TS1500 problems when using a ZX8-CCP

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JackTheKnife
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TS1500 problems when using a ZX8-CCP

Post by JackTheKnife »

HI all. I have ended up here as I have decided to put ZX8-CCD board into Timex 1500 (US version of ZX81). Before I have transistor mod taken from my Atari 2600 but it had "jail bars" so I had hope that ZX8-CCD board will produce better outcome.

After installation I have got whole white screen, no cursor. I have found few posts, on this forum, that default sync for ULA may not be the same as installed and will require some adjustments on R1. After getting cursor on the screen I have power down and power up to see if that will work but it will work like twice or 3 times on 10 power cycles. Jail bars, when the cursor is up, are still there but not that much noticeable.

I have found one page talking about ZX8-CCD board in Timex 1000 (ZX80), that it still will require some transistor mod to get it to work. On another hand I have found posts that logical AND/OR may not work on IC correctly (faulty chip installed?). At that point my question is if any of those statements are correct for my case and if how to get it fix it?

Thanks
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1024MAK
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Re: TS1500 problems when using a ZX8-CCP

Post by 1024MAK »

A few pointers:
  • First, the ULA in a TS1500 will have a slightly different output to the ULA chips used in ZX81 / TS1000 machines, so yes, the ZX8-CCP will probably need adjusting.
  • Second, there are two adjustments - read Pokemon’s set-up instructions (should have been supplied with the ZX8-CCP). Careful adjustable is needed, as there is an interaction between the adjustments.
  • Third, I think the TS1500 ULA already generates the back porch part of the video signal, so keep in mind that the ZX8-CCP also generates a back porch, or a longer than normal one if the video signal already includes one. Some TVs don’t like this.
  • Fourth, jail bars are often caused by a lack of decoupling on the power supply lines feeding the DRAM chips. Insufficient decoupling means when a digital chip changes its output, there is a slight drop in the voltage on the power rails, the symptoms of this can be seen as interference on the video picture. If you are good at soldering, add four 470nF or 1uF multilayer ceramic capacitors between the +12V supply and the 0V/GND rail as near as possible to the relevant pins of the 4116 DRAM chips (one per pair of 4116 chips, evenly spread between the eight DRAM chips). These can replace any existing smaller value capacitors. It would also be wise to renew any electrolytic capacitors associated with the +5V, +12V and -5V supply rails and associated power supply circuitry. Low ESR types would be best, but are not essential.
Mark
JackTheKnife
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Re: TS1500 problems when using a ZX8-CCP

Post by JackTheKnife »

Thanks for quick replay.

Regarding #1 and #2 - I have did what was described in the Pokemon’s set-up instructions - "zeroed" both resistors and then started with R1 to find correct sync signal then trying to adjust R2 but that one didn't do anything noticeable except making cursor whole black block on a white screen.

Re #3 - I didn't know about it. Sounds like I need to read more :)

Re #4 - sounds like a right way to go. I think I will re-cap first and see if that will fix "jail bars" if not then will go with adding capacitors to the DRAM. Just one question - are there any examples (or photos) how to get done (where to solder) for the second part?
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1024MAK
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Re: TS1500 problems when using a ZX8-CCP

Post by 1024MAK »

Unfortunately TS1500 machines are not very common on this side of the Atlantic (Europe) which makes giving help and advice more awkward. There is a schematic for one version of the TS1500 available on line, but not of any other version (there are at least two different board revisions/versions).
Good quality photos of the boards are also harder to find.

If you can you take a good quality photo of your board, and post it here (please compress it as a ZIP file) that would help. Use if using a camera that has a macro mode, see if using this helps with the focus. As I need to be able to see the fine details.

Mark
Lardo Boffin
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Re: TS1500 problems when using a ZX8-CCP

Post by Lardo Boffin »

I have a TS1500 (which I had to ship from America to the UK) but I wimped out and got Mutant Caterpillar Games to fit a ZXVid (https://www.sinclairzxworld.com/viewtop ... 879#p26879) which does a fantastic job on the display as i believe it is ‘auto adjusting‘ or at the least rarely needs adjusting (it also cost quite a lot more).
Given the cost of the 1500 in the first place I was more than happy to spend the money and not risk me botching it!
ZX80
ZX81 iss 1 (bugged ROM, kludge fix, normal, rebuilt)
Iss 3 ZXVid
TS 1000 iss 3, ZXPand AY, ZX8-CCB, ZX-KDLX & ChromaSCART
TS 1500 & 2000
Spectrum 16k (iss 1 s/n 862)
Spectrum 48ks plus a DIVMMC future and SPECTRA
Spectrum +2a
JackTheKnife
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Re: TS1500 problems when using a ZX8-CCP

Post by JackTheKnife »

This is how "jail bars" were looking as when transistor mod was used:
2018-03-17 19.55.25.jpg
and here when ZX8-CCD used:
2020-09-11 10.41.34.jpg
Also attached high res photos of the board:
TS1500 board.zip
(4.44 MiB) Downloaded 19 times
bola_dor
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Re: TS1500 problems when using a ZX8-CCP

Post by bola_dor »

Here you can find TS1500 schematics
viewtopic.php?f=7&t=1582#p16357
As Mark suggested you can try replacing C33, C35, C37, C39.

Here you can se how is it done with Spectrum that has similar low ram layout. https://spectrumforeveryone.com/technic ... -spectrum/

My TS1500 has a different issue board with a different ram but it had an (*)4.7uF electrolytic on the 7805 regulator output (from factory) as you can see at the bottom right corner.
20200919_094504.jpg
Also this "Mikey mouse" 104 ceramics aded may help if your PSU is noisy to..
IMG-20200823-WA0114-01.jpeg
This is a CZ1000 Plus, a TS1000 argentinian clone that had that electrolytic you can see behind (its 22uF 16v)



I think It won't hurt to try
(Edited because I mistakenly hit the send button uF value (*) has been corrected..)
ZX80, CZ1000, CZ1500, CZ2000, CZ1000Plus, CZ Spectrum, Sinclair QL.
JackTheKnife
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Re: TS1500 problems when using a ZX8-CCP

Post by JackTheKnife »

Before going with the recap is it worth to replace 7805 with Traco or other replacement which can be found on the SellMyRetro?

Other way I will go with "Mickey Mouse" and if that will not help re-cap of C33, C35, C37, C39

Thanks for the help!
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1024MAK
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Re: TS1500 problems when using a ZX8-CCP

Post by 1024MAK »

Sometimes 7805 voltage regulators become electrically noisy. And a Traco or Recom or similar good quality DC-DC converter / switching regulator will be far more efficient (Traco and Recom DC-DC converters / switching regulator run cool). So yes, it is worthwhile replacing the existing 7805.

There is a topic on here where there are photos of a ZX81 that has been fitted with a Recom DC-DC converter / switching regulator.

Mark
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