Looking for ZX81 (preferably in UK) to ship to RWAP Software

[1024MAK]

Whatever you do, keep the old ULA (Ferranti ULA2C210E) as this is the later (better) type as a spare.

You can always swap the ROM chips (Motorola ZCM38818, Sinclair Research D2364C) between the two ZX81 boards. At the standard 3.5MHz speed it makes no difference. It only becomes an issue when using Andy's ULA2 in Turbo mode (that's the one available from Sell My Retro).

To use Turbo mode, you need a faster Z80 CPU.

The power socket problem could be either a poor solder joint on the PCB or more likely weak spring contacts.
Check the solder joint by using a good light (daylight is best)and carefully inspect the solder joints for cracks. Removing the old solder and resoldering it with fresh 60/40 solder is the fix (don't use the lead free type on the ZX81).
For the weak contacts, you can try to bend them slightly with a suitable flat bladed screwdriver. If this does not work, the socket will have to be renewed. There is a little bit of information on this here http://www.dataserve-retro.co.uk/contents/en-uk/d4.html

More later, go to go now...

Mark

[tdg8934]

Thanks for the info Rich. I removed the broken pieces of the flat keyboard connection pieces with a utility knife and tweezers. I don't think I'll need a new molex connector socket. Thanks.

Sounds like a pain about removing the broken keyboard membranes from the case.Ill give it a try later today. You mention soaking it in what? Soapy water or something else?

Is the ROM chip ok since the one is not Motorola for the ULA-2 installation? Do I need you to send me a good one on my next order with the ZXpand-AY board and ULA-2?

Tim

[RWAP]

OK - best send you a set of the molex connectors (as I store them in pairs) - in case the other one is also dodgy.

Soak the case top in hot soapy water - you can also try heating up the membrane with a hair dryer before removal - that can loosen the glue

In most instances, all of the glue comes away with the keyboard anyway - at least that has been my expeience.

Will need to ask Andy about the ROM chip - I didn't know the Motorola one was better for the ZX-ULA2... I have a spare ROM chip upstairs (actually it's one from a ZX80 upgrade kit...)

[tdg8934]

Thank rich. I appreciate what help and items provided but Please charge me something as you have a buisiness too. I'll need some rubber feet too as the glue doesn't stick anymore since removed on the original feet.

The ULA-2 text states that some roms won't work but Motorola ones are good. I'm not sure about the Sinclair Research roms. Please check if u would.

Tim

[tdg8934]

Mark,

I never thought about just swapping out the Motorola ROM with the Sinclair Research. Good idea!

I have a new ZXpand keyboard membrane coming so I was going to use that as a replacement for the bad keyboard membrane. I was able to remove it and the glue sheet fairly easily thanks to Riche's instructions.

I'll have a faster Z80 coming with the ULA-2 when it is ready to ship.

The power connector solder joints look good but the top metal piece is loosely making contact. Probably should be replaced but might be fixable. Can those be purchased? I'll look through the link.

Thanks,

Tim

[RWAP]

I may have a power connector - I shall check - aren't they the same as the ear and mic connectors?

[tdg8934]

They all look indentical to me.

Thanks,

Tim

[1024MAK]

I may have a power connector - I shall check - aren't they the same as the ear and mic connectors?

Yes, all three are the same type. If you have problems getting hold of them, PokeMon on this forum has found a supply (as used on his ZX80 Core - new ZX80 motherboards) that I think are the same, his post is here, the item you want is "Stück CLIFF CL1382 (3.5mm jack - exactly original like in the Sinclair ZX80)". This may of course be enough info to get one locally

Mark

[Andy Rea]

Yes i sent ULA-2, 8Mhz CPU, printed instructions (but to save weight might be better to get then online) and some kynar wire to Rwap.

Only the first 25 or so ULA-2 could only use turbo (double speed) with the faster ROM type, subsequent ULA-2 have different firmware that includes an optional wait signal, so if you have a slow ROM you can wire the wait and it will still work at double speed but insert a single ait cycle during M1 reads from ROM, or if you have the faster ROM you can leave it un-connected.

Regards Andy

[tdg8934]

Andy,

Here are my chipsets on the 2 TS1000s:

Bad keyboard/power socket computer:
1. Toshiba TMM2016P 2HE4
2. Motorola ZCM38818C 82 45
3. Zilog Z8400A PS Z80A CPU 8233
4. Ferranti ULA2C210E 8244

Good working computer:
1. NEC 22499-20B
2. Sinclair Research D2364C 649 8302P7 1981 <-- Is this a problem for the ULA-2 from RWAP Software (not Motorola)?
3. SGS Z8400AB1 Z80 ACPU 8824G-ITALY
4. Ferranti ULA20210E 8247

How do I tell from the numbers if the ROM is fast enough? I thought the motorola ones were always fast enough.

Thanks,

Tim