ROMs

Discussions about Sinclair ZX80 and ZX81 Hardware
citizenfish
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Joined: Sun Apr 11, 2021 5:31 pm

ROMs

Post by citizenfish »

I’ve got an issue one board with a faulty ROM. Where do you guys get replacements from?
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XavSnap
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Re: ROMs

Post by XavSnap »

Xavier ...on the Facebook groupe : "Zx81 France"(fr)
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1024MAK
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Re: ROMs

Post by 1024MAK »

citizenfish wrote: Sun Jul 04, 2021 9:38 pm I’ve got an issue one board with a faulty ROM. Where do you guys get replacements from?
Are you after an original Sinclair ROM chip? If so, which version? There are three slightly different versions of the code, and various different chip makes, some of which can be used in modified faster computers. And of course, these ROM chips have not been made for many, many years, so you will be buying used chips.

There are also other alternatives. The cheapest (if you have a chip programmer) is a one time programmable (OTP) EPROM. Or use a windowed EPROM. Or a EEPROM. But to use a EPROM or a EEPROM, either you need to modify the PCB or bend pins and solder wires to the EPROM/EEPROM pins, or buy or make an adapter.

There is also a ready built adapter that has a EEPROM already fitted to it, and the trader that sells them in the U.K. can program it for you if you ask them.

Also if you are using the original case, keep in mind that there is not much clearance height wise for adapters…

Mark
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citizenfish
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Re: ROMs

Post by citizenfish »

I'm not too bothered about it being original as I've modded the board already with a composite mod and socketing. It is an original case, hopefully a multirom would still fit as that looks the best option. Is there a UK supplier anyone can link to or ebay the only option?
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1024MAK
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Re: ROMs

Post by 1024MAK »

ZX81 Variations
ZX81 Chip Pin-outs
ZX81 Video Transistor Buffer Amp

:!: Standby alert :!:
There are four lights!
Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb :!:
Looking forward to summer later in the year.
citizenfish
Posts: 30
Joined: Sun Apr 11, 2021 5:31 pm

Re: ROMs

Post by citizenfish »

Thanks ordered ;-)
citizenfish
Posts: 30
Joined: Sun Apr 11, 2021 5:31 pm

Re: ROMs

Post by citizenfish »

I've made a hash of removing the old rom and have broken a trace and a couple of the pads..any tips on fixing these apart from "not being cack handed"
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1024MAK
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Re: ROMs

Post by 1024MAK »

How bad? Pad broken? Through-hole plating ripped out?

Mark
ZX81 Variations
ZX81 Chip Pin-outs
ZX81 Video Transistor Buffer Amp

:!: Standby alert :!:
There are four lights!
Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb :!:
Looking forward to summer later in the year.
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BarryN
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Re: ROMs

Post by BarryN »

Post a picture of the damage. It depends. I'm sure it can be fixed one way or another but the best solution may depend on how bad the damage is.
DrVenkman
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Joined: Mon Jul 05, 2021 3:44 am

Re: ROMs

Post by DrVenkman »

Kynar 30-gauge wirewrap bodge wires can fix almost any broken trace if you know where to route the connection. Schematics or at least a working comparison board can help here. Kapton tape over top of the bodge can help if you need to keep working on the board so you don't accidentally dislodge the repair.
Last edited by DrVenkman on Thu Jul 08, 2021 3:33 am, edited 1 time in total.
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