Monitor repairs

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HullQLMan
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Monitor repairs

Post by HullQLMan »

Hi

I know everyone including me are mainly using emulators or replacement systems (Q68) etc but I do like to get the BBQ out occasionally, so over the weekend I plugged one in and the monitor display started scrolling down. Every so often it stops but then starts scrolling again!

Now I have 2 Philips Pro 9CM073 monitors (from EEC many moons ago) with this fault. Is this something to do with whichever circuit controls the horizontal hold? I don't know as I have now electronic knowledge. Does anyone know where I can get them fixed? Is it worth it?

Alternately is there an alternative apart from a TV or has any progress been made on the VGA convertor?


Silvester
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Re: Monitor repairs

Post by Silvester »

A rolling display usually means vertical hold. Might be worth tweaking internal preset (marked VH or VHOLD) to centre in stable region (when set is warm). Though the fact it happens to both monitors is a bit coincidental.

(Horizontal hold usually shows skewed horizontal bands)


David
HullQLMan
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Re: Monitor repairs

Post by HullQLMan »

Forgot to add that when the displays are not scrolling the image at the top curves in slightly.


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Pr0f
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Re: Monitor repairs

Post by Pr0f »

I used to take my CRT monitors to a place in Stevenage - but that was a long time ago - not sure if he'd still be there after all this time. I am guessing due to size and weight you are going to want to find someone local to fix them.

Somethings you could try - particularly if the monitors have been sat idle for any length of time:

1) invest in some switch cleaner and spray the all the control potentiometers (width, hold, trapezoid, etc). Rotate the knobs back and forth over their range - re adjusting them to roughly where they were originally - this cleans up the wiper contact and the track which might be part of the problem.

2) Try a different video input source - such as a VCR or camcorder or another computer - the QL's video output is slightly outside a normal TV spec signal and so pushes some monitors a little to display it correctly.

Finally - a lot of these old monitors will be suffering from component aging - most notably the capacitors in the circuits - and as Monitor manufacturers tend to use components that are 'good enough' they were not built with very long life in mind - if you feel confident taking the back off a monitor - a cursory visual inspection will reveal if any of the electrolytic capacitors - the larger ones with the tell tale stripe have deformed at the cap's or ends which may indicate they have failed.

This is the sort of thing to look for:

https://www.google.com/url?sa=i&url=htt ... AdAAAAABAD

Finally - the internet may provide you with a copy of the service manual for these monitors - which may have a troubleshooting guide - always worth a try - sometimes you can also find other users of this monitor who may have had the same failure and have managed to repair the monitor.

Example for a similar monitor from philips:

https://jestineyong.com/tda2658-ic-repl ... r-monitor/

I would say by word or warning - don't poke about inside a CRT monitor unless you know what you are doing - there are voltages inside that will easily kill you!!


Silvester
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Re: Monitor repairs

Post by Silvester »

HullQLMan wrote:Forgot to add that when the displays are not scrolling the image at the top curves in slightly.
That's a classic leaky electrolytic capacitor problem, I've had replace caps on old monitors to solve that.


David
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Re: Monitor repairs

Post by Ruptor »

Silvester wrote:That's a classic leaky electrolytic capacitor problem, I've had replace caps on old monitors to solve that.
Is it an old age problem or just a dielectric polarisation situation? Could it be dust on the High voltage section dragging the supply down? On 3 phase drives there was problems of inrush on units that had been standing. if we powered them up slowly the cap dielectric recovered but slapping power on they went short and bang! I suppose the TV cap dielectric might already be damaged and you can't apply power slowly but you might be lucky when it warms up it might recover.


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Pr0f
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Re: Monitor repairs

Post by Pr0f »

The problem with a lot of these monitor designs is that temperatures within the monitor are elevated, and so this affects capacitors - likelyhood is that they will be rated for 85C rather than the more expensive 105C, which whilst it is probably 'enough', is still a stress factor. Added to that the working voltages - again in some parts of the monitor you will be looking at not just 5 or 12V, but higher values in the tens of volts or even 100+, and in addition to that, ripple current is also a factor to consider. Current in the capacitor will cause heating affects. Switch mode circuits for power supplies often specify high ripple current and extended temperature range - similar considerations should be given to deflection circuits that drive the coils and the video amplifier.

At the end of the day - like for like replacement of the capacitors will result in extending the life of the monitor. The tube itself will eventually start to degrade (heater element, phosphor coating) - I don't have any long term figures for tube life - the electronics usually packs up long before the tube.


Silvester
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Re: Monitor repairs

Post by Silvester »

That's why I never leave equipment too long without occasionally powering up for a few minutes (at least every 3 to 6 months) so the capacitors don't become unformed.


David
RichardCGH
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Re: Monitor repairs

Post by RichardCGH »

You can get a QL to SCART lead quite cheaply.
Do you have a flat-screen TV with a SCART socket you could use ?


HullQLMan
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Re: Monitor repairs

Post by HullQLMan »

RichardCGH wrote:You can get a QL to SCART lead quite cheaply.
Do you have a flat-screen TV with a SCART socket you could use ?
Hi Richard

I have a QL to SCART lead and a 19" flat screen TV with SCART socket which I can use for the moment, It's just nicer on a monitor.

Thank you all for your help.


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