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sh0dan
July 11th, 2017, 12:32 AM
Im afraid this is my first post here and Im already after help, sorry!

I bought a Zenith ZF-150-52 off a lovely chap who had owned it since he purchased it new. I promised I would give it a good home and I intend to try.

With that in mind I would be very grateful if anyone can help. The previous owner sold it noting that it booted and showed a ram failure.

Having got it home and wired it up I booted it to a *** ERROR: RAM failure! Address 0000:XXXX, Bit X, Chip U407 *** error. The exact address and bit appeared to change each time. Although, oddly usually starts with the same address after a break in testing 0000:17DA.

It had a hard drive, rambank expansions etc fitted which I removed and still got the same error (U407).

I located the memory chip labelled U407 in bank zero on the standard zenith memory board and swapped it with one in bank 4, same error (U407).

I tried the memory card in a different slot on the backplate, same error (U407).

I tried changing the dip switches on the CPU board from 640k to 128k of memory, same error (U407).

I removed the memory card entirely, same error (U407) however the address is 0000:0000.

I noticed the clock cards battery had leaked and so have removed the card. There is minor damage to it and to a screw on the backplate but I cant see any damage to other cards or the backplate circuits and so have discounted it as a cause for now.

Along the way I tried pressing on each of the socketed memory chip to see if anything was loose etc

It feels like U407 is a red herring? The manual seems to imply its a "guess" as opposed to definite failure - "If standard memory cards are being used, the chip number displayed shows which memory chip is most likely to have failed."

The only thing I havent done to date is change all the memory chips in bank 0 with another one. I'm worried I might cause more damage than good but will do it if it might help the issue.

I have attached pictures of the cards. I dont know what the hard card is, although have matched the circuit board on the hard card to a Segate ST11R from pictures online. I also know little at the moment about the other cards although do have a lot of the original manuals.

I have read through this thread and while interesting it couldnt see a resolution to my problem http://www.vcfed.org/forum/showthread.php?54392-Zenith-151-Trouble/ .

Any help or advise will be very much appreciated.

Thanks

retrogear
July 14th, 2017, 09:55 AM
The numbers across the top of your memory card are the data bits. U407 indicates a problem with bit 2. Try exchanging the chips in the bit 2 column with a bit in a different column but not P. The P column are the Parity chips.
Try exchanging the P chip in the U407 row with a bit in another row (not 2). Keep booting up to see if the error changes.

Larry G

sh0dan
July 14th, 2017, 11:28 AM
The numbers across the top of your memory card are the data bits. U407 indicates a problem with bit 2. Try exchanging the chips in the bit 2 column with a bit in a different column but not P. The P column are the Parity chips.
Try exchanging the P chip in the U407 row with a bit in another row (not 2). Keep booting up to see if the error changes.

Larry G

I had a potentially bad idea before seeing this reply.

I tried swopping everything in bank 0 with bank 2.

I then reasoned that each "bank" was 64 bytes and the cpu board configuration let me select 128 bytes. Therefore, I took out all the memory chips in banks 2-4 and swopped all the memory chips in banks 0 and 1 with them.

I'm now in a worse position generally, I get U407 address 0000:0000 bit 2... basically the same as not having the memory board fitted, zero being the address.

Is there any logic in my choice to remove banks 2-4 and set the memory to 128kb?

If not I could try putting everything back and try your suggestion? Your help does make sense and I can now see the numbers and P across the top.

I'm a little worried I've totally knackered it now? :(

retrogear
July 14th, 2017, 01:47 PM
No you haven't knackered anything as long as you didn't put any chips in backwards or fold the legs.
I would just leave as is and move on. Is there a service manual anywhere? Since your errors focus on bit 2 the problem must be on the data bus somewhere.
Many chips parallel the data bus, even others besides memory. I own and troubleshot memory issues on my Zenith Z-100 and finally resolved it on this forum which is a similar concept.

PS - I see from your photos the edge connector on one of the memory cards looks dicey. Did those clean up?

Larry G

sh0dan
July 14th, 2017, 02:22 PM
No you haven't knackered anything as long as you didn't put any chips in backwards or fold the legs.
I would just leave as is and move on. Is there a service manual anywhere? Since your errors focus on bit 2 the problem must be on the data bus somewhere.
Many chips parallel the data bus, even others besides memory. I own and troubleshot memory issues on my Zenith Z-100 and finally resolved it on this forum which is a similar concept.

PS - I see from your photos the edge connector on one of the memory cards looks dicey. Did those clean up?

Larry G

Thanks for continuing to help, I do really appreciate it. I'm also starting to learn some things!

I have a Z-100 series operations manual which has a hardware section but surprisingly little information in it. There is a collection of Z-100 series service manuals here: http://www.minuszerodegrees.net/manuals/Zenith%20Data%20Systems/Zenith%20Z-150%20PC%20Service%20Manual.pdf

That pdf on the other hand contains a lot of information and its going to take me some time to work out if there is anything of use in it :)

Only the core boards (memory, cpu, video, disk) are in while testing at the moment. The bit that fits in the ISA slot (Im assuming the "edge connector") is not good on the rambank expansion, although the rest of the board is ok. The edge connector on the memory board was ok but I've also used a little sandpaper on it to clean up the contacts.

Thanks again

Mike

sh0dan
July 14th, 2017, 02:37 PM
In fact I've just found the linking page for that service manual: http://www.minuszerodegrees.net/manuals.htm#Zenith