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avatar_Gryzor

Problem with my CTM664 - low brightness

Started by Gryzor, 19:04, 20 August 11

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Gryzor

Hello guys, take a look at this:

Problem with my CTM664...
What you're seeing is the highest brightness setting of my monitor, and the flashes are what happens when I turn the potentiometer. Obviously (?) there's something wrong with it, but what can I do?
Cheers
T
PS At the lowest setting it's quite black...

Jase

The flashing looks like a job for switch/contact cleaner... Look for a tin of Servisol Super-10. Worked wonders on just about every dirty knob (ahem) and switch I have tried it on!

Gryzor

What on earth is a Servisol Super-10? Sounds like a vitamin brand from a sci-fi novel...

...just looked it up. Would WD40 work the same? Although I have opened up CPC monitors in the past I have never taken a close look at the "dirty nob" (tsk, tsk).

I just realised, I don't know if I had this problem before installing Bryce's S-video converter - could this be a problem about the reduced brightness? Although the flashing definitely points to a fault.

MaV

Quote from: Gryzor on 19:36, 20 August 11
I just realised, I don't know if I had this problem before installing Bryce's S-video converter - could this be a problem about the reduced brightness? Although the flashing definitely points to a fault.

The S-Video modulator is partly to blame. Markus has built his into a CPC+ and the picture on a monitor was darker afterwards.

Perhaps it's best to insert a switch?
Black Mesa Transit Announcement System:
"Work safe, work smart. Your future depends on it."

Jase

Quote from: Gryzor on 19:36, 20 August 11
What on earth is a Servisol Super-10? Sounds like a vitamin brand from a sci-fi novel...


An example: http://www.ebay.co.uk/itm/Servisol-Super-10-Switch-Contact-Cleaner-/260433010389?pt=LH_DefaultDomain_3&hash=item3ca3045ed5#ht_500wt_922


It basically cleans and lubricates pots/switches and other similar things. If the volume switch on your hi-fi crackles when adjusting, this stuff will sort it out.


WD40 is not the same thing. I suppose you could try get any other generic brand of electrical switch / contact cleaner. I just know of my old friend trusty servisol. 1 tin has lasted me years, and fixed many, many crackly pots.

CanonMan

Quote from: Gryzor on 19:36, 20 August 11
...just looked it up. Would WD40 work the same? Although I have opened up CPC monitors in the past I have never taken a close look at the "dirty nob" (tsk, tsk).

WD40 is absolutely vile and shouldn't be used on any kind of electronic equipment at all, IMO.  :laugh:

Badstarr

@Gryzor


My GT65 Had the same problem, I spend a lot of time repairing cars and I had some brake and parts cleaner spray, available at any motor shop, carb cleaner is basically the same stuff. I sprayed some into the brightness AND contrast, with the power off obviously! I rotated the dials several times and left it 5 mins to evaporate. I switched on the monitor and it all works perfectly again! Just like new.


I've used the spray before on loads of gummed up electrical connections on my car and it always works a treat, plus its not too bad at cleaning car parts too!


You get loads of it in a can for 4-5 quid.


WD40 is a bad idea as it will strip any insulation on the pots it may work at first but it will do more harm than good  ultimately.







Proud owner of 464 GTM64 6128 GTM65, GX4128 and a 464/6128 Plus Hybrid a 20 year long ambition realised! :-)

Gryzor

Thanks for the advice on WD40 - never used it on electric thingies so I don't know how it would work. I'll try to locate something like Super10 tomorrow, I guess it should be pretty easy to find.

Badstarr, did you spray on the dial without opening the monitor up?

Mav, thansk for the tip. I'll try a switch, should it go on the 5V line or is something more radical required?

Badstarr

I sprayed it on the dial from the front sort of on and in the gaps around it too, just enough to give it a decent coating and moved the dial through a few complete rotations before leaving it to dry/evaporate. I would say whichever solution you use really work the dials a good few times it may also be worth giving the V Hold a going over too just to be on the safe side. You may feel a bit of roughness or friction at first which gradually fades, that should be when the stuff has done it's job (when it operates smoothly).


I've got my GT65 hooked up to my 46128plus and its working fantastic!



Dont go nuts with the spray as it will take longer to dry, I don't think the stuff is particularly flammable but its always a good idea , as I'm sure you know to take care with liquids and electrics. 


Hope it works, remember to let us know how you get on!
Proud owner of 464 GTM64 6128 GTM65, GX4128 and a 464/6128 Plus Hybrid a 20 year long ambition realised! :-)

MaV

Quote from: Gryzor on 23:31, 20 August 11
Mav, thansk for the tip. I'll try a switch, should it go on the 5V line or is something more radical required?

That should be sufficient. We better wait for advice from bryce, because in this configuration the hardware is still connected to the video lines, and that may not be a good idea.

