Poor quality display on MTX500

About original Memotech hardware.
Post Reply
Matt
Posts: 4
Joined: 21 May 2021 20:17

Poor quality display on MTX500

Post by Matt »

Hi, I'm Matt and I'm new to the forum. I have just got a lovely MTX500 and I need some advice please. Unfortunately it has a very unstable display both on RF and video output.
- When I turn on the screen is very fuzzy and washed out
- After a few seconds it darkens slightly and becomes a bit sharper
- If I enter a line of BASIC it gets darker and sharper still. (Looks like how I imagine it should)
-Occasionally it reverts to a pale fuzzy screen again, but this is erratic.
-If I restart it returns to washed out and fuzzy
Any ideas what the issue is? Thanks in advance
User avatar
Dave
Posts: 906
Joined: 11 Aug 2012 18:16
Contact:

Re: Poor quality display on MTX500

Post by Dave »

Hi Matt

do you have any tools/test equipment? Ideally, you'll have a multi-meter and a soldering iron?

If you don't have a MTX manual, you can download the circuit diagram section here http://primrosebank.net/computers/mtx/d ... hPages.pdf

The first and easiest check (assuming that you have a meter) is to check the DC voltages - a convenient place to measure them is on the VRAM chips (the 8 marked 4116). Check the +5 and +12 voltages in particular as they are used on the video board.

Assuming that the voltages are OK, you probably want to repin the video board to generate mono output only - that bypasses most of the video components and is a good starting point for video issues

regards
Dave
Martin A
Posts: 534
Joined: 09 Nov 2013 21:03

Re: Poor quality display on MTX500

Post by Martin A »

Analugue isn't really my thing, but ...
With the display appatrenlyl getting better with more white on screen I'd be suspecting the output levels from the video board. Modern Tv's can be rather "picky" about levels. If they're not close to spec thn the TV can have issues. The extra white when it's on-screen could be helping cue the TV in.

I've seen something similar withe the output from a ZX80, (which outputs a signal nothinmg like the specifications!)
Matt
Posts: 4
Joined: 21 May 2021 20:17

Re: Poor quality display on MTX500

Post by Matt »

Thanks Dave. I have recently got myself a soldering iron and multimeter so will open up the MTX when I get some time and check those voltages. Will report back with my findings.
Matt
Posts: 4
Joined: 21 May 2021 20:17

Re: Poor quality display on MTX500

Post by Matt »

Thanks Martin - Will try and find an old CRT TV and see if that makes a difference too.
User avatar
1024MAK
Posts: 685
Joined: 24 Dec 2012 03:01
Location: Looking forward to summer, in Somerset, UK

Re: Poor quality display on MTX500

Post by 1024MAK »

If you have a different LCD TV, try that. There is a very wide variation in how well different TVs (even if the same ‘brand’) handle the video signal from a classic home computer.

Also see if there are any menu/settings/controls for switching off and image enhancement or noise reduction.

Mark
Post Reply