Another repair case, plase help if you can

[laios]

Hi sorry for the long delay but several problems keep me away from this
today I completed the check also I replaced the tms9929anl
not any progress except I had only one screen like the one in photo but this time blue background
that happened only once all other times black screen and now I have continuous tone
there is one rom the first from top with a sticker "Spain" (that mtx was from Spain ,indeed)
that rom is piggyback and soldered over another one and I think that goes somehow warm ,is there a way to replace the roms ?
can the problem be there ?
until now cpu , ram , video ram , video processor, are replaced with new

[Martin A]

The roms can be replaced, but it might require surgery. MTX's came out of the factory with either production ROMS, or they had EPROMS fitted.

Unfortunately the EPROMS Memotech used were 25 series devices from TI and they have a different pin out to the modern 27 series EPROM (and 28xxx EEPROM) and the mask roms were different again.

The Circuit diagrams in the manual, of the -04 motherboard, show a number of alterable links which might make fitting an EPROM or EEPROM possible but would need soldering as they're made with wire, and not jumpers and shunts.

My MTX is an -05 and that has no links, and came out of the factory with cut tracks and patch wires to fit EPROMS, (it's since had more cuts and new patch wiring as I have 2864's on-board now instead of 2564's but that's another, long, story). From the photo's on Dave's site the -06 board has no links either.

Another way without resorting to surgery on the MTX would be to build a small adaptor board to plug an EPROM into the on-board socket. That might have clearance issues with the keyboard, and exactly what signals need changing depends on the original ROMS are.

[laios]

this one is a -05 too

[Martin A]

MTX1A and MTX1C are mask roms, I'd be very surprised if they were the cause of the problem.

The SPAIN chip where it's soldered to MTX1B ROM on the other hand could be, but I've never know a mask rom go bad, but solder joint are another matter....

The flying lead connects the chip select of the Spain rom to the GROM signal on the expansion connector, so that the language chip appears as ROM 7. Make sure that the rom end isn't touching the chip select of 1B underneath

(Incidentally,don't try NODE ROM or Magrom on that system as they both respond as ROM 7 and would most likely clash)

The pin out for those sockets is

Code: Select all

5v  o      o 5v
0v  o      o (LK13)
A7  o     o 5v
A6  o     o A8
A5  o     o A9
A4  o     o A12
A3  o     o chip select
A2  o     o A10
A1  o     o A11
A0  o     o D7
D0  o     o D6
D1  o     o D5
D2  o     o D4
0v  o     o D3

The circuit diagram doesn't give a default for Lk13 on the 05 board, I've a vague feeling it might be 0V

compare that to what an 8k eprom would need in system,

Code: Select all

5v  o      o 5v
A12 o      o 5v
A7  o     o no connect
A6  o     o A8
A5  o     o A9
A4  o     o A11
A3  o     o output enable
A2  o     o A10
A1  o     o chip select
A0  o     o D7
D0  o     o D6
D1  o     o D5
D2  o     o D4
0v  o     o D3

There's quite a bit of track cutting requires, and I seem to remember one of those cuts is under the socket, and of course once it's done you would need more patch wire to go back to the mask roms. the back of my MTX's board looks like this:

patch wired for 27C64 or 28C64B.jpg (99.61 KiB) Viewed 9128 times

An adapter socket for MTX1B might be worth trying ( I believe that's the "basic" rom),

[1024MAK]

MTX ROM/EPROM pin-out info here

Mark

[laios]

many thanks for all the info you provided all of you , although little hard to follow as I'm not familiar with Eproms
but I'll study several times your info and hope at least to learn something
for now I can confirm that the "Spain" chip select does not touch the underneath rom pin
I have a pic of the under side with the wired routes and one question : will be worth to desolder the "Spain" rom ?

[1024MAK]

... and one question : will be worth to desolder the "Spain" rom ?

No.

I would not rush to judgement on the ROMs. Mask ROM chips are normally fairly reliable. And unless you can program EPROMs (or EEPROMs) and you cut tracks and rewire the pins that are different, they are not easy to replace. Unless you happen to have another MTX board with the exact same type of ROMs.

If you can program EPROMs (or EEPROMs) it would be worthwhile programming a chip with Andy Key's "test card" program. This makes no use of RAM, it only uses the Z80 CPU, the address, control and data bus, the VDP (and it's RAM). If it works, it gives a good indication that the main part of the board works.

Mark

[laios]

I have a friend with an Willem programmer he can help me with the eproms
from what I saw from the photos it is more easy to cut the track and solder the wires than all 16 Ic sockets I soldered so far
so I give it a try ,from what I saw only 1 track cut on ROM 1B and rest wired from under side right ?
where I can found Andy's test ROM ?

[Crazyboss]

http://www.nyangau.org/memotech/testcard.zip

[1024MAK]

I have a friend with an Willem programmer he can help me with the eproms
from what I saw from the photos it is more easy to cut the track and solder the wires than all 16 Ic sockets I soldered so far
so I give it a try ,from what I saw only 1 track cut on ROM 1B and rest wired from under side right ?
where I can found Andy's test ROM ?

If you want help or advice on modifiying the board so it can use 27 series EPROMs, or 28 series EEPROMs, let us know.

Mark