Help w/ 800XL and 600XL

[unixdude]

On 3/15/2020 at 12:42 PM, R.Cade said:

I see you still have Micron RAM on that board (MT). In my experience, those are almost always failed or failing.

 

Do I understand that this 800XL passes the self-RAM test (all green) but then still only boots back to the self test? If that's the case, then it could be a ROM problem or maybe possibly the MMU PAL/GAL.

 

Current state:

 

600XL using Sys-Check

- boots to Sys-Check and fails the RAM test (of course)

- boots to qmeg OS

- set to either of the XL/XE options, it boots to a blue screen w/ cursor (no "READY" prompt), then switches over to self-test

 

600XL by itself (no Sys-Check plugged in)

- always boots to black screen

 

800XL: always boots to black screen no matter what: doesn't matter if I'm using Sys-Check or not, the 800XL won't boot.

 

I should note that I had to desolder the OS ROM chip from my 800XL, and I destroyed that one while removing it.  In my testing, I have been using the known good OS ROM chip from the 600XL.

 

I suspect that I burned up the OS ROM chip, and that I need to replace more RAM in the 800XL.  I have ordered some suitable EPROMs, an EPROM eraser, and an EPROM burner, and will try making my own OS ROM chip once those arrive.

 

All the RAM is original except for the one chip that I changed.  All are soldered in except the one that I desoldered.  I guess it's time to cut out all the old RAM chips and solder in sockets, and buy some different RAM chips.

Edited March 17, 2020 by unixdude
Added comment about OS ROM chip

[xrbrevin]

you can try piggybacking the RAM chips with known good ones

[unixdude]

Just now, xrbrevin said:

you can try piggybacking the RAM chips with known good ones

Thanks, yeah, that was the first thing I tried, but it seems that the chips I bought are not known to work in the 800XL. I'll get some new ones and then try piggybacking.

[unixdude]

On a whim, I ran the self test on the 600XL today.  The ROM and RAM both pass.  Would I be correct in assuming that the two ROMs that it tests are the OS ROM and the BASIC ROM?  If so, that would imply that my OS ROM chip is fine and that there's some other reason my previously working 600XL now boots to black screen.

 

The only thing that changed between the time it worked and that it didn't work was that I removed the OS ROM chip from the 600XL and placed it into the 800XL in order to test my RAM repairs.

 

Why would the 600XL boot to self-test when the XL/XE OS is selected in Sys-Check?  Why would the 600XL boot to black screen without Sys-Check connected?  Why would all self-tests pass in the 600XL, but the system won't boot?

[R.Cade]

I *think* the self test does not test the BASIC ROM (not 100% on that) so you can get all green and still boot to self test. I think I had one with this problem.

 

[unixdude]

Well, here's some new info.  I think I just watched a chip die in my 600XL.

 

It was running self test again, and I noticed that the green blocks were turning blue -- to the point that they faded into the background.  Then the display started getting more & more jumbled, then the display turned white.  Now when I power it on, it always boots to black screen.

[mellis]

4 minutes ago, unixdude said:

Well, here's some new info.  I think I just watched a chip die in my 600XL.

 

It was running self test again, and I noticed that the green blocks were turning blue -- to the point that they faded into the background.  Then the display started getting more & more jumbled, then the display turned white.  Now when I power it on, it always boots to black screen.

I know this was brought up earlier, but your various problems across machines suggest one or more power supply issues to me.

[unixdude]

Maybe.  I have the big black one in that picture; I thought those were known good.

 

I found a diagram showing the PS pinouts, and my multimeter shows a steady 5.08V.

Edited March 17, 2020 by unixdude
Updated w/ test results

[unixdude]

It gets even more fun -- I just booted the 600XL again in order to try to do a blind self test -- and it's showing video again!

 

Strange things are afoot at the Circle K.

