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Tandy 1000sx quit working.

D

dabone

Veteran Member
Joined
Feb 26, 2009
Messages
1,288
Location
Chattanooga, TN - USA
I had put my sx on the shelf for a while (around a month I guess), and pulled it out today to test a cga to svideo adapter. The machine now only give the following message.

Memory size = 640k

Then after a while it beeps once, then nothing. At first when you power on your can toggle the caps lock/num lock lights, but after a few seconds they stop responding.

It never seeks the floppy disks, and never gets to my XT-IDE bios.

I removed both the XT-IDE and the sixpack I have installed (no mem, just rtc). and still no change, floppies were never accessed.
Tested just the +5 and +12 and they were correct. (5.23 and 12.11)

Any clues? Until today I had no troubles with this machine.

Btw, the adapter works fine with the Commodore 128. Colors are still off, but the pic is nice and solid.

Later,
dabone
 
dabone said:
I had put my sx on the shelf for a while (around a month I guess), and pulled it out today to test a cga to svideo adapter. The machine now only give the following message.

Memory size = 640k

Then after a while it beeps once, then nothing. At first when you power on your can toggle the caps lock/num lock lights, but after a few seconds they stop responding.

It never seeks the floppy disks, and never gets to my XT-IDE bios.

I removed both the XT-IDE and the sixpack I have installed (no mem, just rtc). and still no change, floppies were never accessed.
Tested just the +5 and +12 and they were correct. (5.23 and 12.11)

Any clues? Until today I had no troubles with this machine.

Btw, the adapter works fine with the Commodore 128. Colors are still off, but the pic is nice and solid.

Later,
dabone
Click to expand...

Very odd. The 1000SX is usually bullet proof. Try checking the PS again while its under load (carefully). Also, gently apply pressure on the RAM and all chips which are socketed. Double check all of the cabling.
 
Removed and reseated every socketed chip in the thing (except for one plcc that I don't have an extractor for and it's in there tight), tried with no floppies, 1 floppy, xt-ide, nothing.

I forgot to grab my meter to test the voltages, does anybody have the pinout of the power supply connector?

Later,
dabone
 
dabone:

Send me a PM with your email address and I can forward the SXTECH.PDF to you. (Its too big for the forum).
 
Ok, grabbed my meter and All the voltages look good. Switching to ac, I'm not seeing ripple on the DC. I tried swapping the floppy cable for a twisted one and setting the drive for ds1, still nothing.

The machine seems to post fine, but hangs when it should be booting from floppy.
I.e. Turn on, ram is counted. (If I remove ram the machine will show the ram errors in post.) Then the machine beeps once and hangs.

So far I have.
Reseated all socketed chips.
Cleaned the pins on all the 40 pin chips.

Replaced the 4164's, swapped the 41256 bank 0 and 1 with each other. Tried only 1 floppy, tried no floppy, tried no floppy controller chip.

Later,
dabone
 
dabone said:
Ok, grabbed my meter and All the voltages look good. Switching to ac, I'm not seeing ripple on the DC. I tried swapping the floppy cable for a twisted one and setting the drive for ds1, still nothing.

The machine seems to post fine, but hangs when it should be booting from floppy.
I.e. Turn on, ram is counted. (If I remove ram the machine will show the ram errors in post.) Then the machine beeps once and hangs.

So far I have.
Reseated all socketed chips.
Cleaned the pins on all the 40 pin chips.

Replaced the 4164's, swapped the 41256 bank 0 and 1 with each other. Tried only 1 floppy, tried no floppy, tried no floppy controller chip.

Later,
dabone
Click to expand...
Well, assuming it was like you said - working okay when you put it up, and you didn't drag behind you tied to your bumper, its got to be something to do with the cabling or that your floppy drive took a shot. It is POSTing and you see 640 KB. Do you get a light on the floppy when the machine POSTs, and can you hear the floppy spin up? Take a look at the voltage right at the floppy. Check the floppy data cable. Can you check out the HD in another system? Also, pull the 6-pak until the system comes up. Try booting with the floppy disconnected (power & data cable).
 
