It appeared to be like-new cosmetically and expected to be lightly used. The internals have several bodges and a lot of flux around a large chip (probably from the factory).
It's suspected to have been working at some point as the booklets it came with has a lot of notes and markings from someone working through it.
I don't know why it doesn't work and would like some help on triage and repair. I have soldering equipment but I do not have an oscilloscope.
Photos of the board can be found here:
https://www.sinclairzxworld.com/viewtop ... f=7&t=3765
I don't have a TS1500 but I suspect the troubleshooting will be similar to the Ts1000 and Z81
Yes but RAM is similar to the Spectrum 's lower RAM . So you have to check thre different voltages at 4116 ICs and the 12v rail..
I have a 1500 version with a different RAM. https://www.sinclairzxworld.com/viewtop ... f=7&t=3761
The big Square IC is the ULA that is different from ZX81/TS1000 and Clock circuit I think is different too. But initial diagnostic should be similar at least..
Do you have any video output at least?
Did you checked voltages at 7805 regulator, 4116 ram and Z80? Look for 1024MAK signature for ICs pinouts
With a scope you can check signals coming directly from the ULA and see if proper porch/sych/character values are being created and just not making it out to the TV
If there is any chance you can borrow one, it will make the process of troubleshooting much easier.
I don't think I'll need an expensive unit for basic testing. I've never used an oscilloscope before and I don't think I'll need the features of a larger unit for now.
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The oscilloscope you have linked to does not have a very good bandwidth, and will not even be able to correctly display most of the signals that we may want you to look at.
Before we go too far down a rabbit hole, the first priority is to test the various power supply voltages.
Most of the chips run off the +5V supply which comes from the 7805 voltage regulator. This in turn needs a supply voltage with the correct polarity of between about +7.5V to about +12V. Note that if you are using an original PSU, if it’s not connected to the computer, the voltage on the output can be up to about 16V.
The (4116 or equivalent) RAM chips actually need three power supply voltages. They run off the +12V supply, but also need the -5V supply to bias the internal circuitry correctly. Plus they use the +5V supply to drive their internal output circuitry so they can talk to the rest of the logic chips. If the -5V supply is missing with the positive supplies present, they have a nasty habit of self destructing
As indicated above, details of the pin-outs are in a topic linked in my signature below.
If you don’t have a reasonably quality multimeter, buy one or borrow one. Next on your shopping list should be a logic probe. Or if you have experience at building electronic projects, you can build a very cheap logic probe. If you want to do this, I will point you to the relevant topic.
Having a 1500 here that also took some work to get going, I'll chime in if I can help further.
Never TVs might not show a picture, even if the computer is working.
ZX81, Lambda 8300, Commodore 64, Mac G4 Cube
Would this be sufficient for any diagnostics I would need to do on a TS1500?
What would I need for logic probes?