[manterola]

I don't know if it was mentioned before, but sockets tend to fail (have connectivity problems) if they are to old. My first and only 600xl I got was working when I tried RF. Then installed UAV and started to fail, up to a point of black screen.. I discovered, after 2 weeks of exchanging chips around, desoldering other chips from an XE , ordering PIA in ebay, etc, that the chips were all good. But two sockets were having esporadic or no connection in two pins. I solder a jumper as a temporal fix, and the 600 xl started working again, but with weird colors. After more weeks, I  found another pin in another chip (I guess gtia or antic) was also problematic.

once I look at the socket with a magnifying glass I was able to see a little tiny misalignment in the problematic pin.

The lesson is, check continuity between chips "shoulders" and motherboard or another chip shoulder by following the schematics. I like to print it and use highlighter to mark them.

 

Edited March 17, 2020 by manterola

[xrbrevin]

21 minutes ago, unixdude said:

Strange things are afoot at the Circle K.

 

[unixdude]

It's entirely possible that sockets are failing here.  I think I'll leave the 600XL alone for now, and just concentrate on the 800XL. Maybe the 600XL just needs some better sockets.

[unixdude]

Here's a little bit more information.

 

I forgot that the Sys-Check has the ability to disable internal RAM.  When I use this setting with Sys-Check connected to the 600XL, with the Sys-Check set to XL/XE OS, the 600XL boots to BASIC, not to self-test.

 

When I do the same thing on the 800XL, it still boots to black screen.

[+orpheuswaking]

Remove and reseat all chips several times if you haven't already done so. 

[+DrVenkman]

3 hours ago, unixdude said:

Here's a little bit more information.

 

I forgot that the Sys-Check has the ability to disable internal RAM.  When I use this setting with Sys-Check connected to the 600XL, with the Sys-Check set to XL/XE OS, the 600XL boots to BASIC, not to self-test.

 

I am starting to wonder about your PIA there, or possibly the socket.

[Sugarland]

Yes it could be another chip or the PSU. I strongly recommend using a USB charger as a power supply, as long as it provides at least 1.5A. Yes the black rectangular PSU's are known to be better but they can still fail and it's a very good idea to fully service them before put to use. Keep that PSU. It's valuable and collectable. They are uncommon to say the least.

 

The caps you photographed look okay at first glance but check underneath them for leakage. If you can remove them and test them that is good.

 

[+kheller2]

why you are using the syscheck on the 800xl, you are connecting up the 5 volt line to it right?

 

[unixdude]

Yes, I'm connecting the 5 volt line to the joystick port #2, pin7 I believe it is.

[unixdude]

Here's an update on the 600XL and 800XL.  Perhaps someone here can make sense of these results.

 

The format here is: switch settings, followed by the result of booting the system.  I'm using binary representation for the 5 switches, with the different DIP blocks separated by a dash. I hope you see what I mean here.

 

600XL:

11-110: (Sys-Check as a diagnostic device) Sys-Check starts counting the memory. It fails of course because my system has only 16K RAM. Unfortunately, since the RAM test fails, Sys-Check does not proceed to the OS ROM check.

01-010: (Sys-Check as external OS switcher, Sys-Check RAM disabled, 600XL RAM enabled) System boots to a "READY" prompt

01-011: (Sys-Check as external OS switcher, Sys-Check RAM enabled, 600XL RAM enabled) System boots to a "READY" prompt

01-001: (Sys-Check used only as external RAM) System boots to a black screen

01-000: (Sys-Check disabled) System boots to a black screen

Sys-Check unplugged: System boots to a black screen

 

Since 01-010 boots to a "READY" prompt, and since 01-001 fails to boot, I'm guessing that this points to a bad OS ROM chip.  I bet if I replace that OS ROM chip, the 600XL will boot again.
 

800XL: Testing all of the same configurations as the 600XL: Always boots to black screen.  I'm guessing that this means the 800XL's RAM all needs to be replaced.  I will cut out the old RAM and solder sockets in place, then try new RAM.

 

If it matters, my old RAM is Micron MT4264-15, and the new RAM is KM4164B-10.

 

Thanks.

Edited March 25, 2020 by unixdude