Hi there, first of all i'd like to say im completely new to CRT's, but I intend to learn all I can in the hope of fixing my beloved monitor. I'm a second year physics student, so I should be with the electronics provided I put a bit of reading into it. Any help would be highly appreciated.

Ever since I bought my monitor second hand I noticed every now and then the monitor refused to turn on. The power light would show but after a few seconds the screen failed to 'fire'. I noticed that this happened whenever the monitor was cold. If I left a window open all day, or if it was a cold winters morning the monitor failed to turn on. When warm the monitor worked fine, often running in 1600x1200 at 85hz.

This has recently got a lot worse (about 12 months later), and due to the cold weather in Britain recently I had resorted to first warming up the monitor with a hair dryer (believe it or not!) before turning it on. As bizarre as that sounds, it did actually work... until the other night.

The monitor failed to turn on at all. I heard a pop and noticed a smell I could only recognise as a blown capacitor (might not be though, i've not much electronics experience). Now what happens is the power light comes on, and stays on, but the tube never fires up and the osd doesn't work. Its as if everything is working except the tube. I've not opened up the case yet, I thought i would ask for help here.

I've seen a few posts on this forums mentioning compenents that often fail under similar circumstances. I was hoping someone else here could enlighten me a little more as to what could be wrong with my monitor.

Thanks a lot in advance, and sorry for the long post.

Cheers,

John

Hi your problem is was caused by C932 this is in the HT feedback circuit and goes low in value and more importantly high esr, this lets the psu go too high output especially from cold start.

Now something has died either the HOT Q503 has gone S/C but sometimes one of its parallel diodes D501, D502, D511 if so it will have taken out axial fuse R961, the other item that can die under this condition is the video output IC this takes with it an axial fuse in the 80V line I can not remember if this is on the video PCB or the Main PCB.

Rich

Cheers richard, thats great help. If i get hold of a multimeter, do you think i could pinpoint exactly what failed components i need to replace from the list you've just given me?

Thanks again,

John

Yes I should thinks so.

Rich

Hi, after reading your post and a few older ones i went and bought a multimeter, but sadly the multimeter i have does not measure capacitance so i am unable to test the capacitors you mentioned as of yet. I did check a few components mentioned in a previous post however.

First I checked the H-DY connector for a solder crack but couldn't find one, that was all fine.

Q503 however failed the test i found in a previous post. C-E reistance was around 145ohms rather than several mega ohms as it should be, so is it right to assume that i need a replacement 2SC5570?

You mentioned R961, D501, D502, and D511 might also be a problem. If Q503 is dead will i still need to check the other components? Does C932 need replacing also?

Finally, I have as yet been unsuccessful in removing the mainboard from the chassis. Any tips on this would be greatly appreciated.

Thanks again!

John C

Hi if the transistor was at fault then the diodes should be OK.

R961 is an axial fuse not a resistor as you would think from the circuit reference, C932 should always be replaced on these units.

To remove the board you have to remove all the metal work with the board then remove the board.

Rich B

Thanks a lot Rich. Right, so R961 is probably blown and will need replacing right? I'll get C932 replaced aswell. Do you think C932 is the reason the monitor failed to start when cold all the time?

Thanks a lot for your help Rich, if i get all of this right it will have saved me buying a new monitor!

John C

The capacitor is the main rason for failure of this model and others with a sinilar chassis.

Rich B

thanks to your info about the caps i was able to fix my dieing pro510 for <$1

thank you