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hueyjones70

130XE troubleshooting

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I have a 130XE that boots with random letters filling the screen and after about 1 second, parts of the screen start rolling like an old TV when the horizontal hold needed adjustment. If I plug in a Star raiders cart, the screen is still filled with letters but it doesn't roll. There seems to be some background screen interference but the screen stays still. Any idea where I should start trouble shooting, this will be tough because nothing is socketed, and replacing chips isn't much of an option unless I want to redo the entire motherboard.

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I would say bad ram.

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I am working on a recently purchased 130XE that appeared to be in good working order. Yesterday when I attempted to run the internal diagnostics the screen went black. I tried to restart it and nothing happened. I determined that it was a heat issue somewhere because it was turned off for a while it would boot up when turned on. After a few seconds the screen would start to flicker then some random characters that appeared to be from graphics mode 1 or 2 would appear and the screen would go black. Today I booted it up and it stayed stable for 6 minutes before exhibiting the erratic behavior. The only chip that gets warm is the CPU. I will start with that but I know it will probably be an aggravating process since nothing is socketed.

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20 hours ago, hueyjones70 said:

I am working on a recently purchased 130XE that appeared to be in good working order. Yesterday when I attempted to run the internal diagnostics the screen went black. I tried to restart it and nothing happened. I determined that it was a heat issue somewhere because it was turned off for a while it would boot up when turned on. After a few seconds the screen would start to flicker then some random characters that appeared to be from graphics mode 1 or 2 would appear and the screen would go black. Today I booted it up and it stayed stable for 6 minutes before exhibiting the erratic behavior. The only chip that gets warm is the CPU. I will start with that but I know it will probably be an aggravating process since nothing is socketed.

Hey good luck with that! I am working on a project that was posted here to replace the keyboard on my 130XE. In opening my 130XE, I discovered that almost all the ram chips were MT ram and they were not socketed (only one was not). Even though my 130XE was working fine, I decided to be proactive and replace all the ram anyway. I added sockets and new ram and all worked out. Maybe down the road I will add sockets for the rest of the chips. Funny enough, my motherboard had some of the chips already socketed.

 

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I have had computers that didn't work because of bad ram but I've never had one that worked intermittently due to bad RAM. I'll probably go ahead and replace it because it is MT RAM and I will just cut out the RAM chips so there is little chance of lifting a trace.

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4 hours ago, hueyjones70 said:

I have had computers that didn't work because of bad ram but I've never had one that worked intermittently due to bad RAM. I'll probably go ahead and replace it because it is MT RAM and I will just cut out the RAM chips so there is little chance of lifting a trace.

With issues likes these, sometimes the only way is via process of elimination. I have an idea. Maybe you can post a picture of the top and bottom of the motherboard. There are a lot of sharp eyed people here. Maybe they can take a look and see if there any physically amiss that can be causing the issue (i.e. bad caps solder joints).

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I removed the RAM, installed sockets and replaced the RAM with non MT RAM. Today I booted it with the Omniview OS and I wanted to see how long it would work. After a few minutes it started changing the letters that were on the screen. Then the screen just froze in place. I tried typing but the computer had stopped operating. I am now in the process of removing the ICs and installing sockets.

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1 hour ago, hueyjones70 said:

I removed the RAM, installed sockets and replaced the RAM with non MT RAM. Today I booted it with the Omniview OS and I wanted to see how long it would work. After a few minutes it started changing the letters that were on the screen. Then the screen just froze in place. I tried typing but the computer had stopped operating. I am now in the process of removing the ICs and installing sockets.

Check the temperature of ANTIC.  If it does this, use freezer (compressed air turned upside down) and see if it works when cold.

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@hueyjones70   Sounds increasingly possible ANTIC is glitching. I could also be a bad pin/leg or solder/trace socket connection related to ANTIC. 

 

I had this with the 130XE I ressurrected from the dead earlier this year. Turned out it was a bad connection with pin 2 of the ANTIC chip, among other issues:

 

 

Definitely check out the temp of the chip as Stephen suggests, and check the ANTIC chip's connection to the board, it's socket, traces coming off the chip. Maybe re-socket the chip itself.

 

Do you have access to anther known working ANTIC?

 

 

 

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11 hours ago, TGB1718 said:

Don't think anyone mentioned PSU yet, have you checked it's around 5VDC ?

Another XE, an 800XL, and two 600XLs work perfectly using the same PSU.

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Definitely look at ANTIC next.  I suggested the freeze trick.  If RAM is known to be good, ANTIC is next logical thing, as it controls the text data that goes to the screen.

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Today when I turned it on I got a screen full of random characters and a rolling screen. I have replaced the CPU and the ANTIC; GTIA is next.

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Every time I turn the computer on, it does something different. Today it booted to self test. If I insert a BASIC cart it boots to BASIC. I thought that the BASIC IC might be bad so I removed the IC, installed a socket and replaced the BASIC IC. Now it boots to self test in black and white except the words "SELF TEST" are green.

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On 12/10/2021 at 12:49 AM, hueyjones70 said:

Today when I turned it on I got a screen full of random characters and a rolling screen. I have replaced the CPU and the ANTIC; GTIA is next.

@hueyjones70  In replacing the ANTIC and CPUs did you also check all the traces and sockets themselves, and/or replace the sockets for both chips?

 

Also the CPU and ANTIC chips you removed - did you pop them into a known working A8 to see if they worked in it?

 

As in my post I linked to earlier, my 130XE had multiple issues - namely:

  • Half the crappy Micron MT ram chips had gone bad, which is the main cause the machine appeared dead all those years ago.
  • A bad via on pin 2 of ANTIC was initially causing screen glitching.
  • The transistor Q3 (2N3904) on the Color circuit from GTIA pin 21 leading to pin 5 chroma of the DIN socket was malfunctioning. 

 

I've found that generally if the RAM has been replaced with known good ram, and the Ram sockets are good, etc, the other issues an A8 might have in these cases will then start to reveal themselves. You find one problem and fix it, there might be another revealed that you wouldn't have known about. This has happened with several XEs and my latest 600XL. Took me many hours and lots of help from individual's on the forum, but I got there in each case. 

 

One of the must have tools IMHO that I regularly use when problem solving and also installing new RAM in XEs is this:

 

4027/4096/4108/4116/4516/4816/4532/4164/4128/41256 DRAM Tester

 

image.thumb.png.e66284f5d4d8641af5c7eb6326ddf63d.png

 

That way I test all new chips I am installing as well so I know I am not installing bad ram. (This has happened before - I bought good brand replacement, (NON MT), RAM chips on Ebay - and of the 8 x bought, 2 x were bad).

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I have checked everything carefully though that doesn't assure that I didn't miss something. I know that I didn't lift any solder rings or traces and I wiped the solder rings with wick top and bottom to eliminate any solder bridges before installing the sockets. I still have a lot of chips to socket but it is baffling. I have another 130XE that is dead and I socketed the entire board and checked every chip and never figured out what was wrong.

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As suggested, PSU issue should be definitely eliminated with good stable 5V, ideally lab-PSU. Use scope if possible to check power glitches following power-up.  Otherwise I would suspect problem on data/address bus.

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I have tested every IC on the motherboard that is common with the 800XL and they are all good. I suppose the problem must be with a resistor, capacitor, diode, or transistor.

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