Where to find GLUE and MMU chip ?

[San-A]

Hi,
I have a 1040 STF with a white screen.
- Motherboard is C070523-001 Rev D
- Power led is on
- Floppy is running with the led on
- PSU voltages are ok
- Diag card displays nothing.
Following the Service Manual it could be the GLUE, MMU, CPU, clock.
After investigation I can see that a pin of the GLUE seems oxydized. So it could be the problem or not. Anyway I am looking for chips to test.

Unfortunatly GLUE (C025915-38A), MMU (C025912-38) are no longer availlable at the EXXOS Store.
Do you have any idea where I can buy them ?
Moreover is there a difference between GLUE 38 and 38A ?

Thanks
San-A

[exxos]

Time permitting I may have some more chips in stock soon.

[San-A]

Good news (again)
Keep me in touch as I want also buy the ubeswitch mk6.

[rubber_jonnie]

White screen in my recent experience, with nothing from the diag card, is very possibly ROM related, and this was the case on my Mega 4. The problem was a bad ground on one of the ROM chips.

Incidentally, have you tried connecting a serial cable to the ST and a PC running Hyperterm at the other end? You may get some diag data at the PC terminal, you may not, but it is worth trying.

Check all the ROMs have 5v and a good GND, and that all the address and data lines are good. A logic probe is a good place to start, and you can also use a multimeter in continuity test mode to buzz out the lines.

I'd also suggest this: https://www.exxosforum.co.uk/forum/viewt ... hilit=plcc

And at the same time, clean the socket contacts with DeOxit or Electrolube followed by the chip contacts before reinserting.

Whilst I've had a few GLUE chips die of late, I haven't had any MMUs go. Not to say they don't, but be sure to check all other avenues before replacing the chips. Probably the simplest method of getting chips for testing is to get another ST :)

Trouble is that is getting expensive these days.

Also worthwhile checking the HALT status on the CPU, which is active low. It's bi-directional, meaning that either the CPU or ST can call HALT, but if it is low during boot, it is possible the CPU is getting junk and halting, which was the problem on my Mega, as the LO1 ROM had no ground. You can use a multi-meter to check if it's 5v or 0v.

Also worthwhile testing is the RESET line, which is also active low. You can test this with a multi-meter too. With power on press and hold reset, the reset line should drop to 0v, then jump up to 5v quickly when you release. It's easier to see on a scope, but you can see it on a multi-meter.

A logic probe is good for seeing the transitions on these pins too, and is a relatively cheap tool for the information it can provide.

[exxos]

Keep me in touch as I want also buy the ubeswitch mk6.

Some now in my store.

[San-A]

Your stock has just decreased 😊

[San-A]

White screen in my recent experience, with nothing from the diag card, is very possibly ROM related, and this was the case on my Mega 4. The problem was a bad ground on one of the ROM chips.

Incidentally, have you tried connecting a serial cable to the ST and a PC running Hyperterm at the other end? You may get some diag data at the PC terminal, you may not, but it is worth trying.

Yes I have tested with a diagnostic cartridge. Nothing appears on my with Teraterm. To be sure I did the same test with my STE and that works on the PC.
I have also clean the contact with a product like Kontakt 60.
I will have a look on the link you mentioned and test the rom.

[Tomswork]

Is it a white screen complete or a white screen in frame of some other color

Tom

[San-A]

Is it a white screen complete or a white screen in frame of some other color

Tom

This is what I see on a NEC 1970nxp

0DF595CE-E0FA-4714-B3BA-6C70BF98B5D2.jpeg

[San-A]

Check all the ROMs have 5v and a good GND, and that all the address and data lines are good. A logic probe is a good place to start, and you can also use a multimeter in continuity test mode to buzz out the lines.

Also worthwhile checking the HALT status on the CPU, which is active low. It's bi-directional, meaning that either the CPU or ST can call HALT, but if it is low during boot, it is possible the CPU is getting junk and halting, which was the problem on my Mega, as the LO1 ROM had no ground. You can use a multi-meter to check if it's 5v or 0v.

Also worthwhile testing is the RESET line, which is also active low. You can test this with a multi-meter too. With power on press and hold reset, the reset line should drop to 0v, then jump up to 5v quickly when you release. It's easier to see on a scope, but you can see it on a multi-meter.

ROM 5v is ok
HALT is 5v
RESET is 5v and 0v after a reset.