No video output from my TS1500

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Kahenraz
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Joined: Mon Feb 10, 2020 2:06 pm

No video output from my TS1500

Post by Kahenraz »

This is my only TS1500 so I don't have another set of chips to swap in. It never worked upon receipt.

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
mcarlson_sb
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Location: San Francisco

Re: No video output from my TS1500

Post by mcarlson_sb »

mcarlson_sb wrote: Sun Jul 19, 2020 5:24 pm I found this thread with lots of good troubleshooting advice.

And this thread

Going through them now.

I might suggest that a version of it be made sticky.
I don't have a TS1500 but I suspect the troubleshooting will be similar to the Ts1000 and Z81

Cheers,
Matthew
bola_dor
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Re: No video output from my TS1500

Post by bola_dor »

mcarlson_sb wrote: Sun Jul 26, 2020 7:23 pm
I don't have a TS1500 but I suspect the troubleshooting will be similar to the Ts1000 and Z81

Cheers,
Matthew
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
ZX80, TK83, CZ1000, CZ1500, CZ2000, CZ1000Plus, CZ Spectrum, CZ Spectrum Plus, TS2068, Sinclair QL. TS 1016, TS1040.
Kahenraz
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Joined: Mon Feb 10, 2020 2:06 pm

Re: No video output from my TS1500

Post by Kahenraz »

There is no video output at all. I tried switching channels but the TV remains blue (no signal). The display from my TS1000 units work fine on this TV.
mcarlson_sb
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Location: San Francisco

Re: No video output from my TS1500

Post by mcarlson_sb »

It's going to be harder to diagnose a signal problem without an oscilloscope. The switching happens faster than a multimeter can give results (or a human could read them)

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.
Kahenraz
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Re: No video output from my TS1500

Post by Kahenraz »

I ordered an inexpensive oscilloscope from eBay along with some leads and a function generator for testing.

https://www.ebay.com/itm/203047787848

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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1024MAK
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Re: No video output from my TS1500

Post by 1024MAK »

Unfortunately the oscilloscope you have linked to is only really useful when working with audio signals. Audio signals are considered to be in the range 50Hz to 20kHz. The signals inside even an inexpensive computer like a ZX81/TS1000 or TS1500 run at 1MHz to 3.5MHz. Frequency is the rate of change of AC or pulsed DC signals. It used to be measured in cycles per second before the powers that be decided to honour Herz by naming it after him (see here).

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.

Mark
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Ed in SoDak
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Re: No video output from my TS1500

Post by Ed in SoDak »

Der, whoops. Before reading the replies here, I replied to the thread with pics you linked to above. The gist of my post was to try an external RAM pack, since the 1500 will remap internal memory and use the pack as primary "boot" RAM. Still no go, then you likely have problems unrelated to RAM. If you have a CRT TV, that will be easiest to start with for checking operation, being more of a sure thing. Or if you have an old VCR, feed the 1500 into it and connect the VCR on to your LED monitor. Getting any kind of image other than blue screen will help troubleshoot.

Having a 1500 here that also took some work to get going, I'll chime in if I can help further.
-Ed
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mrtinb
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Re: No video output from my TS1500

Post by mrtinb »

It would be wise to tell which type of TV you have.

Never TVs might not show a picture, even if the computer is working.
Martin
ZX81, Lambda 8300, Commodore 64, Mac G4 Cube
Kahenraz
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Joined: Mon Feb 10, 2020 2:06 pm

Re: No video output from my TS1500

Post by Kahenraz »

I've been meaning to add a quality oscilloscope to my workbench for a while now. My research suggests that an entry level Rigol DS1054Z is a good unit.

Would this be sufficient for any diagnostics I would need to do on a TS1500?

What would I need for logic probes?
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