Yellow screen

[98bishopmal]

Ok

So black is blackish
Blue is a very dark green
Red is fine
Magenta is a little lighter red
Green is bright green
Cyan is bright green
Yellow is yellow
White is also yellow

I have replaced tr9 and tr8 from a donor bored and still the same and have also now replaced tr1 and tr2 still the same

[1024MAK]

Time to change the ULA.

Mark

[98bishopmal]

Thanks mark

Is it worth change x1 and x2 as well or will this not help?

[98bishopmal]

Also where can I get a replacement?

[Sol_HSA]

Also where can I get a replacement?

Unfortunately, from another speccy. There are modern reproductions, though, but then you're getting into the whole Theseus's ship thing.

[98bishopmal]

Thanks Mark,

Managed to find one on eBay will let you know how it goes

[1024MAK]

Is it worth change x1 and x2 as well or will this not help?

I don’t think that will help.
If X1 was faulty, you would not get any stable screen display.
If X2 was faulty, as in not working at all, you would be no colours at all, just a monochrome picture. And if it was slightly off frequency, all the colours would be wrong.

It’s the analogue outputs from the ULA that control IC14. But this chip is normally fairly reliable.

Mark

[spider]

Regarding replacement (original types not 'modern replacements') see:

Here , please scroll down to the " What ULA works in what machine ? " section

and also Here


As I see it, in a brief sentence, as per the first link)

... The 6C001E-7 ULA is backwards compatible with every 48K machine from the Issue 1 right up to the Issue 6A ...

[Sol_HSA]

..and the modern replacement that is apparently the currently recommended one.

[1024MAK]

Regarding replacement (original types not 'modern replacements') see:

Here , please scroll down to the " What
As I see it, in a brief sentence, as per the first link)

... The 6C001E-7 ULA is backwards compatible with every 48K machine from the Issue 1 right up to the Issue 6A ...

Each ULA version can be used in the board issue it was intended for and any earlier issue boards. In other words, it’s backwards compatible with earlier boards.

The 5C102E ULAs were used in issue one and some issue two boards. The ‘dead cockroach’ daughter board is required. The transistor ‘spider’ should also have been fitted, but at the time the problem that this fixes had not been discovered.

The 5C112E ULAs were used in most issue two boards. The ‘dead cockroach’ daughter board was no longer required, the design of the ULA having been modified. The transistor ‘spider’ was however required.

The 6C001E-5 ULAs were used on some late issue two boards. The transistor ‘spider’ was however still required. May also be found in some issue three boards.

The 6C001E-6 ULAs were used on issue three boards. An additional transistor ‘spider’ was no longer required on issue three and later boards, as it became a permanent part of the PCB circuitry. This ULA version may also be found on some issue two boards. All issue two boards still need the ‘spider’.

The 6C001E-7 ULAs were used on issue four and later boards. An earlier ULA version is likely to cause unreliable operation in issue four and later boards due to a design change with both the ULA and the circuitry on the boards. However the 6C001E-7 is still backwards compatible with earlier boards.

Mark