I've tried no cards, drive a lights only on power on and reset.(Hold the reset button the light stays on.) No floppy spins. Right now I'd love to know what another sx does with no floppies attached. I beginning to suspect my disk controller chip because of some strange discoloration on the chip legs. Brown/Dark Brown and white???? Scrapes off but wtf?
The SX if I remember uses drives that you have to set the jumper on, so I also tried another floppy cable from a more modern machine that had 1 edge connector, and a twist. I set the drive to ds1 for the twist. Still got the same result.


So for testing currently I have the base machine only + floppies (a is a 720, b is a 360 I have tried swapping them). Replaced all ram in use. When the XT-IDE controller is in it never gets to the bios, One thing I forgot to mention is that it never gets past the 40col memory init to the 80 column mode.


Later,
dabone
 
sounds like oxidation to me, the brown and white stuff. Agreed, maybe that is the problem or the controller is not working. Looking forward to hearing further exploration.
 
This problem sounds very familiar! I had a then 6 month old Tandy 1000 way back in the 80's. Was doing the same thing. Well to make a very long story short it turned out to be the Data seperator chip.

If you look near the FDC a large 40 pin chip number 765 you might see a small 8 pin chip with the number WD9216 on it at location U38. That's what was knocking mine out. How I isolated it was using component cooler. I sprayed it on the chip and the floppy started working until it heated back up and stopped working. I had to order a replacement chip. After it arrived I put it in the 1000 and afterwards it was working like a champ!

As quoted here:

The bulk of the FDC interface is handled by the 765
controller chip and the 9216 digital data separator. The
765 generates write data which has pre-compensation added by
U50. Read data from the floppy drive is separated into data
and clock for the 765 by the 9216 data separator.

This was taken from the 1000 sx technical reference manual.

Available here: http://www.oldskool.org/guides/tvdog/documents.html look for file sxtech.zip

Something you might want to check or as others have said maybe tge FDC itself. I hope this helps out.
 
Last edited:
Chromedome45 is right. Once you run out of common sense options then you have to bite the bullet and try some troubleshooting. A can or two of freeze spray may get you in the ballpark. Also, I woundn't make a career out troubleshooting that mobo as they are plentyful and cheap. Good luck.
 
Ok, right after I ordered the chip I remembered I had a Coco controller in the corner, It had a wd9216 in it. Swapped for the tandy one, still no change.

Later,
dabone
 
Hmm. Check the contacts of the chip that you swapped, see if you can do something to really clean the contacts there. There is still copper in there, it can oxidize. It's tedious but that would be my next step.
 
Next thing might be to swap the NEC 765 Floppy controller if you can find one. Also just FYI the Intel 8272 is a pin compatible replacement.
 
Found another, nicer shape 1000sx at a computer recycler today. 25.00 cash and carry. 2 5.25" and nothing else in it.
Don't know if it works yet, but if not, more spare parts.

Later,
dabone
 
%#*(&@W#(*%&^(@#*%^(@*#^%*(^Y!!!!!!!!

The new to me SX wouldn't turn on, I removed the hardcard that was in it, and it then turned on, but black screen. Swapping chips between my first unit I found that u51 (IC CPU Support (Lt. Blue)) was bad, but the one from my first unit duplicates the error the first unit has in the second! (Memory test, single beep then hang.)

So now I have 2 1000sx's with no working VGC7205-0409 custom ICs.

Anybody have any good ones of these chips for sale? cheap?

Later,
dabone
 
Don't panic yet. Check over the mobo real good. Make sure that the DIP is set right for the video - the SX has a setting for onboard CGA (on/off). What type of video setup are you using? Do you have an add-in CGA/EGA/VGA 8-bit ISA card?
 
No add in card, hooked to a cga monitor, trying to boot off floppy for trouble shooting. All dip switches are set to on.
List of the 4 dip switches and their functions can be found here.

ftp://ftp.oldskool.org/pub/tvdog/tandy1000/documents/swblk.txt

One of the U51's is completely dead, I get no post what so ever.
Apparently this is a custom chip for this machine only because I can find no reference to the chip number anywhere else.

Any other 1000sx owners out there that would let me send them my semi working chip for them to test in a known good machine?

Later,
dabone
 
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