I'll switch on the batman signal light. Bryce? This is commissioner MaV, we need you. ;)
Black Mesa Transit Announcement System:
"Work safe, work smart. Your future depends on it."

MacDeath

QuoteWhat you're seeing is the highest brightness setting of my monitor, and the flashes are what happens when I turn the potentiometer. Obviously (?) there's something wrong with it, but what can I do?
My CPC old colour monitor does the same...

Actually my brother told me he repaired this one in the past by cannibalising another one...

This can be the brightness potentiometer the faulty part.

First try this, or else, this can be more serious and may need to "simply" find a new monitor solution...

Bryce

The RGB inputs of the S-Video circuit are terminated with 75ohm resistors to GND, so if it's connected to the monitor at the same time (which also has 75ohm termination resistors) the screen brightness will definitely be reduced by about a third. Disconnecting the 5V to the S-Video Circuit will NOT solve the problem. You would need to disconnect GND too to bring the brightness back up.

The flickering is definitely just dirt on the knob.

Bryce.

Gryzor

Well, the CPC is not connected to the tv at the moment, only the monitor. So if I understand this correctly it shouldn't affect brightness?

Also, it's definitely NOT one third we're talking about here. I seem to remember that at the highest setting you couldn't really look at it, am I wrong?

Thanks for the feedback!

steve

I think Bryce is saying that even though it is not connected to the television, the presence of the s-video interface will affect the brightness of the monitor by about one third, you would need to remove the 5v and gnd connections (via a switch?), to restore your monitors brightness level.

Gryzor

Well, he did say "at the same time"... but yeah, I see the ambiguity. Are there any double switches one can use or should I insert two separate switches?

Bryce

Ok, second attempt  :D : If the RGB and the GND of the CPC is connected to the S-Video circuit (it doesn't matter whether 5V or a TV or anything else is connected), the brightness will be affected. The RGB input pins are directly connected to GND with a 75ohm resistor (as they should be) which reduces the normal CPC RGB output levels even when the S-Video is not powered or connected to a TV at all.
Technically, the correct way to decouple these would be to disconnect the three RGB signals from the S-Video Circuit, but this would require a 3 way switch, so the less eligant, but equally effective and easier solution is to disconnect the GND to the circuit (which only needs a simple one pole switch). Admittedly, electronic perfectionists will now correctly claim, that you now have three floating points, but in this case that doesn't really matter and won't effect either the CPC or the standard output picture quality.

Bryce.

Gryzor

Ok, so one switch in the Ground line it is. Buying one tomorrow. Thanks for clearing this up!

Gryzor

Well, I did buy a switch today (unfortunately, even the smallest switches are quite big compared to that tiny board!) but before connecting it it occurred to me I had not soldered onto the board but rather used a molex connector (duh...), so I just took it out and by gosh, the screen is so much brighter now... this is much more than a third of difference, when you plug it in! But I guess it doesn't matter - I bet the output it gives to the TV is bright enough, so all's well.

Bryce

Cool.

The bit about 1/3 might have been a bit misleading. It's a logarithmic value, so 1/3 voltage drop would decrease the brightness by more than half.

Bryce.

Gryzor

...more like it :)

The flashes when I turn the knob are still there, though, so there's something wrong with that, too; I did buy some cleaning spray, sprayed it from the outside, didn't seem to do anything except for corroding the plastic a bit. Will have to open the thing...

Bryce

You'll never get to the carbon surface from the outside, you'll have to open the monitor and dis-assemble the knob to clean it properly.

Bryce.

Jase

#21
Quote from: Bryce on 15:46, 22 August 11
You'll never get to the carbon surface from the outside, you'll have to open the monitor and dis-assemble the knob to clean it properly.

Bryce.


From memory, the pot used on the colour monitor has small holes around which the cleaner can be directed into using the straw supplied. but the monitor case does have to be removed to get there.


Take care, there are some huge voltages stored in there... and it is VERY painful when you discharge one of them caps through your arm.


Quote from: Gryzor on 15:03, 22 August 11I did buy some cleaning spray, sprayed it from the outside, didn't seem to do anything except for corroding the plastic a bit



Just concerned as to why the cleaner has corroded the plastic? Is it corroded or clean  :D ?

Pentagon

In some cases its necessary to open the CTM644 and discharge the tube. Then you need to replace all caps and change them to better quality. Also need to change the potentiometer and everything should be fine again. I did that some years ago and mine was like new again. But the caps are weak after such a lot of time and the inbuilt PSU is weak too. You can make it much better and heavier if you change the caps to high quality ones.

Kindly regards
Tom


Nicolas Lecoq

Hello,
Thanks you very much. The potentiometer from one of my old CTM644 has been cleaned by 3-en-Un nettoyant contact (sold in France). 
The picture is now stable. The blue become more brighter after few minutes.
Nicolas

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