ZX81 with vertical hold issues?

[Lardo Boffin]

[RandUsr836]

Shame on you Moggy...

I luv what you have done to your machine, but its dirty around the Sinclair logo... I hope thats just coffee and buscuit crumbs

[Moggy]

The odd whisky spillage maybe!

No I have no time for looks as long as they do the business and this one has been pumping out a mixture of acid jazz and funk albums through the add on DAC, into my hi-fi amp since 5 o'clock and hasn't missed a beat. (pun intended.)

[XavSnap]

[Moggy]

SANY0438.jpg (29.61 KiB) Viewed 840 times

[Lardo Boffin]

This is zeddy with issues:

Compare the edge connector with a normal zeddy (dodgy one on the bottom):

Not sure I have seen many zeddies with a ‘goldie looking edge connector’!

[Moggy]

It strikes me that this one belonged to someone who knew what they were doing and had it plated somewhere.

Just noticed the issue three ULA and what looks like a date code for 1983 so last of the line for that chip.
A 1983 CPU plus a 649 ROM would make all these chips an unusual fit for an issue one board.

[Lardo Boffin]

It strikes me that this one belonged to someone who knew what they were doing and had it plated somewhere.

Just noticed the issue three ULA and what looks like a date code for 1983 so last of the line for that chip.
A 1983 CPU plus a 649 ROM would make all these chips an unusual fit for an issue one board.

A very strange board! I could do with getting edge connector on my MTX512 plated - it is terrible!

[Lardo Boffin]

I moved the ULA to another zeddy and the hold issue didn’t move with it so I guess I should be ok to refurb this one.

[1024MAK]

It strikes me that this one belonged to someone who knew what they were doing and had it plated somewhere.

Just noticed the issue three ULA and what looks like a date code for 1983 so last of the line for that chip.
A 1983 CPU plus a 649 ROM would make all these chips an unusual fit for an issue one board.

But apart from the 7805 voltage regulator, all the chips look to be 1983 parts. The modulator is also 1983.

Maybe Sinclair found a box of earlier issue one boards that had been produced with gold plated edge-connectors? Maybe originally intended for sale in a different market?

Mark