 

The board:

 

 

DRAM and CPU is my guess. Some MT DRAM has already been worked on but change out for tested 4164 or 41256 DRAM. You also have a Mexico CPU so it's 50/50 odds that it still works due to degradation. The POKEY is probably getting junk data input so test that last if the previous don't work out. The main problem that I have found is that there are so many IC's sharing the Data Bus, any of them could theoretically be affecting POKEY. I expect that you have a diagram, but this one attached is quite clear.

 

[+x=usr(1536)]

4 hours ago, Beeblebrox said:

Aside the possible bad ram and/or PCU causing the black screen, for the audio tone perhaps a bad POKEY and/or some passive componentry failure?

 

Just on the off chance...  Does the tone sound POKEY- or GTIA-generated?

[Beeblebrox]

31 minutes ago, x=usr(1536) said:

Just on the off chance...  Does the tone sound POKEY- or GTIA-generated?

not entirely sure but I'd say Pokey

 

BTW just tested the CPU in another A8 and it's fine. Swapped in another working CPU - same black screen and tone.

Edited April 23, 2023 by Beeblebrox

[+x=usr(1536)]

RAM would be my next stop.  Also swap the GTIA just for giggles if you happen to have one handy.  Don't think it's necessarily the problem, but with the board being socketed it's a quick test.

 

Other than that, passives and the usual MMU / delay line suspects, perhaps.  Good luck 

[+kheller2]

Always swap the "bad" parts into a working system to verify them.

Swapping good parts into a "bad" system could damage the part -- but eventually you might wind up there anyway.

 

The personality chips look socketed so you should be good to swap.   Except PIA RAM/ROM/BASIC.

[flashjazzcat]

That's Micron RAM and it looks like someone replaced two of the DRAMs already (in sockets), so it's entirely possible another one has died.

 

I see @TZJB already remarked on this.

 

 

Edited April 23, 2023 by flashjazzcat

[xrbrevin]

- socketed only 2x and put MT chips back in!

oddball behaviour.. 🤨

[Beeblebrox]

1 hour ago, xrbrevin said:

- socketed only 2x and put MT chips back in!

oddball behaviour.. 🤨

Yeah, strange. Maybe a previous owner only had two sockets and MT ram chips available at the time. I would always replace all with sockets and install non MT branded ram of course.

 

Anyways, good news - all sorted.

 

I didn't have any spare ram sockets but I did have a spare 64k Sram module.

 

So I removed all the ram chips, and installed that. (I also removed the Delay line chip as I know the Sram module replaces the Delay line functionality among other things and wasn't 100% sure what would happen if I left the old chip in. Removed it as a precaution).

 

Powered up with no issues.

 

So either it was just ram or both ram and delay line issues. As I say normally I'd figure a black screen non booting A8 out on my own these days, but the main reason for posting this topic was I'd never heard the audio tone issue. Seems it was caused by either bad ram, or a possible bad delay line.

 

Hooked up Chroma for colour on S-video and also lifted C54 (installed switch), to remove composite interferance on my LCD (using S-video all the time so this is standard practice for me for my LCD).

  

 

The original Mexico CPU works when re-installed BTW. (Did so after the photo was taken). Will keep it as a spare given they are unrealiable.

 

Only thing I need to double check is the socket profile for the CPU now the Sdram module is in place. (Original socket, Sdram module plus CPU). May well be the case won't close.

 

TBH I think I might just replenish my ram sockets stash and install some non MT ram chips I have lying around to save using the Sram module. (I've got a spare Delay line chip I can install if I do).

 

That's another evening.

 

Thanks for all the replies and suggestions.

 

 

Edited April 23, 2023 by Beeblebrox

[xrbrevin]

nicely resurrected!

 

[TZJB]

20 hours ago, Beeblebrox said:

Yeah, strange. Maybe a previous owner only had two sockets and MT ram chips available at the time. I would always replace all with sockets and install non MT branded ram of course.

 

Anyways, good news - all sorted.

 

I didn't have any spare ram sockets but I did have a spare 64k Sram module.

 

So I removed all the ram chips, and installed that. (I also removed the Delay line chip as I know the Sram module replaces the Delay line functionality among other things and wasn't 100% sure what would happen if I left the old chip in. Removed it as a precaution).

 

Powered up with no issues.

 

So either it was just ram or both ram and delay line issues. As I say normally I'd figure a black screen non booting A8 out on my own these days, but the main reason for posting this topic was I'd never heard the audio tone issue. Seems it was caused by either bad ram, or a possible bad delay line.

 

Hooked up Chroma for colour on S-video and also lifted C54 (installed switch), to remove composite interferance on my LCD (using S-video all the time so this is standard practice for me for my LCD).

  

 

The original Mexico CPU works when re-installed BTW. (Did so after the photo was taken). Will keep it as a spare given they are unrealiable.

 

Only thing I need to double check is the socket profile for the CPU now the Sdram module is in place. (Original socket, Sdram module plus CPU). May well be the case won't close.

