Rescuing an Ebay "for parts or spares" 520STFM board

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Elethiomel
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Rescuing an Ebay "for parts or spares" 520STFM board

Post by Elethiomel »

When I was preparing to build my Phoenix H5C1, I mistakenly thought that the donor board I had was unusable. I browsed Ebay and found a board in its shield for £40 marked as not working. I figured that for £40 I could give it a shot and at least get some good chips off it. After ordering it I figured out I COULD use my original donor board for my Phoenix, so I went ahead and did that.

That left me with a board that outputted this on the screen

20220415_164002.jpg
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I had a gut feeling it was RAM related as the shifter was obviously running and had been at least partly programmed. That meant ROM, CPU, MMU, GLU etc were probably OK.

20220415_163844.jpg
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Apart from a little bit of dust and the odd removal of part of the shifter shield (maybe a marpet was previous fitted? - The MMU still had a clip though...) , the board looked to be in pretty good pretty good shape with nothing obviously wrong. I reseated all of the socketed chips to no avail. No chips getting hot to the touch.

I then grabbed my trusty Exxos diagnostic cart and booted up.

20220415_164410.jpg
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A red screen is looking good. I'd expect that with no keyboard attached. Time to look at the serial console.

20220415_184721.jpg
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Looks like my intuition was correct! We have a bogey RAM chip. Looks like it's the one for bit 5.

20220415_165538.jpg
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Now which chip is that!? It could be the 6th chip in the first column, counting from the top. It could be the 6th in the 2nd column counting from the right. It could go left to right, then down. It could go any number of ways to be honest. I could try and sound things with the schematic, but I had a simpler idea.

I grabbed the data sheet from https://pdf1.alldatasheet.com/datasheet ... AJ-15.html and I made myself a little probe tied to ground.

20220415_184551.jpg
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By shorting the data out pin (pin 14) to ground, I can see if anything changes on the running memory test.

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Sure enough, on the 6th chip in the first column...

20220415_184757.jpg
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OK! we have our culprit! I reflowed the solder on it just in case. No joy.

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socket installed.

20220415_192810.jpg
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Luckily I had a spare compatible chip from a system I had pulled the RAM from to install one of Exxos' under the PSU 4MB RAM expansions. I popped it in.


Fingers crossed. Time to try a boot.

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20220415_192854.jpg
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Looking very promising!

20220415_204108.jpg
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I'm going to call that success!
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exxos
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Re: Rescuing an Ebay "for parts or spares" 520STFM board

Post by exxos »

:bravo: :goodpost:


I did a video on locating RAM chips on my TY channel. Nobody likes me though, it's fine :lol:


But in the case of that series board : https://www.exxosforum.co.uk/forum/viewt ... f=31&t=100 1040ST_Schematic_12-26-1987 C070787

It tells you bit per chip ;)

Actually I sectioned that off in a new image *somewhere* on the forum :shrug:
https://www.exxosforum.co.uk/atari/ All my hardware guides - mods - games - STOS
https://www.exxosforum.co.uk/atari/store2/ - All my hardware mods for sale - Please help support by making a purchase.
viewtopic.php?f=17&t=1585 Have you done the Mandatory Fixes ?
Just because a lot of people agree on something, doesn't make it a fact. ~exxos ~
People should find solutions to problems, not find problems with solutions.
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Badwolf
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Re: Rescuing an Ebay "for parts or spares" 520STFM board

Post by Badwolf »

Another one resurrected!

Something something Easter something

Great work! :)

BW
DFB1 Open source 50MHz 030 and TT-RAM accelerator for the Falcon
DSTB1 Open source 16Mhz 68k and AltRAM accelerator for the ST
Smalliermouse ST-optimised USB mouse adapter based on SmallyMouse2
FrontBench The Frontier: Elite 2 intro as a benchmark
Elethiomel
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Re: Rescuing an Ebay "for parts or spares" 520STFM board

Post by Elethiomel »

Thanks guys!

exxos wrote: Thu Apr 28, 2022 11:17 pm :bravo: :goodpost:

I did a video on locating RAM chips on my TY channel. Nobody likes me though, its fine :lol:

But in the case of that series board : https://www.exxosforum.co.uk/forum/viewt ... f=31&t=100 1040ST_Schematic_12-26-1987 C070787
Aww, I like you :D Got a link to the channel? I felt like experimenting a bit by using my probe so no cheating and using schematics :D

This board will appear soon in Ebay Board 2 : The mystery of the failed 6 to 2 chip TOS upgrade. STAY TUNED!
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Re: Rescuing an Ebay "for parts or spares" 520STFM board

Post by exxos »

Elethiomel wrote: Thu Apr 28, 2022 11:30 pm Aww, I like you :D Got a link to the channel? I felt like experimenting a bit by using my probe so no cheating and using schematics :D
https://www.youtube.com/user/exxosuk/videos

Must be this video I was waffling on about it in



Elethiomel wrote: Thu Apr 28, 2022 11:30 pm This board will appear soon in Ebay Board 2 : The mystery of the failed 6 to 2 chip TOS upgrade. STAY TUNED!
Cool!
https://www.exxosforum.co.uk/atari/ All my hardware guides - mods - games - STOS
https://www.exxosforum.co.uk/atari/store2/ - All my hardware mods for sale - Please help support by making a purchase.
viewtopic.php?f=17&t=1585 Have you done the Mandatory Fixes ?
Just because a lot of people agree on something, doesn't make it a fact. ~exxos ~
People should find solutions to problems, not find problems with solutions.
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derkom
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Re: Rescuing an Ebay "for parts or spares" 520STFM board

Post by derkom »

exxos wrote: Thu Apr 28, 2022 11:17 pm I did a video on locating RAM chips on my TY channel. Nobody likes me though, it's fine :lol:
Being liked and being right are orthogonal.
russellnash
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Re: Rescuing an Ebay "for parts or spares" 520STFM board

Post by russellnash »

Useful information, thanks. I started looking again at several boards that have RAM problems primarily just to get experience for when my currently working STs start playing up. I have a question to RAM diagnostics using the cartridge. Maybe I am missing something here or am just plain stupid but in this example if you read from left right the fault displayed is bit 5. That seems very straight forward. However in the following example

https://www.exxosforum.co.uk/forum/viewt ... &start=220

the output is read from right to left, showing bits 8 and 10 as the error. Should the output be read from left to right or right to left?
zChris
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Re: Rescuing an Ebay "for parts or spares" 520STFM board

Post by zChris »

Very nice and educational! Thanks!
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exxos
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Re: Rescuing an Ebay "for parts or spares" 520STFM board

Post by exxos »

russellnash wrote: Fri Apr 29, 2022 11:36 am the output is read from right to left, showing bits 8 and 10 as the error. Should the output be read from left to right or right to left?
Explained here https://www.exxosforum.co.uk/forum/viewt ... 143#p47751
https://www.exxosforum.co.uk/atari/ All my hardware guides - mods - games - STOS
https://www.exxosforum.co.uk/atari/store2/ - All my hardware mods for sale - Please help support by making a purchase.
viewtopic.php?f=17&t=1585 Have you done the Mandatory Fixes ?
Just because a lot of people agree on something, doesn't make it a fact. ~exxos ~
People should find solutions to problems, not find problems with solutions.
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