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XEGS Fails ROM test - Fix Advice?

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Hi - I am seeking ideas and advice how to troubleshoot an XEGS that is failing the built-in ROM test.  Thanks for any and all ideas. Go easy on me… I’m new but learning to repair A8bits.

Questions:

 

1) Is the first action to replace the ROM?  OR are there other things I should check first?  I am using modern known good power supply. 

 

2) If I must replace the ROM where can I get a known good replacement?

 

3) Does anyone sell replacement ROMs or do I need to pull from another system?

 

4). If pull from another system must it be an XGES (verses from any other A8bit)?  I assume it must be from XEGS given the unique features. 
 

image.thumb.png.98bacc1894fcd08142322cf99fe23687.png

 

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The OS ROM on an XEGS is a common failure point. An 27C256 EPROM is a pin-compatible replacement, though it will require desoldering the original. To prevent damage to the motherboard, this is probably best done by just clipping off the pins, and then each pin can be individually extracted.

 

The XEGS combines the OS ROM, BASIC and Missile command onto a single 32Kx8 ROM, instead of most other XL's/XE's which have a separate 16K OS + 8K BASIC ROM - so they cannot be used.... Well - if you must, you might get an XEGS to boot for a quick test with the ROM from another XL/XE, but you'll not have a working BASIC or Missile command.

 

if you PM me I can mail you a programmed replacement chip + socket.

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51 minutes ago, Nezgar said:

The OS ROM on an XEGS is a common failure point. An 27C256 EPROM is a pin-compatible replacement, though it will require desoldering the original. To prevent damage to the motherboard, this is probably best done by just clipping off the pins, and then each pin can be individually extracted.

 

The XEGS combines the OS ROM, BASIC and Missile command onto a single 32Kx8 ROM, instead of most other XL's/XE's which have a separate 16K OS + 8K BASIC ROM - so they cannot be used.... Well - if you must, you might get an XEGS to boot for a quick test with the ROM from another XL/XE, but you'll not have a working BASIC or Missile command.

 

if you PM me I can mail you a programmed replacement chip + socket.

Wow!! Thanks for the offer!! I sent you a PM.  Also, could you add a picture of the location of the XEGS ROM chip.... just so I don't desolder the wrong one 🙂  Thanks!!

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If you havent tackled an XE PCB before, you should be aware they are not as durable as their predecessors and tracks can lift (Tramiel saved on manufacturing costs..!)

As Nezgar recommended - the chip is toast anyway so snip the legs so that the remains are much more easily removed 😎

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It only has the one Rom so there's not really other option than replacing it assuming it jumps into Self Test every time with no ability to boot from disk (a diag mode cartridge like a Star Raiders cart would probably work on it)

 

Though given it's only failing in one half, worth checking the connection of the high address bit that goes to the chip.

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14 hours ago, Rybags said:

It only has the one Rom so there's not really other option than replacing it assuming it jumps into Self Test every time with no ability to boot from disk (a diag mode cartridge like a Star Raiders cart would probably work on it)

 

Though given it's only failing in one half, worth checking the connection of the high address bit that goes to the chip.

Great News!  after a lot of cart wiggling and on/off cycles Star Raiders works great!  Joystick and keyboard work too (at least all the keys that SR uses). So once I replace the ROM chip this XEGS should be good. 
image.thumb.jpeg.6bbb1deca04a57a84875e7d33ec7b985.jpeg

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Posted (edited)
On 7/31/2021 at 5:56 AM, xrbrevin said:

If you havent tackled an XE PCB before, you should be aware they are not as durable as their predecessors and tracks can lift (Tramiel saved on manufacturing costs..!)

As Nezgar recommended - the chip is toast anyway so snip the legs so that the remains are much more easily removed 😎

 

Along with chips going bad, what about the possibility of solder joints wearing out? I recall the tale of someone turning on the oven to 350 degrees and letting a motherboard roast like a tray of cookies for a while... and it worked. All golden brown and--  

 

--eureka, found it!

 

https://www.techtipguru.com/how-to-bake-a-motherboard/

https://www.computerrepairtips.net/how-to-reflow-a-laptop-motherboard/

etc

 

Still seems obscenely dangerous, especially as all the plastic-encased microchips need to be covered to prevent too much direct heat...  has anyone even tried doing that sort of thing?! I'd be hesitant, unless absolutely nothing else worked. But if it fails, you can flush it and say "Chips ahoy!"  bah-dah-bump... :(

 

 

Edited by CommodoreDecker
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Posted (edited)

That method of baking was done for surface mount BGA repair... the balls of solder in grid arrays under the chips cracked... it was easy enough to insulate most items that didn't need the heat and carefully tape the bga chips so they would heat and reflow properly without sliding out of place when baked... XBOX repairs were done this way en masse.... not the method for most other chips and older pcb's however...

