Broken interesting Spectrum

[Lardo Boffin]

I bought an interesting looking Spectrum recently but sadly it is not working too well...

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Inside the black TS1500 style case it is a standard issue 3B.

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Assembled by Timex:-

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But a bit poorly - this is the boot screen in RF.

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I may do a quick composite mod tonight so I can see the image a bit better.

As far as I can tell it is getting stuck on the initial black screen?

Any suggestions for someone with no ‘scope or logic probe? Apart from to get a ‘scope and probe...

Thanks!

Lardo

[1024MAK]

Yep.

First off, check the three supply rails, +5V, +12V and -5V. If the -5V is not within spec. (-5.5V to -4V) OR the +12V is the same as, or lower than the +9V input voltage (and/or not in spec. 12V +/- 10%) switch off and investigate TR4, TR5 and the 'coil'.

If the all the supply rails are okay, I recommend a test ROM which contains a RAM testing program. I use a diagnostic board. But there are other options.

More later...

Mark

[1024MAK]

Diagnostic ROM

Brendan has improved and expanded on some existing ideas and code for testing ZX Spectrum memory. See here.

There are some Spectrum fault finding tips in this recent thread

Mark

[1024MAK]

I bought an interesting looking Spectrum recently but sadly it is not working too well...

Yeah, Timex of Portugal made various ZX Spectrum 'models' that were sold in Portugal and Poland and some other nearby countries that were not within the area controlled by Sinclair Research Ltd.

Mark

[1024MAK]

Here is a link to a discussion on WoS forums about the Timex ZX Spectrum computers...

Mark

[Lardo Boffin]

Here is a link to a discussion on WoS forums about the Timex ZX Spectrum computers...

Mark

Interesting stuff! So having had a quick read no one actually knows what was going on?
Mine is a normal (I assume) 48K Spectrum inside a black TS1500 case.

I will give the voltages a go tomorrow. Ran out of time packing stuff to send tonight.

[1024MAK]

Oh, re-reading what I posted, I forgot to say...
If the -5V is missing or out of specification, don't leave the machine powered up for very long, as this is a required bias voltage for the 4116 DRAM chips. Without the -5V, the chips may be damaged.

And of course, sometimes a damaged 4116 DRAM chip will drag down either or both of the +12V and -5V supplies.
The 4116 DRAM chips are actually powered by the +12V, the +5V is just to Interface to the rest of the computer.

Mark

[axtelle]

Have you been here... https://beta.collectorsbridge.com/colle ... um-ts-2000

[axtelle]

I wonder could you be trying to display a PAL-N (Argentinian) signal on a PAL-I (UK) TV set ?

Here's some info on the PAL variants - https://en.wikipedia.org/wiki/PAL

[Lardo Boffin]

Thanks for the links!

I have a Spectra SCART which produces a picture by listening to RAM writes which presumably would ignore the tv output type? My only concern is that if this is just a dodgy computer it could damage my Spectra (which was rather expensive).