New and need help

For experts to discuss very technical stuff and newbies to ask why the Spectrum they bought off ebay doesn't work.
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New and need help

Post by Dizzy » Tue Jun 11, 2019 11:05 pm

Hi all. Need a bit of help.

Week and a half ago I bought one owner 128 +2 Grey. Quite in nice condition.
Did lots of research on internet about differences, hardware, mods, connectivity, repairs, retro scene etc.
I am not an Electrical Engineer, but I recapped it, changed switching regulator, RGB to scart mod and removed audio from Composite Sync signal.
Connection to my monitor: rgb cable to GBS 8220. And from GBS to monitor VGA.
Now I have two problems:

1 )I am missing brighter shades of colors. If i do BREAK+Reset test -all I can see is only one type of the colors. No subcolors.
I thought maybe I damaged something when soldering, but someone said that GBS cannot reproduce Brightness signal. Is that true? I have seen some owner videos Spectrums running through GBS and no one mentioned missing colors.
I havent got Scart TV to try, but I have ordered cheap Scart to HDMI converter.

2) After about an hour running my +2 I get some kind of small vertical screen jitter. At first it's fine and later it starts to jitter more and more.
It's small amplitude, but it's unconfortable to look at the screen. It's constant and about 4-5 times per second. If I disconnect spectrum for half an hour - jitter dissapears, but than slowly appears again.
I think that's something to do with temperature - computer getting warmer, but I have no idea. Maybe ULA? Someone suggested to get ZX HD and said my problems will dissapear. But I would like to fix it if possible. I dont think its GBS upscaler problem.

So can anyone give me any pointers please.
Thanks, Paul
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Re: New and need help

Post by Dizzy » Fri Jun 14, 2019 10:42 am

Received cheap HDMI to Scart (or Scart to HDMI?) adapter. Connected, but got very dark grey screen, no colors- barely could see anything.
So have ordered ZX HD.
But in the mean time arrived Stereo mod (anyone know if you are supposed to remove old audio jack? or have them both? - instructions were unclear) and after soldering it and doing HAL mod - now my keyboard Enter key does not work! Cursor keys work, but not Enter.
I have double checked for shorts, cold joints, but could not make it work. ULA?
Old electronics are fragile.
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Re: New and need help

Post by 1024MAK » Sun Jun 16, 2019 1:03 am

The normal colours are the less bright shades.
The more intense colours are the bright colours.

In BASIC to get a bright colour, use BRIGHT 1.

The way that the machine generates the BRIGHT colours, it mixes the red / green / blue video signals with the BRIGHT signal. The way in which this is done for the RGB outputs depends on the machine. Some circuitry is in the machine, and some is in the SCART lead. Combined, this circuitry converts the ‘digital TTL’ level signal to an analogue signal that consumer video equipment can understand.
So are you using a RGB SCART lead for the correct +2?

The following 128K models exist:-
  • Sinclair 128K U.K. model (toastrack), uses a 9V PSU which connects using a 5.5/2.1mm barrel plug.
  • Spanish 128K model (toastrack), uses a 9V PSU which connects using a 5.5/2.1mm barrel plug.
  • Amstrad +2 (grey), uses a 9V PSU which connects using a 5.5/2.1mm barrel plug.
  • Amstrad +2A (black), uses a PSU that has +5V, +12V and -12V outputs which connects using a DIN plug.
  • Amstrad +2B (black), uses a PSU that has +5V, +12V and -12V outputs which connects using a DIN plug.
  • Amstrad +3
  • Amstrad +3B (sound fixed)
The RGB SCART lead for a +2 (grey) is different to the RGB SCART lead for a +2A, +2B or a +3.

The only easy way to tell if vertical screen jitter is your converter (or more likely, the converter maybe not completely happy with the slightly nonstandard video signal from the Spectrum), is to connect to a TV using either a SCART equipped TV, or via composite or via RF.

Vertical screen jitter is not normally caused by a faulty ULA / gate array chip.

Cheap SCART to HDMI converters often don’t convert RGB video signals, they only convert composite video. Is yours in a small plastic box, or in a metal box?

You will have to give more details on which stereo mod, as there is more than one type...

Is it just the ENTER key that does not work, or are there other keys that don’t work? Hard to test I know.

All the keys on the keyboard are part of a matrix. So if it is just one key, there is a problem with the mechanism for just that key. If there are a number of keys that don’t work, it could be a break in the conducts of the membrane, or a poor contact between the membrane tail and the connector on the PCB. Or damage to the PCB tracks going to the ULA / gate array chip.

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Re: New and need help

Post by Dizzy » Sun Jun 16, 2019 2:11 pm

Thanks Mark for the reply!

I do have a correct Scart cable for Grey +2, but not having a Scart TV I can not use it. I had connected it through GBS box with my own made cable( 8pin Din to 5 cables(R,G,B,Sync,Ground) to GBS). I know that Scart cable has some circuitry in the Scart end so maybe that's why I am missing colors. But I couldn't see any info about GBS/Bright colors on the internet.
I had conncected through RF to my Samsung TV, but quality was really bad.
Anyway ZX HD is comming my way now. Possibly that will eliminate jitter.

But my biggest problem now is a keyboard. I don't know if it's only Enter key is not working or others too. Cursor keys are working. But I have a feeling it's not the keyboard at fault. It was very clean inside and it was working perfectly before. Ribbons looks good too. Only after I soldered stereo mod (it's a Byte Delight mod) and socketed HAL chip keyboard started not to work.

First I checked for shorts between pins on HAL chip and AY chip. I had re-resoldered HAL chip. I looked into wiring diagram and continuity tested connections from Ribbons to chips and all seems good apart on KB2 Ribbon connector on 2 pins to ZX80 chip and IC7 chip I am not getting continuity.
By that time I was overhelmed and I wasn't sure if I am measure correct, etc.
I have measured the diods on KB2 and they seem fine.
After I was reading about pulling resistors and I was overhelmed again!
So I am not sure how the keyboard matrix working. And how can I test signal from Enter key.
In the mean time I have ordered another +2, but I really would like to get to the bottom of this and fix it.

Thanks Paul

P.S. My keyboard is Z70700 issue 1
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Re: New and need help

Post by Dizzy » Tue Jun 18, 2019 12:51 am

Just want to report that I managed to fix the keyboard issue. It was broken track on a motherboard between one keyboard pin and Z80.
Some time with multimeter and new energy and voila!
Feel good
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