Arcade CRT monitor not powering up every time

[Simon_m74]

Hi,
We have a twin racing arcade game at the Retro Computer Museum in Leicester (UK), and one of the CRT monitors does not want to boot up every time.
About 2/3 the time, it will not turn on - but if it does, its fine until we turn the machine off.
I know its the monitor, as I can hear the game, an I have checked by plugging in an external LCD VGA on to the machine.

Any ideas?

Sorry I cant give any CRT model info at the moment, other than its 29", 4:3, VGA

Simon

 

[kellys_eye]

Probably aged capacitors in the power supply - the symptoms are typical.

Post pictures of the insides of the monitor and look for signs of 'bulging' on the tops/ends of capacitors and/or any leakage of liquids.

 

[Simon_m74]

I`ll try to pop there later tonight to do so - if not later in the week.

I guess caps also - for the `other problem`, we cant centre the screen. its adjusted on the pot to the max/min, but the image is still partially off the left side of the screen.

I`m fine with changing caps - as I have done many times on LCD systems - just never a CRT, as I respect the high voltages, and tbh, a little `over-concerned` about working on CRT systems, other than simple repairs like a dry joint on a scart, or broken function buttons.

But I guess I`ll be `ok` as I DO respect the high voltages - And these monitors self-discharge on power down.

Just a question on my concern...
I know the danger is at the anode connection on the top of the CRT (unless discharged) - and I`m ok to discharge caps... but just to be sure, is the PCB side of the LOP HV too ?
If so - how do I make it safe?

Thanks

Simon

 

[kellys_eye]

You can discharge the aquadag coating using an insulated screwdriver and resistor connected to ground - the same could apply to any hv areas but you're probably looking at the low voltage side of the monitor initially.

Use standard safety practise (one hand behind your back when working/probing ht circuits etc, use an isolation transformer if you have one and definitely use an RCD protected mains supply.)

 

[KJ6EAD]

Most arcade game CRTs (monitors) were made by Wells Gardner or Electrohome. There are "monitor get well" kits available from arcade supply companies and on Amazon and ebay.

 

[Simon_m74]

I had a friend look at this for me.
It turned out that the high-power transistor that feed the lopt had shorted.

After changing that out, for a new one, the monitor powered up (static heard on boot up) - but we heard a `ticking` from the monitor`s PCB.
We`re now suspecting capacitors, that do the timing for the lopt.

So next is to change all the caps.