Wanted: CM14 monitor

[CraigsBar]

Hi Folks,

My CM14 has dies after several years of hard service. Although I have got a MM12 and a scart lead to a 20" LCD TV, there is nothing quite like the original display.

If anyone has a spare CM14 they would be willing to sell me (and post to Ireland - I'll obviously pay the postage) then let me know what sort of price you are looking for.

Many thanks

Craig

[dragon]

I've see today,an announce.edit:He send outside spain.But i not know the exact type monitor he shell.

http://www.todocoleccion.net/antiguo-monitor-amstrad~x25864939

[Bryce]

Define died. Everything is repairable except glass.

Bryce.

[Badstarr]

I have seen a couple of CPCs recently on ebay that had the CM14 monitor it would be worth doing a search. But as Bryce says it could be worth repairing if you are competent with a soldering iron. You could shell out for a new monitor but the exact same thing could happen again. Items of this age tend to die in similar ways and most CPC kit has now exceeded its life expectancy a few times over now. Unless the tube has gone bang a repair maybe more cost effective.


Good luck either way! 

[MaV]

But as Bryce says it could be worth repairing if you are competent with a soldering iron.

The problem is not the soldering for most of us amateurs. You can master soldering with low voltage parts.

It's the high voltages in a crt monitor that makes us uneasy. You can't learn to master that by just reading some text book, but by being shown a couple of times and learning with an instructor.

Even then ... I for example am left-handed, so I'd probably touch those parts much more likely with my left hand, and anything that earthes itself through that hand will go straight through my heart. And speaking of heart - my family on my father's side have weak hearts. To sum it up: I'm not going to risk it, unless I'm being shown how to do that very often and then know what I'm doing 100%.

So, just looking for a monitor is an option to some of us.

[Bryce]

Very wise advice. While I would recommend novices to have a go at fixing a CPC that has a maximum of 12V inside, a CRT is a completely different animal and you should definitely only open it if you know what you are doing. On the other hand, there are still many small TV repair shops that are experts in fixing exactly this type of hardware. It might be worth bringing it in to have it fixed there. Unless the UHT transformer or tube is damaged, it shouldn't cost much to get it back working.

Bryce.

[Badstarr]

I absolutely agree with all that you have said MaV! I was waiting to see if Craigsbar would post a description of the fault before I would have recommended he go ahead and would have warned about the dangers too. There are lots of nasty surprises to be found in a CRT monitor even an LCD for that matter. Large capacitors have been known to hold their charges for an unbelievable amount of time, and the CRT can give you a good dose of X-Rays and the electronic discharge from the tube could potentially stop your heart.


On the other hand though, I believe that most sensible intelligent people are capable of repairing most electronic faults as long as they take their time and take time to avoid dangerous parts. This all depends on having good instructions and advice. I have taught myself how to repair faulty electronics but being a bit dizzy at times I have at various point nearly blown myself to bits! So I retrospect I really should have warned Craigsbar of the dangers in my last post! I'm giving myself a slap on the wrist right now! 

[CraigsBar]

Thanks all..

OK Here's the story...

The Tube  was VERY badly scratched on the front.  (Unfortunate house moving/storage incident, and the rest of it has been canibalised to get my MM12 back up and running (Curly Cables etc)

I do now have a working MM12, and the 20" LCD TV has worked fine until the release of  Edge Grinder which plays so jerkily it is unplayable. On the MM12 and 21" CRT it is super smooth (with the exact same scart cable) to I guess the Plus is working fine, it just does not like Edge Grinder (or Super Caldron) on an LCD TV.

So Ideally I'd like a CM14 (Putting a 21" CRT on a CPC takes up WAY too much room LOL)

Regards

Craig

[Badstarr]

Well Craigsbar this may interest you. I have just purchased a rather nice Technika 16" HD TV for the bargain price of £67.97 from TESCO (I'm assuming you are in the UK?) This may turn out to be cheaper than a CM14 and has a rather nice picture, it's not retro I suppose but it seems fine with my 464plus which has had some mod made to the RGB that causes some unexpected behaviour ie rolling on CRT or Flicking off and on.


It is a wide screen so you my have to live with a slightly squished display if you opt for it



The picture seems very stable with this TV it maybe flickers once after turning on and after that the picture seems fine! Even the interlaced picture on Orion Prime is rock solid stable! I have not investigated exactly what is going on with the previous owners mod to my CPC but off the top of my head there is a diode soldered from the +5V line to one of the pins on the RGB out, maybe to boost the gain or sync or something weird like that. I don't want to remove it before I know why it's there! So the one off flicker could be down to the unknown mod.


Anyway just thought I would let you know about this option!

[Bryce]

Seeing as Craigsbar wanted the monitor shipped to the republic of Ireland, I assume he's there and not in the UK

@Badstarr: All correct and good advice, except for the bit about X-rays?? The only way x-rays could escape is if the glass broke, and when that happens the tube would only work for a few milliseconds before it died completely (without a vacuum, they burn out just like a bulb). Definitely not enough to harm you. The strength of the x-rays produced by a CRT is miniscule anyway.
Can you tell us exactly where or what pin the diode is connected to, then I can tell you what it's doing (if anything).