Edited by _The Doctor__

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A newly acquired XEGS with issues landed me on this post while searching.  Keyboard is working fine, I get BASIC, but when trying cartridge games I found that controller port 2 fails to register directional movements although fire button works (tried swapping controllers and same results). Before checking solder points etc. I tried the self test starting with memory.  ROM bar 1 is bluish/green but then right after ROM bar 2 flashes the screen goes blue and then just stays like that. Sound and keyboard are both OK.  I tried to get Missile Command by the Select/Power button method as well as without keyboard attached but I just get a blank screen. Guessing the ROM is shot for sure?  OEM power supply was working but used new power supply as well with same results.  Thanks!

IMG_5048.JPEG

IMG_5047.JPEG

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do a continuity test on the controller port pins. i had a snapped pin in one once, obviously caused by a previous owner's heavy-handed actions

does the controller work if you wiggle the plug in the port?

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I'd say ROM... or ram...  if the rom bar turns green before the blanking... ram bad

If you don't see green, but red on rom bar ... rom normally bad

if It never shows either then it could be rom ram or both

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If the RAM were bad but the ROM good should Missle Command still load? The seller confirmed Missle Command worked before shipping but the package was a little loosely packed so I think it got knocked around a fair bit in transit with likely friction from all the included pieces.  I have an U1MB that was planned for my first Atari 8-bit system 800XL but maybe the XEGS will need it.

 

I'll pop it open to see if port 2 pins are soldered and have continuity. Seller couldn't recall ever playing anything 2 port.

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If your ram has the letters MT on it, it needs to go. Those are cheap ass Micron Technologies' rams that do not reset.. they hold chunks of data after power down.. they sorta act like static ram. Pull the chips, put in a socket and install new ram. Another Tramiel cost cutting measure. They knew they had bad rams because I have seen them in 800XL's.. but they would put ONE Japanese ram in the first slot closest to the power, and the rest MT... and Yes.. those single layer XE boards are cheap as hell and it's easy to pull up a trace. Many times I have just cut the chip out, then took my time cleaning up.

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I have an XEGS motherboard with a goldish-brown soldermask that is of a very good quality. I've removed the ROM and nearly every 40 pin chip without ever disturbing or damaging a trace using only an iron and solder sucker.

 

Edited by mytek

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Busted it open today. Has the goldish board. Solder points look good on controller port 2 with continuity on all pins, wiggling did not help still only fire button working.  So with this issue, Missle Command going to black screen, Memory test going solid blue after 2nd ROM bar lights up white, where should I start to socket and swap fun? 

 

30ABBAC8-3212-45EE-B437-3082D9653912.jpeg

36628BB8-7170-45B3-A42D-C8CCC70AF0F5.jpeg

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Be aware of the relationship between the ROM and MMU.

When recently fixing a 65XE, i found the MMU has a signal line connected to the ROM to enable it on power-up. The MMU was faulty - it didnt send this signal and thus prevented the fully working ROM from kicking in. it caused a potential 'red herring' situation that couldve implicated the ROM was at fault!

 

Looking at the XEGS schematic, pin 15 of the MMU is "OS" and it goes to 2 pins on the ROM: pin 20 "CS" (chip select) and pin 22 "OE" (output enable). If you can determine if the logic requires 0v or 5v you can test if its faulty.

 

If so, the MMU can be replaced with a low cost programmable PAL or GAL chip - cant remember which but there are topics on here that go into more detail

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1 hour ago, eems said:

Busted it open today. Has the goldish board. Solder points look good on controller port 2 with continuity on all pins, wiggling did not help still only fire button working.  So with this issue, Missle Command going to black screen, Memory test going solid blue after 2nd ROM bar lights up white, where should I start to socket and swap fun? 

 

 

36628BB8-7170-45B3-A42D-C8CCC70AF0F5.jpeg

 

Beautiful board! Seeing a lot of cold solder joints (?) on the top side of the board, however.  CPU & Pokey in particular. Maybe the joints need some love.

 

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It is pretty and been nice to work on so far. Socketed the RAM (ordered a few replacement) and Pokey yesterday and awaiting sockets for the OS and MMU slots. I'll be prepped for trying U1MB, and hit the other chips with fresh solder when the sockets come in. Pin 40 on the Pokey was missing piece of leg but looked like it was connected to board enough. Hakko solder pump and hot air station made for "easy" chip removal. Easy for novice anyways!

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Well I got the sockets all in, hit all the old solder on the rest of the solder joints with fresh solder and popped old chips in to test that I'd get same results as original issue but things seem to have gone from bad to worse. Now the green led will not light and there is no video/sound output at all or even static. 

 

Since I cannot tell if power is on I checked the left side of the power connector for 5V and can see 5V to the L3 regulator and then at the switch but everything after that is out of whack.  Tracing from the center point on the switch their is continuity up to the C13 etc. but no voltage.  Probing some of the chips I see 1 to 2 volts on some pins so there some power out in the board but none making it to the LED for sure.  Not seeing any shorts on the fresh solder joints.  Without a Field Service Guide with flows diagrams for troubleshooting I'm not sure where to go next.  Any pro tips with how to go about this new issue aside from getting a new board? Thanks.

 

XEGS_p9.thumb.png.e1511a5d176e18def4c35ce246db3930.png

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