TS1500 no video

Discussions about Sinclair ZX80 and ZX81 Hardware
computergui
Posts: 15
Joined: Tue Mar 09, 2021 10:56 pm

Re: TS1500 no video

Post by computergui »

Update!

Making progress, I think. I replaced all the power related diodes, and socketed the memory chips. Still no video. I tested the ROM in my 1500, and it worked fine. Good news! I also tested the Z80 on my 1500 and got a black screen. Hmm...maybe bad Z80.

I tried my working Z80 in the bad machine...nothing. I tried an older Z80 that i have from a TS1000 and I noticed we go voltage on R20. Plugged up the composite mod and we got video!! But, only a nice and bright white screen. No K cursor :( Added a 16K Ram pack. Same.

How sensitive is the 1500 to a specific Z80?

Memory chips were tested and voltage is within range. Logic probe arrives tomorrow and I have my eye on an ossciliscope!

Don
Timex Sinclair 1000
Timex Sinclair 1500
Timex Sinclair 2068
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bola_dor
Posts: 259
Joined: Wed Oct 02, 2019 5:32 am

Re: TS1500 no video

Post by bola_dor »

A white screen means the the ULA is working.. and that's very good news for a 1500 as is the only one part you can't replace this days!!!..
Z80 from a TS1000 should be the same.
If ICs were ruled out. Check all data and address lines. Pin by pin . Have in mind that some lines have resistors in them so continuity will fail if tested directly. (Check from the spected resistence) it is better if you test from the IC pins as that will rule out a miss contact too.
Rampack disconnect internal ram on ZX81 and TS1000 but I think it is no the same on TS1500.. so you can still have ram problems.. I guess..
Last edited by bola_dor on Sat Mar 20, 2021 10:12 pm, edited 1 time in total.
Ernesto
ZX80, TK83, CZ1000, CZ1500, TK85, CZ2000, CZ1000Plus, CZ Spectrum, TK90X 16Kb, CZ Spectrum Plus, TS2068, Sinclair QL. TS 1016, TS1040. And more to come :D
Spinnetti
Posts: 88
Joined: Sat Sep 12, 2020 11:29 pm

Re: TS1500 no video

Post by Spinnetti »

Great, so with a good ula, should be able to fix about anything else I would think. Practically everything else is already replaced - matter of elimination! lol
Sinclair AM mini radio
TS1000/Composite Mod
TS1500/Composite Mod
TS2068
Spectrum 48k/Composite Mod
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Interface 1 & Microdrives
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computergui
Posts: 15
Joined: Tue Mar 09, 2021 10:56 pm

Re: TS1500 no video

Post by computergui »

So, I'm in the the process of tracing data and address lines.

I notice they run through 2 separate ICU's. 74LS244 and 74LS245 data buffers. How often do these things fail? I haven't traced them yet, but I'm curious.
Timex Sinclair 1000
Timex Sinclair 1500
Timex Sinclair 2068
ZX Spectrum 48K
ZX Spectrum Plus
Sinclair QL
computergui
Posts: 15
Joined: Tue Mar 09, 2021 10:56 pm

Re: TS1500 no video

Post by computergui »

computergui wrote: Wed Mar 24, 2021 8:40 pm So, I'm in the the process of tracing data and address lines.

I notice they run through 2 separate ICU's. 74LS244 and 74LS245 data buffers. How often do these things fail? I haven't traced them yet, but I'm curious.
And even with good continuity from the pins, if the ICS are bad, I assume the machine wouldn't boot to the cursor.
Timex Sinclair 1000
Timex Sinclair 1500
Timex Sinclair 2068
ZX Spectrum 48K
ZX Spectrum Plus
Sinclair QL
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1024MAK
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Location: Looking forward to summer in Somerset, UK...

Re: TS1500 no video

Post by 1024MAK »

74LS244 and 74LS245 data buffers are normally reliable, but just like anything else, they can fail.

Mark
computergui
Posts: 15
Joined: Tue Mar 09, 2021 10:56 pm

Re: TS1500 no video

Post by computergui »

1024MAK wrote: Wed Mar 24, 2021 9:12 pm 74LS244 and 74LS245 data buffers are normally reliable, but just like anything else, they can fail.

Mark
I've ordered a few and should have them in a couple days. I'll let you know.
Timex Sinclair 1000
Timex Sinclair 1500
Timex Sinclair 2068
ZX Spectrum 48K
ZX Spectrum Plus
Sinclair QL
dessony
Posts: 302
Joined: Tue Oct 29, 2013 2:26 pm
Location: Indiana, USA

Re: TS1500 no video

Post by dessony »

https://www.electronicsrepairmadeasy.co ... ester.html

This website abovementioned can test the TS1500/ZX Spectrum 16/48's inductors. I am trying to help all of you.

Cheers,
DesSony
Spinnetti
Posts: 88
Joined: Sat Sep 12, 2020 11:29 pm

Re: TS1500 no video

Post by Spinnetti »

Thanks. Eventually we will have replaced every chip lol...
Sinclair AM mini radio
TS1000/Composite Mod
TS1500/Composite Mod
TS2068
Spectrum 48k/Composite Mod
Spectrum+
Interface 1 & Microdrives
Speccy Vdrive
QL/Minerva w/TKII/Custom PSU/QL-VGA
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