I know I've mentioned this several times before, but I'll mention it again, for those who missed it: Generally LCD screens are fine for connecting the CPC through SCART, but any games/demos that mess around with the refresh-rates / scanline frequencies will not work properly on LCD, only CRTs will get this right and unfortunately there's no magic circuit that can fix this problem.

Bryce.

[dragon]

Edge grinder for example not work good in a lcd.

And in the future oled tvs can it work?

[Bryce]

No, it will be the same. The problem is not the technology used for the disply, but the method used to get the analogue SCART signal to the display. CRTs send the analogue input signal directly to the CRTs scan circuitry, so any sudden changes to the frequency are automatically passed on and displayed correctly on the screen. TFT/Plasma/OLED TVs use a processor to sample the incoming signal at a constant rate and then produce a still picture that gets displayed.  Changing frequencies suddenly causes it to produce a flickering or completely messed up picture. This will happen with all non CRT displays.

Bryce.

[Badstarr]

Lol, looks like I missed the Ireland bit when I logged in last night! I probably should have read the original post. It could be possible to buy online maybe?


As for the X-Rays, well that was something my science teacher told me when I was at school and I was telling him about an old colour TV I had managed to repair (rolling picture caused by a dry joint on a pot on the PCB). He told me that if it was turned on and the tube was malfunctioning I could have been exposed to (as he put it) a lot of x-rays. He even took up half the lesson explaining that to my class! That has stuck with me until I just read you post Bryce! Now I think about it it does seem a bit odd that a plastic case is enough to protect against the x-rays he was talking about! Just goes to show what can happen if well meaning but misguided teachers give you erroneous information! That said though, I have seen stickers on the side of tubes warning about xrays! So that was kinda confirming he was right for all these years.


As for the TV, it definitely seems to be ok with weird screen modes, I will keep trying other stuff and see what happens. It's not perfect as I say it seems the frequency goes out of range maybe once when the machine is turned on but it seems fine after that.


EDIT: Maybe my science teacher had read something like this... Television and Computer Screens | Radiation Protection | US EPA

[Bryce]

Well to explain it as short as possible: The x-rays are a by-product which are produced when the pixel mask (a metal sheet directly behind the Glass of the screen) gets bombarded with electrons. The sides of the tube are usually lead coated to reduce the amount escaping, but obviously the front (where the picture is shown) isn't lead coated and most of it excapes here. Holding your face directly in front of the screen is probably the worst you can do (as we did for years before PCs got LCD). The base of the tube (where the PCB is connected) is also unprotected so some could escape here. But it's not like there's a bottle of x-rays in there that could leak out if broken, they are only produced while the TV is running and even then, they are so weak, that you'd have to spend years in front of the TV before they would have any negative effect. So you needn't slip into your lead-coated Jock-strap when repairing the TV High voltages are your real enemy.

If you do decide to repair a TV then it should always be unplugged first. Then before you touch anything on the PCB you need to discharge all the large capacitors. I do this with a standard 220V bulb, that I've added two old multimeter leads to. Touch the leads across the capacitor terminals, if the cap is well charged, the bulb might glow for a fraction of a second. Don't short the caps with the head of a screw-driver or piece of metal. It will discharge ok, but may damage the cap in the process.

Bryce.

[Badstarr]

I suppose the fear of xrays caused me to be very careful when it came to monitor/tv repair as I would usually only ever work on it with it unplugged, make some repair then plug it back in to check it worked unplug and try again if not. I never thought of using a light bulb to discharge the caps, I always used to use a huge damaged celestion speaker which would result in a large pop sound when it discharged (I can hear Bryce telling me off already!). Since the advent of TFT screens I rarely have had cause to open a screen for repair maybe just once to replace a CFL.


So the fear of x-rays probably caused me to use better methods for the wrong reasons! Mind you there is no accounting for "voids in thinking" which I'm quite prone to, on one occasion I grabbed a CRT monitor PCB while it was plugged in. The PCB made a rather interesting burn pattern on my hand, I guess I got off lightly! 

[Bryce]

The Speaker solution is an interesting method, it would discharge the capacitor ok, but I'm sure the speaker wouldn't last very long and when the coil finally burns out it's no longer discharging the caps. It's the "thinking voids" that hurt the most and could end up killing you. I've had more than my fair share of them too 

Bryce.

[Gryzor]

@Badstarr: this reminded me of the scene in BBC's Electric Dreams where it showed people using radiation meters to test their microwave ovens back in the '80s...

that you'd have to spend years in front of the TV before they would have any negative effect

Isn't that what we did with the CPCs?

[Bryce]

Exactly!

Bryce.

[Badstarr]

Maybe Dr. Bruce Banner really loved his CPC with GT65 monitor?