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Tandy 1000H Won't Boot! Weird error message

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bobba84

Veteran Member
Joined
Jan 6, 2014
Messages
560
Location
Melbourne, Australia
Hi guys,

I've just bought my first Tandy, a 1000H. I knew it didn't work when I bought it, but I can't understand the error code it's displaying:

tandy.jpg

This appears instantly when power is switched on. I've done a google search and all I found was info on beep codes - there are none on mine.

Any ideas?

Thanks in advance for any replies.

Bobby.
 
You mean 1000HX, right?

It looks like a RAM problem. Normally this message would show the addresses of the failing RAM chips, but in this case the failing RAM may be in the part that is used for the video, thus corrupting the text.
 
Thanks for replying :)

Progress, it was RAM. Now the onboard RAM is fine, the expansion card has bad ram too!

I removed the second 128k off the expansion board, leaving just the soldered-in 128k, but it seems the problem is in those soldered-in ones.

Rather than desoldering all of them, can anybody suggest which chip it may be from the error message below?

IMG_1027.jpg

Edit: Ignore the bottom line, it was a rolling test, it was just on that address when I took the picture.
Another Edit: Sorry! I got my letters wrong. It's a 1000A!
 
I think you have four bad RAM chips in the soldered bank. Here is my reasoning :

The Tandy is writing a two byte value at every other memory address. The lower of the two bytes always appears correct. This suggests that the memory is interleaved on the Tandy 1000, odd bytes go to one RAM bank, even bytes go to a second RAM bank.

Each RAM bank is composed of eight DRAM chips. Each DRAM chip stores one bit of a byte. Converting the high bytes to binary gives the following :

Written A5 = 1010 0101
Read 8E = 1000 1110

Written B1 = 1011 0001
Read 9A = 1001 1010

To pass the memory test, a bit must read back what was written. The bits that do not match indicate failing memory chips. In your case, bits 0, 1, 3 and 5 seem to be bad and the chips which correspond to those bits must be replaced.

Of course, the Tandy memory expansion board uses 64Kx1 bit RAMS and I am not sure how they correspond to the memory error. I would suggest removing U27, U28, U30 and U32 first, then followed by U19, U20, U22, U25.
 
One last point, why do I prefer U27, U28, U30 and U32 to U19, U20, U22, U25?

This is because U27, U28, U30 and U32 are connected to the addressing logic by RAS1 while U19, U20, U22, U25 are connected by RAS0. Since your problem seems to be with odd bytes and the memory board is arranged in two or four 64KB banks, I figure the odd RAS strobe signal to be the likely culprit.

Ideally you remove all the soldered RAM chips, good and bad, and install sockets. Get your flush cutters, cut the pins near the plastic packages, add some solder to heat up the pins and remove the pins with needle nose pliers, use a heated solder sucker to clean out the holes. Then install your sockets and get some chips and enjoy a board that will not fail you for years to come.
 
My 1000HX memory expansion was very touchy about how the connector was seated on the board... try rocking it back and forth (shouldn't take much force), maybe leaving it pushed down or pulled up a little, to make better contact.

Some contact cleaner on the connector probably wouldn't hurt either.
 
HoJoPo said:
My 1000HX memory expansion was very touchy about how the connector was seated on the board... try rocking it back and forth (shouldn't take much force), maybe leaving it pushed down or pulled up a little, to make better contact.

Some contact cleaner on the connector probably wouldn't hurt either.
Click to expand...

This actually did something! The error changed from all the FFFx ones to just three, being two 6xxx and one 4xxx - if the other error went away maybe the RAM chips are okay? I'll get back to it today with some cleaner and see what happens. Thanks!

On a side note, the power supply wouldn't spin up my ST251. Is it just too weak?

Bobby.
 
bobba84 said:
This actually did something! The error changed from all the FFFx ones to just three, being two 6xxx and one 4xxx - if the other error went away maybe the RAM chips are okay? I'll get back to it today with some cleaner and see what happens. Thanks!
Click to expand...

On my HX it was throwing a page full of errors like yours, then only a few, then once I had the card completely seated, it passed the memory test. So, you may not have any bad RAM at this point, just dirty contacts. Of course, it's still possible you have a bad RAM or two. If you have the Tandy memory expansion, there are two banks, one 128k and one 256k. The 256k is eight 41256 256kx1 RAM chips, the 128k is in four 64kx4 chips, if I recall correctly.

A V20 chip is a good speed up for the 1000HX once you have it working, about 30% faster. You would have to disassemble the computer to swap the CPU, though.
 
Thanks guys! After cleaning the card contacts, all is well.

The ST251 works in another machine, maybe it's just too power hungry! I've got a 3.5" Miniscribe 20MB somewhere, might try that.

Thanks for all your help!!

Bobby.
 
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