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Zeroeth level pc monitor repair

The only excuse I have is i don't normally look at the innards of pc monitors. I now have a recent monitor where the biasing of driver for pulse transformer leading to base of the LOPT driver , correctly biased, seem fine but no line rate oscillator, HT etc. With pc monitors is there no free running oscillator that is then pulled into sync by external H & V syncs from the pc ? Is it the case of no external syncs then no monitor oscillator at any frequency?

Perhaps I'm too cautious but the 3 R,G,B signal lines from the pc go direct to the subboard fixed to the CRT neck socket close by to spark gaps and HV components - alien territory to me to see TTL level suff there. I therefore powered up a win95 era pc , known working (with its monitor ) ,

15 pin high density plug format, to feed syncs + RGB to this one but it does not kick into life. Chase the H sync signal lines back to what should be their source on the pc to monitor lead and there is none. Does a recent pc monitor with DDC control lines need a more recent pc ? Is it safe to power up pc with old monitor , unplug that monitor and plug in new monitor or is it some control line I have to enable/disable ?

-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on

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Reply to
N Cook
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VGA signals are not TTL level, they are analogue 75 Ohm video signals. It's very common now for the VGA signals to go straight to the CRT base PCB, and perfectly safe provided basic rules are followed. As you are in the EU, there's very strict laws on electrical safety approvals.

No.

Kind of a hot-swap of monitors? Yes, I do it all the time (for many years) and have never blown a monitor or video card.

No.

Dave

Reply to
Dave D

On Wed, 21 Dec 2005 16:19:00 -0000, "N Cook" put finger to keyboard and composed:

This is how "energy saving" CRT monitors respond to missing sync signals:

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==================================================================== If either Vertical Sync or Horizontal Sync coming from the display controller are removed, the monitor will enter the Standby/Suspend mode. In this mode, the deflection and high voltage are turned off, reducing power consumption in the monitor to less than 30 Watts.

If both sync signals are removed, the CRT filament will be turned off, in addition to the deflection and high voltage. This is the Off mode. The monitor power consumption is reduced to less than 5 Watts. ====================================================================

CGA and EGA were TTL, VGA is analogue. IME, it is very common to find the monitors's video circuitry, eg an LM1203, on the CRT PCB.

I've seen the amplitudes of H & V sync signals on some older graphics cards, eg S3, collapse under the load of some monitors.

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- Franc Zabkar

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Reply to
Franc Zabkar

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