Another repair case, plase help if you can

[laios]

a small observation
I just removed the "spain" rom or 1B most propely
and the cut on the track was already there
I inspect the other points that Mark mentions and all were already cut
is this correct ?
and one more question if I replace with eproms I must replace all 3 correct ?

[1024MAK]

a small observation
I just removed the "spain" rom or 1B most propely
and the cut on the track was already there
I inspect the other points that Mark mentions and all were already cut
is this correct ?

I'll have to get back to you on this... (I'm too tired to go back and work it out right now).

and one more question if I replace with eproms I must replace all 3 correct ?

Maybe. If two are okay, you only have to replace the suspect ROM. However, in practice, you may want to replace all three, as we don't know at this stage which ones are good or bad.

Mark

[Martin A]

The picture of the underside shows all 3 chip selects yellow wired. Which is odd as the "lower" one of those (which I think is the B rom ??) is following the same path as the cut track.

I suppose it's possible the board has been converted to EPROM, and then re-converted back to ROM at some point.

[laios]

Which is odd as the "lower" one of those (which I think is the B rom ??) is following the same path as the cut track.

Yes I noticed this , If I see right in your motherboard the same track is uncut but also "yellow wired" over (although the track look to have covered with solder?)

for a little more easy comparison here the three versions laios-Martin-1024MAK



EDIT
on a second look it is a cut track , sorry but had to inspect the photo more carefully ,
to proceed I buy 3 27c64 burn them and follow this wiring ?

[Martin A]

Unfortunately the photo of my board only tells half the story, there are cut tracks on the other side too. As I needed to re-position A11 from pin 20 to pin 23 and A12 from Pin 23 to pin 2. And make provision for Chip select now pin 20 to drive the output enable pin at pin 22.

The connections pins 27 and 2 and ground on my board had already been cut, which was useful as I'm pretty sure that that track is partially covered by the sockets

There's also a teen tiny link between pins 27 and 28 on all 3 eeproms that doesn't show up too well on the photo. If that link is made without the top side changes you could end up with a direct short between 5v on Pin 28 and 0v on Pin 27

[1024MAK]

You may want to instead bend out the required EPROM legs and solder wires to them. This is a lot easier than trying to cut the tracks under the sockets that run on the top (component) side of the board.

It also means that if the mask ROM chips are not causing the problem, you can plug them back in.

Mark

Edit: the "in" that was abducted by aliens has been saved from the evil empire and returned to it's proper position at the end of my last sentence .

[laios]

as I see the photo are all 3 eproms Pin 2 joined together ?
little hard to make it out from photo

pin 27 , 2 and ground (pin 14?) cut from top side tracks on all 3 eproms ?

thanks to mention the 27 to 28 join , I would never noticed this otherwise

[1024MAK]

Details of how to use a 2764 or a 27128 EPROM without track cutting in the attachment.

Mark

[laios]

That xls was great I finaly can say I figured out what I must do
only a final question what to do with the already cuted tracks , and wiring ?
leave them as is or restore them ?

[1024MAK]

That xls was great I finaly can say I figured out what I must do
only a final question what to do with the already cuted tracks , and wiring ?
leave them as is or restore them ?

If you bend pin 20 of the EPROM up and and link to pin 22 using a wire on the EPROM pins, the track cuts and wiring shown in the picture of your board should be left as they are (left alone).

You can pick up +5V from pin 28.
For the address pin wires (A11, A12), the best way is to use a meter (on continuity or a resistance range) to trace the track, then at a convenient via (through the board plated hole), solder a thin wire. The same wire can feed the first EPROM, then loop another wire to the same pin of the next EPROM, then finally to the last EPROM.

Mark