 

TBH I think I might just replenish my ram sockets stash and install some non MT ram chips I have lying around to save using the Sram module. (I've got a spare Delay line chip I can install if I do).

 

That's another evening.

 

Thanks for all the replies and suggestions.

 

 

 

I am pleased for you that it's not a faulty CPU or POKEY and is probably just the DRAM that needs replacing.

 

Although the CPU is raised from the motherboard considerably with the 64K SRAM installed, it probably clears the keyboard so long as there is no top shield.

 

I have a TFHH 512K SRAM upgrade installed in a 800XL which is similar but sits in the GTIA socket and just clears the keyboard when assembled, again without the top shield which would otherwise need a window installed over the chip!

 

In my opinion, if the Mexico CPU still works you may as well use it, then you know it's still working and not rotting in a box.

 

When you get the time please do install the DRAM and let us see it working. Plus I believe you have a spare RamboXL board to use up, from the 800XLF? 😉

 

 

[Beeblebrox]

13 minutes ago, TZJB said:

 

I am pleased for you that it's not a faulty CPU or POKEY and is probably just the DRAM that needs replacing.

 

Although the CPU is raised from the motherboard considerably with the 64K SRAM installed, it probably clears the keyboard so long as there is no top shield.

 

I have a TFHH 512K SRAM upgrade installed in a 800XL which is similar but sits in the GTIA socket and just clears the keyboard when assembled, again without the top shield which would otherwise need a window installed over the chip!

 

In my opinion, if the Mexico CPU still works you may as well use it, then you know it's still working and not rotting in a box.

 

When you get the time please do install the DRAM and let us see it working. Plus I believe you have a spare RamboXL board to use up, from the 800XLF? 😉

 

 

Yup, will be installing the Drams and a delay line  - 16 pin sockets on order - since the casing definietly doesn't close with the Sram module currently in place. The original PCB single wipe soket, the Sram module and CPU all stacked is just that little bit too high. Needs 4mm more clearance. (I have analso keyboard in there which actually usually givens more clearance than the metal plate style XL keyboards.

 

Heh heh - you are also right re the Rambo XL - may well upgrade to 256k. Kinda had that board marked for another 800XL (latter will likely have TK-II stereo and UGV also).

 

I'll post images when done.  the drams/delay line/old Mexico CPU are in on this 800XL

Edited April 24, 2023 by Beeblebrox

[_The Doctor__]

check the older work vigorously as it might have worked or not worked when done, so check solder and sockets. Magnifying glass and meters are always a must.

[Beeblebrox]

8 minutes ago, _The Doctor__ said:

check the older work vigorously as it might have worked or not worked when done, so check solder and sockets. Magnifying glass and meters are always a must.

Yup. Glad it works in it's current fixed state.

 

I will do all that as part of the new dram sockets install. This will be the 3rd stock 800XL I've have successfully socketed ram for this past couple of months, and a good few A8s last year ...and whilst not a pro I am pretty handy with a soldering iron these days.

 

I always clean the board area once the original ram chips have been removed and vias cleared of solder, then I check the traces and vias and also I take pics. I also do continuity tests for the vias/traces. All this before I carefully install each socket, testing it is flat/flush with the board. I tend to solder two opposite end of socket pins and once all partly installed I go through each one at a time to ensure they are fully seated again by heating up the two soldered pins. Then I solder each socket fully when happy

 

I'll do the same for the delay line as it needs a socket also.

 

I'll pop pics up sometime this week as and when I get around to it. 

 

Thanks again for all the help everyone. Again the only reason I started this topic was because of the audio tone on boot up and my curiosity as to the cause of it. (I pretty much assumed the RAM and or CPU was at the heart of the main issue/black screen aspect of things, although I apppreciate it can be more complex and multilayered when troubleshooting.)

[_The Doctor__]

just heads up, a bad OSROM can do this also, but it's likely just RAM per usual.

[Beeblebrox]

Sure. It's working with the sram module in place as per yesterday's post so I have no doubt once the sram module is removed, ram/delay chip sockets are in place and non mtram chips installed - notwithstanding any errors with adding in the sockets - all will still work.

[flashjazzcat]

Clearly the OS ROM is working in this case.

 

[_The Doctor__]

inevitably we get another person ghost reading threads with similar issues, so it doesn't hurt to mention after the fact stuff

[flashjazzcat]

Future readers: it's not the generic plausibility of OS ROM malfunction I was commenting on, but this specific case and the cloud of doubt which continues to hang over the fact the RAM is duff.

[_The Doctor__]

On 4/23/2023 at 11:37 AM, TZJB said:

DRAM and CPU is my guess. Some MT DRAM has already been worked on but change out for tested 4164 or 41256 DRAM.

It would seem that is well and truly covered.

 

On 4/23/2023 at 12:24 PM, x=usr(1536) said:

RAM would be my next stop.

 

On 4/23/2023 at 1:24 PM, flashjazzcat said:

it's entirely possible another one has died.

 

4 hours ago, _The Doctor__ said:

but it's likely just RAM per usual.

of course the delay line isn't ruled out, since we haven't gotten confirmation on that yet