Ferranti ULA 5C114E info?

[RobG]

Hey @bola_dor, I have a Spectrum with 5C11E ULA, which appears to be bad. I am not sure if someone was trying to convert PAL Spectrum to NTSC Spectrum or if this thing is original (it looks original.) If you are willing to sell one or two of your ULAs, I could try to make it work and if it does, I could post everything about that particular ZX.

[bola_dor]

Hey @bola_dor, I have a Spectrum with 5C11E ULA, which appears to be bad. I am not sure if someone was trying to convert PAL Spectrum to NTSC Spectrum or if this thing is original (it looks original.) If you are willing to sell one or two of your ULAs, I could try to make it work and if it does, I could post everything about that particular ZX.

So you never saw it working?
What are the crystals frequencies?
I answered your PM

[RobG]

Test ROM reports bad RAM and possibly ULA and multiplexer chips. I would prefer to eliminate ULA as a suspect before I start replacing other chips.

EDIT: after more testing, it turns out the PS is bad. ULA is good, woot, woot!

[RobG]

Fixed the power supply and everything works, however, the color and quality of the image is pretty bad. It could be that my new generation TV doesn't like Spectrum's signal that much or that I need to replace 14MHz crystal with 14.112 (which can be found in 2068) and make some adjustments with trim pots.
In any case, after looking closer at the PCB, it appears that the 3.57 crystal is not original, so it is possible that this is not the evasive 5C114E Spectrum. The only thing different was DC jack, which was 3.5mm center positive. The jack looks like EAR and MIC and has the same residue, so I am assuming it was original (I replaced it with 2.1mm barrel.)

EDIT: pictures below are from my Sony LCD TV, which may not work well with Spectrum to begin with.

[bola_dor]

Fixed the power supply and everything works, however, the color and quality of the image is pretty bad. It could be that my new generation TV doesn't like Spectrum's signal that much or that I need to replace 14MHz crystal with 14.112 (which can be found in 2068) and make some adjustments with trim pots.
In any case, after looking closer at the PCB, it appears that the 3.57 crystal is not original, so it is possible that this is not the evasive 5C114E Spectrum. The only thing different was DC jack, which was 3.5mm center positive. The jack looks like EAR and MIC and has the same residue, so I am assuming it was original (I replaced it with 2.1mm barrel.)

IMG_9603.jpgIMG_9602.jpgIMG_9604.jpgIMG_9606.jpgIMG_9607.jpg

Thats are good news.. much of the moire in the pictures is added by the cellphone camera.. you should spectrum some pixel crawling in a modern display.. an ISSUE 2 with original electrolytics wont help on noise . Are the mods to the 12v supply already done?
And look for the ceramic capacitors replacement over the low ram 12v line..
I don't know what issue board wasbused by chilean NTSC version but I susoect it was a later one.. argentinian CZ2000 used ISSUE6A boards...

[RobG]

Yes, moire pattern is caused by the phone. Power supply has the simple mod and I will replace all caps later on. I may also swap 14MHz crystal with the one from 2068 just to see if there's any improvement.

[1024MAK]

There are a number of recommended modifications for issue 2 boards.

Improvements to the DC-DC converter circuitry is one, see this link.

For some of the other modifications, see also this web page.

It’s also well worth reading through the service manual.

Mark

[RobG]

Replaced 14.000MHz crystal with 14.112MHz, added 51R resistor on the output (to get rid of reflection,) replaced C25 and C65, made some color adjustments, and here are the results:

Still not perfect, but my LCD monitor could be the problem here. Picture on my large screen TV is better than it was, but still a mess, so I will not use it for testing anymore.
I will replace the remaining caps and see if there's any further improvement.

BTW, which memory bypass caps were problematic, the glass ones or the black ones?

[bola_dor]

BTW, which memory bypass caps were problematic, the glass ones or the black ones?

See here https://spectrumforeveryone.com/technic ... -spectrum/

[1024MAK]

BTW, which memory bypass caps were problematic, the glass ones or the black ones?

In terms of reducing the visible artefacts that are often referred to as jail bars, it’s not that the capacitors fitted are defective. It’s more along the lines that people expect a much better picture on their higher resolution TVs today compared to in the 1980s when most home computers were being used with 14” CRT TVs.

Hence to improve the picture, replace C5 to C8. These decouple the +12V supply to the 4116 (or equivalent) DRAM chips (they actually run off the +12V supply, not the +5V supply). Sinclair used the smallest possible value to keep costs low. I recommend 470nF or 1uF multilayer ceramic capacitors.

If your board has disc ceramic capacitors, Sinclair recommends these are replaced with axial types. However, if the existing capacitors are physically okay, and works okay, then it’s okay to leave them alone.

Mark