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Tandy 1000 TL/2 with Issues

G

Gramcon

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Joined
Aug 30, 2014
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Hello all, I have a Tandy 1000 TL/2 that is virtually pristine on the inside, but unfortunately I cannot get it to work. I don't have a Tandy monitor, so I plugged it up to my IBM 5153 and get the the messed up display like you can see in the attachment. I can faintly make out "Memory Error Info" or something like that in the background. Has anyone run across this before? I'm assuming I have 2 problems -- one with the onboard display adapter and the other being bad memory chips, or maybe it's all one problem. Does it have anything to do with using the IBM CGA monitor? I would try an 8-bit VGA card (or 16-bit card that would function in an 8-bit slot) but do not have one on hand. I'm unwilling to purchase one if that won't fix the problem. Was hoping someone more familiar with Tandys could assist. Thanks!
 

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Looks like a video memory chip may be bad. If thats onboard video it may share the system memory....you should be able to tell by looking at the
motherboard closely and identify if there is a 'bank' of memory chips that could be for the video. Is there a jumper to disable the onboard video
and plug in a video card, like an IBM CGA ? Trying a different video card is probably the fastest way to see whats wrong.

Posting a hi-res picture of the motherboard would help on figuring out where the video memory is located......
 
Thanks for the replies! I have a question about replacing the memory, as anything pre-SIMM era predates me. The DIP chips currently installed are KM44C256AP-10 modules (the 100ns ones). I'm having trouble locating those. Can I replace them with the 80ns versions (KM44C256AP-8) or will the motherboard reject them?
 
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Gramcon said:
Thanks for the replies! I have a question about replacing the memory, as anything pre-SIMM era predates me. The DIP chips currently installed are KM44C256AP-10 modules (the 100ns ones). I'm having trouble locating those. Can I replace them with the 80ns versions (KM44C256AP-8) or will the motherboard reject them?
Click to expand...

Same speed or faster is the general rule, so 80ns should be just fine.
 
wesleyfurr said:
I think most (if not all) of it is here - http://www.oldskool.org/guides/tvdog/faxback.html

I started to try to grab a copy recently, but couldn't seem to find a good index starting point at which to point a web downloader...
Click to expand...

Just connect to it via FTP: ftp.oldskool.org Much easier to grab an entire directory.

To the OP: You only have a memory problem; your monitor and Tandy video output are working correctly.
 
Thanks very much everyone, I will order replacement memory and see if that fixes the problem. Will let you know how it works out!
 
Trixter said:
Just connect to it via FTP: ftp.oldskool.org Much easier to grab an entire directory.
Click to expand...

Sorry, should have been more clear...I meant copying off straight from the Radio Shack site...at this point, that's the one I'm more worried about disappearing...though if everything truly is on tvdog's site, then we're good...

Wesley
 
Well, I replaced the memory with 80ns chips and its doing the exact same thing. I'm starting to wonder now if the EEPROM is corrupted. I don't know what else to do -- I removed the EEPROM and placed it on a "flat metal surface" to discharge it, but I highly doubt this will even do anything. Seems unlikely. I'm gonna keep trying though; this machine is too nice to just toss out.
 
Hopefully this will sound encouraging, rather than discouraging, but the wrong chips were replaced. If vidram failure is indeed to blame, the fault is in one of the four, 64K x 4, 120ns video memory chips, located at U39, U40, U41, and U42. These are found beneath the power supply.
 
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Cloudschatze said:
Hopefully this will sound encouraging, rather than discouraging, but the wrong chips were replaced. If vidram failure is indeed to blame, the fault is in one of the four, 64K x 4, 120ns video memory chips, located at U39, U40, U41, and U42. These are found beneath the power supply.
Click to expand...

Aarrgh, thank you, that is humbling. I was pretty excited until I removed the power supply and saw that the video RAM chips were soldered in, not socketed. That must be why they didn't show up on the system board diagram on the website. I'm not going to attempt to replace those except as a last resort. Will adding a VGA card cause the system to disable the onboard video RAM? I'd rather be willing to try that, though I was really hoping for some Tandy video goodness.
 
It sounds like you've probably expanded the system to its full, 768K memory complement, in which case, yes, the video chipset and its 128KB of memory are effectively disabled by the addition of a VGA card. If the 128K memory expansion chips are not installed, the video controller maps any "unused" portion of the video memory into the address space between 512K and 640K for system use. This would not be an ideal situation to be in, given a presumably bad video memory chip... :)
 
Thanks for your time Cloudschatze. The 128k expansion chips are not installed. So it sounds like I need to get those first, in which case the video will move out of the bad memory into the expansion, and at least I'll be able to see the picture.

However, I'm assuming the soldered-in 64k chips will still fail POST. And, if I'm reading the website http://support.radioshack.com/support_computer/doc1/1222.htm correctly, the 128k expansion chips can only be used for video memory, in which case adding a VGA card would disable the expansion chips, and I'd still be stuck with the bad, soldered-in ones...I hope I'm wrong!
 
You're reading it correctly - it's just that it's incorrect information. :) Installing the memory expansion alone will not solve the video issue, since that memory isn't used by the video controller.

Can you try something dumb for me though? The backplate of my TL/2 chassis likes to grow zinc whiskers. If your system is similar, I wonder if you might just have a short between pins on one of those video memory chips. The whiskers are water-soluble, so you might take a wet Q-Tip and wipe the IC legs. I'm not expecting a miracle or anything, but who knows...?
 
Well, I took the motherboard out and cleaned everything really well with alcohol, no dice. I'm going to see if I can find a VGA card to put in there to see if I can get a readable display. I'm going to try to find a 16-bit one that will work in an 8-bit slot, as everything 8-bit on EBay is way too costly. I'll keep you posted!
 
I tried adding a VGA card, a Trident TVGA8900D-R jumpered to work in an 8-bit slot. The machine doesn't even recognize the card, output still goes to the onboard video. I found another post on this forum from someone using this card in a TL/2, so I know it should work in this machine. I tested the card in 16-bit mode in a 486, so I know the card is not defective.

My last ditch effort (before attempting to de-solder and replace the onboard video memory) will be to populate the memory expansion slots and see what that does. For that, I will have to wait for memory to arrive from Poland. It was cheaper that way...
 
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