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Tandy 1000 Shows Random Characters on Startup

Keeganjohn

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Jan 7, 2016
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Hello, This is my first post so i apologize if i do something i'm not supposed to.

I'll be completely honest, i have very little knowledge of vintage computers, but i really want to learn.

Anyway, i have a Tandy 1000 computer that just shows the attached picture on startup. From what I've gathered, the message has something to do with that RAM, but i have not found any information on what the random characters all around the screen are. I also will attach a picture of the board, i took the floppy drive out to show the entire board, but i do have it and i did put it back in before restarting the system after cleaning it.

As for repairs, i have quite a bit of soldering experience and i am very good with mechanical repairs in general, so that will not be a problem. As stated before, however, iv'e never worked on a vintage computer before, so i am not going to know the terminology but i am very eager to learn. Please help, and Thank you for reading!
 

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Lucky for you the ram is in sockets (it's those two columns of eight chips) so you won't have to do any desoldering to change out or test the chips.
The random characters may be the result of the faulty ram. Either way, tackle the ram fault first and see what happens. Try reseating each of the 16 chips as a dirty connection can also look like a failing ram chip.
 
Ok, i took all the RAM chips out, cleaned the sockets and put them back in, and it got significantly worse. IMG_20160106_234434473.jpg i'm sure that i messed them up somehow, so how would i go about testing them?
 
You'll need replacement chips to swap out in order to test them. I would just buy enough to replace it all- they are still made and are available from Digikey, etc.
 
Does the Tandy 1000 has a built-in video adapter? Because, if I am not mistaken, this memory location BBE80:0048 resides in the video memory address space. If so, swapping the video card should solve the issue.
 
Does the Tandy 1000 has a built-in video adapter? Because, if I am not mistaken, this memory location BBE80:0048 resides in the video memory address space. If so, swapping the video card should solve the issue.

The video adapter is on-board, and uses the system memory.
The address is indeed above the 640k range, in the usual video address range. MDA is from B000h to B400h. CGA is from B800h to BC00h.
So this is in the range of memory mapped for CGA compatibility.
I believe it works the same as the PCjr, where a certain page of system memory is mirrored in the B800h range. Which means that system memory is bad, or the circuit that controls the memory remapping is bad (or the system is somehow configured for the wrong amount of memory or something).
 
The bit patterns may be useful...

according to the service manual:

"A 180h byte area of video/system RAM is tested to be used for "stack" and "data" by the CPU. The test consists of writing throughouy the area in the following order all 0000's, 5555's, AAAA's and FFFF's from address BBE80 to BBFFF. [...] If there is a fault in writing/reading any of these data patterns the following fault messages will be written on the screen:

"VID ADDR: BASE: BBE8 OFF: XXXXH"
"DATA FAULT: WRITTEN XXXX READ: XXXX"

When these messages appear the "offset" address should be references. If the offset adress is the top of the range being tested (BFFFE) this indicates that there is no available RAM in the system. The "data fault" message indicates the memory bit that is faulty. For bad bit(s) in the lower byte (even, character), displayed ASCII characters of the message or clear area may be wrong. For bad bit(s) in the upper byte (odd, attribute), the displayed message might have variations such as blinking, color change, and so on.

So, you can try swapping the RAMs from one row to the other and see how the bahavior changes to figure out which is bad.
 
I would have to guess this is likely a bad seated memory chips. I got a similar garbled screen when I purchased some replacement ram that was bad on my Tandy 1000 sx. From the looks of it you have an older Tandy 1000 unit.

Blow out the system with a good air duster, and then buy a new set of memory chips for replacement of the chips located near the front of the case (256K x 1 DRAM at 150 nanoseconds).

Take out all the socketed memory chips (that are in the top left side on your picture), make sure no jumpers are on E1-E2, and no additional memory cards are inserted into the ISA slots and boot to see if you get 256k of memory.

If it does, then replace the memory chips and try again.

Here is details on the memory settings for Tandy 1000: http://support.radioshack.com/support_computer/doc1/1043.htm
 
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I know this thread is really old and i'm sorry for replying after such a long time, i just want to let every one that might be having a similar issue that this did work! Thanks Everyone!
 
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