Yes I see that and it is odd. Did you use a 33Mhz oscillator ?
Can you take a picture of the board ?

Horun wrote on 2022-04-02, 00:00:

Yes I see that and it is odd. Did you use a 33Mhz oscillator ?
Can you take a picture of the board ?

Yes I use a 33mhz oscillator and the cpu run at 33mhz, with 256k simm is perfect stable and pass all diagnostic test with checkit 😉

The board miss a one 8bit slot, I’am removed it because as greened by the varta.

I'm running out of ideas! Verified all, cleaned all, ecc.. tried two 256k simm and two 1mb simm on the same bank, work! But the 1mb simm is detected as 256k, if I put the two 1mb simm on the two first positions not work.

Desperately I have tried award bios from another 486 (this board have amibios), start and see 1mb of ram with four 256k simm (amibios see only 640k). But with award bios ask me the password and not see over 1mb... but can be "normal" is or another chipset! (Ali vs Opti)

Is possible a bios issue? My Amibios can be damaged? It never happened to me and I didn't think it was possible. Or not?

marmotta wrote on 2022-04-01, 23:20:

No breaks […]
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weedeewee wrote on 2022-04-01, 23:04:

is the address line a9 connected to all the sockets and the 74f244 ? ie no breaks inbetween somewhere.

No breaks

Only the first simm of each bank (0-1/1-1), the sockets 0-2/3/4 and 1-2/3/4 follow another way. I need to investigate 😉

Edit, investigated: the sockets 0-2/3/4 and 1–2/3/4 going to a resistor pack and then go to another pin of the same 74f244. No breaks

mmmh. Which pins of the 244 exactly?

Good question ! I think I would try swapping the two 74f244's just too see what happens.

Horun wrote on 2022-04-02, 22:18:

Good question ! I think I would try swapping the two 74f244's just too see what happens.

I already tried, the two 244 are not the original and I have added a socket. But all four (two old and two new) are good.

weedeewee wrote on 2022-04-02, 22:05:

marmotta wrote on 2022-04-01, 23:20:

No breaks […]
Show full quote

weedeewee wrote on 2022-04-01, 23:04:

is the address line a9 connected to all the sockets and the 74f244 ? ie no breaks inbetween somewhere.

No breaks

Only the first simm of each bank (0-1/1-1), the sockets 0-2/3/4 and 1-2/3/4 follow another way. I need to investigate 😉

Edit, investigated: the sockets 0-2/3/4 and 1–2/3/4 going to a resistor pack and then go to another pin of the same 74f244. No breaks

mmmh. Which pins of the 244 exactly?

The first simm at pin 17, the last three simm at pin 14.

marmotta wrote on 2022-04-02, 22:34:

weedeewee wrote on 2022-04-02, 22:05:

marmotta wrote on 2022-04-01, 23:20:

No breaks

Only the first simm of each bank (0-1/1-1), the sockets 0-2/3/4 and 1-2/3/4 follow another way. I need to investigate 😉

Edit, investigated: the sockets 0-2/3/4 and 1–2/3/4 going to a resistor pack and then go to another pin of the same 74f244. No breaks

mmmh. Which pins of the 244 exactly?

The first simm at pin 17, the last three simm at pin 14.

Are you sure about those pins ? since the address lines should just go to the memory, I'd expect both to be outputs on the 244, yet with the pins you say, 17 being an input and 14 being an output...
Somehow that doesn't make sense to me.

Can you test for activity on the A9 line of the different sockets of a bank ? ie oscilloscope or logic tester, preferably during the memory test

weedeewee wrote on 2022-04-02, 22:55:

Are you sure about those pins ? since the address lines should just go to the memory, I'd expect both to be outputs on the 244, […]
Show full quote

marmotta wrote on 2022-04-02, 22:34:

weedeewee wrote on 2022-04-02, 22:05:

mmmh. Which pins of the 244 exactly?

The first simm at pin 17, the last three simm at pin 14.

Are you sure about those pins ? since the address lines should just go to the memory, I'd expect both to be outputs on the 244, yet with the pins you say, 17 being an input and 14 being an output...
Somehow that doesn't make sense to me.

Can you test for activity on the A9 line of the different sockets of a bank ? ie oscilloscope or logic tester, preferably during the memory test

Sorry… I rechecked, is 6 and 14 😉

And yes, I have activity on both pins at powerup and on memory test.

6? that's also an input, though luckily, 6 is the input for the output on 14.
is pin 6 perhaps connected to U03, the big 82c495, pin 79 ?

weedeewee wrote on 2022-04-02, 23:47:

6? that's also an input, though luckily, 6 is the input for the output on 14.
is pin 6 perhaps connected to U03, the big 82c495, pin 79 ?

No, is not connected to pin79. I have some mOhm…

Oh my god! Is connected to pin 121! This in the pin 121!!!

Now go!!! Thanks for help! 😉

Cool! Glad you fixed it !
Enjoy !

hehe, congratulations!
Nice mystery tale you took us on there 😀

Good Job ! It was not quite visible in your full board picture or some one might have spotted it earlier.