TS1000 upgrade – log entry 1

#retrocomputing has been taking up more of my attention recently. Specifically, I found this series about refurbishing and upgrading a Sinclair ZX81. Since the Timex Sinclair 1000 is essentially a ZX81 that jumped the pond (and doubled it’s native RAM in the process), I’ve got one. And it’s been sitting in a box for 20ish…

Entries in this series:

2022, 12 , 14

#ret­ro­com­put­ing has been tak­ing up more of my atten­tion recently. Spe­cific­ally, I found this series about refur­bish­ing and upgrad­ing a Sin­clair ZX81. Since the Timex Sin­clair 1000 is essen­tially a ZX81 that jumped the pond (and doubled it’s nat­ive RAM in the pro­cess), I’ve got one. And it’s been sit­ting in a box for 20ish years, used heav­ily pre­vi­ous to that.

Time to rec­ti­fy (ha!) that situation.

After remov­ing it from the case, and admir­ing how clean it is after all this time — the capa­cit­ors look great!! — I’ve determ­ined that there are four things that need work, maybe five. Ok, maybe six. Also some sources for inspir­a­tion / reference:

  • Con­vert video out­put to Com­pos­ite – so I can see what the heck is going on. Found this source some­what loc­ally – well, it’s with­in Canada and only a few provinces over, so that’s local.
  • Upgrade the power con­vert­er – so it runs cool­er and doesn’t need that big honkin’ sheet of alu­min­um to dis­sip­ate waste heat.
  • Expand the onboard memory – a very simple upgrade that will elim­in­ate the true ‘vin­tage’ exper­i­ence of hav­ing your ongo­ing work lost due to a minor wobble while enter­ing code.
  • Upgrade the CPU to a lower power ver­sion – lower power use keeps things run­ning cool­er, and mod­ern pro­duc­tion meth­ods may mean it’ll last anoth­er 40 years? Since the cur­rent CPU is sock­eted, this is a simple chip swap. Or maybe not! I’m lik­ing the bling thing so will replace the cur­rent sock­et with a gold one 😀
  • Poten­tially (heh, I slay me) replace the ULA chip if it’s bad. They’re notori­ous for run­ning hot so this is likely in the cards anyway.
  • Replace the two capa­cit­ors with new ones.

But before get­ting star­ted, I’ll need to fig­ure out if this thing is even work­ing. And since I don’t have a vin­tage TV or mon­it­or able to dis­play the RF sig­nal, I’ll have to break out my tiny new oscil­lo­scope and probe around.

After a con­ver­sa­tion with the pro­vider of the Com­pos­ite mod PCB, and review­ing one of the videos that star­ted this whole thing, I’ve opened up the little dude and star­ted probing.

And things look good! This is the out­put video sig­nal before it gets to the RF con­vert­er, so yeah, it’s alive and try­ing to show me stuff. Which means that the ULA is ok and upgrad­ing it is not a high priority.

Fur­ther pok­ing around the ULA and the CPU also gave off signs of life. Looks like we’re good.

And that’s pretty much where I’ll end this first log entry. Depend­ing on how things go with mail deliv­ery, etc, the next step will be either upgrad­ing the power con­vert­er, or installing the Com­pos­ite PCB.


  • Always ensure power is get­ting to the part you’re prob­ing. There was a bad lamp-switch installed inline on the power sup­ply cord which gave inter­mit­tent power to the sys­tem. Frus­trat­ing to have your power be there one moment, gone the next. Fix was to replace the switch. Even­tu­ally I’ll 3D print a prop­er box for it. 

    Replaced Switch. Crusty fail­ing lamp switch in the foreground.



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