Display problem
Display problem
I've been testing one of my 3 Zeddy's and the display is strange.
It's got a working 2C158E ULA which I've tested in another working Zeddy and it boots to a K and works fine.
However in it's own Zeddy, which has tested CPU, RAM and ROM and a ZXvid composite mod, the display is 'italic' lines moving to the right.
No amount of adjustment works with either pot in the mod.
I haven't tried another ULA, as I'm a bit hesitant to do so.
I wonder if anyone knows what this is?
It's got a working 2C158E ULA which I've tested in another working Zeddy and it boots to a K and works fine.
However in it's own Zeddy, which has tested CPU, RAM and ROM and a ZXvid composite mod, the display is 'italic' lines moving to the right.
No amount of adjustment works with either pot in the mod.
I haven't tried another ULA, as I'm a bit hesitant to do so.
I wonder if anyone knows what this is?
- 1024MAK
- Posts: 5122
- Joined: Mon Sep 26, 2011 10:56 am
- Location: Looking forward to summer in Somerset, UK...
Re: Display problem
First, the 7805 NEEDS a heatsink.
Secondly, I don’t have a ZXvid and don’t know any details of this board.
As long the +5V supply is within specification and as long as none of the ULA output pins are shorted, it’s worthwhile trying another ULA.
I presume this is a UK spec. board?
Mark
Secondly, I don’t have a ZXvid and don’t know any details of this board.
As long the +5V supply is within specification and as long as none of the ULA output pins are shorted, it’s worthwhile trying another ULA.
I presume this is a UK spec. board?
Mark
ZX81 Variations
ZX81 Chip Pin-outs
ZX81 Video Transistor Buffer Amp
Standby alert
There are four lights!
Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb
Looking forward to summer later in the year.
ZX81 Chip Pin-outs
ZX81 Video Transistor Buffer Amp
Standby alert
There are four lights!
Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb
Looking forward to summer later in the year.
Re: Display problem
Looks like the hand drawn PCB UK issue one at first glance.
@ sP1d3r
I know you say the RAM has ben tested but have you tried it with a memory pack attached (should you have one) as this would at least eliminate that as the external memory switches out the internal chip.
The "pots" only control brightness and contrast respectively I think.
The ZXvid, I believe, was designed by our very own Andy Rea, so perhaps he may have some input should he read this.
@ sP1d3r
I know you say the RAM has ben tested but have you tried it with a memory pack attached (should you have one) as this would at least eliminate that as the external memory switches out the internal chip.
The "pots" only control brightness and contrast respectively I think.
The ZXvid, I believe, was designed by our very own Andy Rea, so perhaps he may have some input should he read this.
-
- Posts: 2174
- Joined: Sat Nov 26, 2016 2:42 am
Re: Display problem
Mutant Caterpillar Games sell these so may also be able to help.
ZX80
ZX81 iss 1 (bugged ROM, kludge fix, normal, rebuilt)
TS 1000 iss 3, ZXPand AY and +, ZX8-CCB, ZX-KDLX & ChromaSCART
Tatung 81 + Wespi
TS 1500 & 2000
Spectrum 16k (iss 1 s/n 862)
Spectrum 48ks plus a DIVMMC future and SPECTRA
ZX81 iss 1 (bugged ROM, kludge fix, normal, rebuilt)
TS 1000 iss 3, ZXPand AY and +, ZX8-CCB, ZX-KDLX & ChromaSCART
Tatung 81 + Wespi
TS 1500 & 2000
Spectrum 16k (iss 1 s/n 862)
Spectrum 48ks plus a DIVMMC future and SPECTRA
Re: Display problem
Thanks, Mark,
Yes, I'm only testing this board at the moment and I'll replace the 7805.
The board should boot up and work without one, I'd have thought.
Yes, it's a UK spec board, I might try another ULA but I'll look over all the other components first.
Much appreciated, Moggy, I've tried my issue 3 16K ram pack but there's only a pattern of blocks thus far, I hope that the ram pack ULA isn't fried.Moggy wrote: ↑Fri Nov 03, 2023 3:54 pm
@ sP1d3r
I know you say the RAM has ben tested but have you tried it with a memory pack attached (should you have one) as this would at least eliminate that as the external memory switches out the internal chip.
The "pots" only control brightness and contrast respectively I think.
The ZXvid, I believe, was designed by our very own Andy Rea, so perhaps he may have some input should he read this.
My third Zeddy which was a part-assembled kit has a ZX-CCB and both the 2C184E ULA that came with the kit and the 2C158E work in it.
Cheers, Lardo, hopefully I'll find something wrong with the board that causes this, I thought I'd been over all the components but I might not have.Lardo Boffin wrote: ↑Fri Nov 03, 2023 5:34 pm Mutant Caterpillar Games sell these so may also be able to help.
Re: Display problem
Since my previous post I removed the ZXvid, connected the ULA output direct to the modulator output pin the same as my Zeddy with the vLA81 and tried the same in this board but the output was similar diagonal lines.1024MAK wrote: ↑Fri Nov 03, 2023 3:01 pm First, the 7805 NEEDS a heatsink.
Secondly, I don’t have a ZXvid and don’t know any details of this board.
As long the +5V supply is within specification and as long as none of the ULA output pins are shorted, it’s worthwhile trying another ULA.
I presume this is a UK spec. board?
Mark
I removed and tested both ZTX 313 transistors, also the CPU, RAM and ROM, I can only assume a board fault I haven't discovered or a duff crystal.
All components look OK, the 7805 output is 4.96V from my meter
- 1024MAK
- Posts: 5122
- Joined: Mon Sep 26, 2011 10:56 am
- Location: Looking forward to summer in Somerset, UK...
Re: Display problem
It’s a resonator, not a crystal. Also occasionally referred to as a stick of gum!
They do sometimes fail. As do crystals.
Do you have a ‘scope?
Or if you don’t, there are some tests that can be done with a logic probe or similar. Or failing that, a digital multimeter.
Mark
ZX81 Variations
ZX81 Chip Pin-outs
ZX81 Video Transistor Buffer Amp
Standby alert
There are four lights!
Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb
Looking forward to summer later in the year.
ZX81 Chip Pin-outs
ZX81 Video Transistor Buffer Amp
Standby alert
There are four lights!
Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb
Looking forward to summer later in the year.
Re: Display problem
Thanks, Mark, I have a scope and I can check for a 3.5 MHz signal on pin 14.
I wonder if these 6.5 MHz ceramic resonators are common, or whether a little PCB and a newer SMD crystal/resonator could be substituted?
The vLA81 has it's own SMD clock but it doesn't have to interface with ZX81 logic directly, as far as I can tell.
- 1024MAK
- Posts: 5122
- Joined: Mon Sep 26, 2011 10:56 am
- Location: Looking forward to summer in Somerset, UK...
Re: Display problem
The vLA81 does indeed have it’s own clock. It completely ignores the main board resonator. In a ZX81, the master clock is the ULA clock. All timings are derived from the ULA master clock.
And yes, suitable resonators are still available from some suppliers.
Mark
And yes, suitable resonators are still available from some suppliers.
Mark
ZX81 Variations
ZX81 Chip Pin-outs
ZX81 Video Transistor Buffer Amp
Standby alert
There are four lights!
Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb
Looking forward to summer later in the year.
ZX81 Chip Pin-outs
ZX81 Video Transistor Buffer Amp
Standby alert
There are four lights!
Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb
Looking forward to summer later in the year.