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Help bringing my 1040STf back to life

Posted: Mon Mar 04, 2019 7:29 pm
by christopher271828
Re-discovered my Atari 1040STf in a forgotten corner of a closet and want to recreate my early 90's computer experience. But, like all old thing ( including myself ), it seems she's got a few issues. After getting a Gotek and setting up FlashFloppy, I soon discovered that my 1040 was acting as a 520. From the screenshot of Sysinfo you can see bank 1 is not working.

I have removed and re-setted PLCCs ( MMU/etc. ), but no luck. I've read that perhaps bending the pins in the PLCC to improve contact might help. Has anyone seen this before or know what/where I can start checking?

Thanks ahead for any info,
Christopher

Re: Help bringing my 1040STf back to life

Posted: Mon Mar 04, 2019 8:00 pm
by PhilC
A lot can happen over the years, mostly corrosion.

If your computer was working before it was put away then its quite likely that its due to a bad connection here or there.

As you said, take out the MMU and chevk that all pins in the socket are not deformed or stuck in, then clean the socket and MMU with IPA. Leave it to dry and then reinsert the MMU carefully. Make sure you ine the pins up and push it in so that all 4 corners push in at once.

Then give it a go.

Failing that, it's not impossible it's a dry joint or corroded pcb track but that's harder to find.

Re: Help bringing my 1040STf back to life

Posted: Mon Mar 04, 2019 8:04 pm
by PhilC
Have a look at this post for info on socket pins.

viewtopic.php?f=17&t=1484&p=16092&hilit=Mmu+pins#p16092

Re: Help bringing my 1040STf back to life

Posted: Mon Aug 26, 2019 2:16 pm
by doc
Hi. Did you finaly found out the problem ?
I have A 1040STF that presents exactly the same trouble. Bank 1 has dissapeared. I cleaned all the board and the MMU but it did not change anything.
AI also wondered if Exxos 4MB Upgrade (STFM 4MB RAM EXPANSION) would permit to get 4MB Back in this case ...
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Re: Help bringing my 1040STf back to life

Posted: Mon Aug 26, 2019 2:20 pm
by Icky
doc wrote:
Mon Aug 26, 2019 2:16 pm
Hi. Did you finaly found out the problem ?
I have A 1040STF that presents exactly the same trouble. Bank 1 has dissapeared. I cleaned all the board and the MMU but it did not change anything.
AI also wondered if Exxos 4MB Upgrade (STFM 4MB RAM EXPANSION) would permit to get 4MB Back in this case.
I would recommend fault finding the current problem before putting in a 4MB expansion as you may not be fixing the underlying issue and possibly make it harder to diagnose going forward.

Re: Help bringing my 1040STf back to life

Posted: Mon Aug 26, 2019 3:36 pm
by rubber_jonnie
I'd agree with Icky, you need to fix the exisiting problem before you do anything else.

If you've tweaked the PLCC socket pins, also make sure you clean the IC pins with IPA too, or something like DeOxit.

You can use a multimeter to buzz out all the lines, I have had to do this before and found that some of the address lines required re-joining with bodge wires on the underside to make things work again. Losing a whole bank maybe that 5v or GND is missing to the chips so also worth buzzing out.

Re: Help bringing my 1040STf back to life

Posted: Mon Aug 26, 2019 6:18 pm
by DoG
I got a bank missing on one of mine Mega ST. It was a faulty ram chip (or several). So just changed it (them) and got the whole bank back. So no mmu chip is faulty. I tried the "piggy back method" but it didn't work to get the bank back.

Re: Help bringing my 1040STf back to life

Posted: Tue Aug 27, 2019 2:51 pm
by doc
Hi,

Thank you everybody for all your nice answers. Following your words, I tested all what I could on the RAM.
First of all the board is composed of 2 banks of TMM41256P-15 chips (I included a datashit here).
TMM41256P-15.jpg
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I made some measurments (with a voltmeter, i do not have a scope)

1) Without power : All electric continuity (GRN and 5V) seems ok on every pin of each chip.

2) With power : here is the voltage I measured on each pins of each chips
A8 : 2,22 volts
DIN : between 2,89 and 3,15 volts
WRITE : 5,04 volts
RAS : 3,50 volts on BANK 1 / 4,12 volts on BANK 2 (strange isn't it ?)
A0 : 2,36 volts
A2 : 1,98 volts
A1 : 1,99 volts
VCC : 5,04 volts
VSS : 0 volts
CAS : 4,42 on BANK 1 / 5,04 on BANK 2 (strange again ...)
DOUT : from 2,43 volts to 3,19 volts
A6 : 2,24 volts
A3 : 1,98 volts
A4 : 1,99 volts
A5 : 2,27 volts
A7 : 2,25 volts

3) I also measured the voltage on the following resistors I know have to deal with the memory.
tensions.jpg
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Unfortunately, I'm not good enough in electronics to find out the trouble. What I noticed is the strange voltages differencies happening on RAS and CAS pins between the 2 banks. Not sure if I can conclude that BANK 2 is out of order ... can you ?

Another idea, but not sure at all : I used to change my TOS from 1.0 to 1.4 ... Do you think this could have to deal with ?

Any help appreciated ;)
Best

Re: Help bringing my 1040STf back to life

Posted: Tue Aug 27, 2019 3:06 pm
by exxos
You can't measure these signals with a simple voltage meter. You need a scope. but it doesn't prove anything either way.

Your options are, to get the diagnostic cart and serial link to a PC to see if it gives any clues. Or unsolder the problem bank, put sockets in, and get some new DRAM chips and just replace the whole bank.

Re: Help bringing my 1040STf back to life

Posted: Tue Aug 27, 2019 4:46 pm
by doc
Perhaps i'm wrong but the measures I get would say that there is no cut tracks on the board. So in your opinion does it worth a try to your 4MB upgrade (STFM 4MB RAM EXPANSION) ...