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Tandy 1000SX not POSTing, thoughts?

A

ardsleytank

Experienced Member
Joined
Nov 15, 2015
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282
Location
Tennessee
Hi all,

I have just purchased a Tandy 1000SX that was untested, and upon taking it home, I have found that it will not POST. No beeps at all, though the floppy drive light came on (and stayed on), the caps-lock lights are on (and unable to be turned off) on the keyboard, and the screen is filled with pulsating green bars.

I tested the voltage coming out of the PSU, and everything seems within spec. I even pulled all the RAM chips to see if anything would change. It did not.

Any thoughts on how to proceed? It's in pretty good condition, and I'd like to get her going again.

Many thanks, it's good to be back.
Peter
 

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Slight update: I tested continuity between the 5V pins on the motherboard where the power supply plugs in, to ground, and am seeing 50oms. My meter thinks that is pretty much a short.

Would any of you be willing to check your machine to see if that is a normal reading?
 
ardsleytank said:
Slight update: I tested continuity between the 5V pins on the motherboard where the power supply plugs in, to ground, and am seeing 50oms. My meter thinks that is pretty much a short.

Would any of you be willing to check your machine to see if that is a normal reading?
Click to expand...
I can check mine later today.
 
Double check that someone else hasn't plugged in the cpu/bios/anything else in backwards.

Check the rams and see if any feel hot compared to the others.

Also check the video rams for the same, these are located in between the cpu and the large chip at u30.


On my 1000sx I had U51 fail, which causes a lot of issues.

Here's a page that I found that has some troubleshooting for the sx. Click Here
 
Hello all,

Thank you for all of your suggestions. I have repeated  all the chips at least once, maybe twice, no change. I have tried to identify any buggered ram chips, nothing has changed.

I swapped the cpu for a V20, no change. Nine of the chips get hot, the cpu only gets ever so slightly barely warm.

It appears this is much bigger than I thought, and I'm thinking one of the Tandy chips probably died. Likely U51 as somebody suggested.

Since I lack a oscilloscope and appropriate knowledge, I'm likely just going to have to find another main board.

Thank you for all your help,
Peter
 
I've got a 1000 sx board here, minus the u51. it's untested, but you are welcome to it if you are in the area. (I'm in Chattanooga.)

Or, you can send or bring your u51 and I'll test it in my working 1000sx.
 
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