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Vendex Headstart VGA M-888-VC

chjmartin2

chjmartin2

Experienced Member
Joined
Dec 26, 2012
Messages
439
Hi,

I don’t know specific forum for a monitor but this one goes with a 286 so seemed ok. Anyway, the monitor seems to work great but it keeps shutting off on me, and if I wait a minute and turn it back on it seems to go back on. Anyway, got any ideas on how to fix? Could it be as simple as the switch? I have a chicken stick so not worried about cracking it up to work on it. Here is a video of the behavior.

Thanks,

Chris
 
Think changing out the capacitors.. Its a power issue..
I also have a monitor that powers on, and after 1-2 minutes suddently its powers off again..
Powerboard needs a recap.
 
Sadly I recapped the entire powerboard and I have the same issue. I tested the switch and it doesn’t seem to be that as it goes back on and off seemingly randomly. There are some additional caps on the main board. Cycling the power switch doesn’t seem to matter at all and hitting the side does nothing. Really bummed because the picture is fantastic when it is on and I am sure it is one small component. I need to figure out if the whole power board is shutting down - the power LED shuts off too. Feels like power issue. I really wish I were smarter…
 
I found the "service manual" but it is just badly scanned schematics and a parts list. This monitor is actually a Samsung CQ4551. The power supply acts very strangely. The output voltages are fine until it "clicks" off and then they are all weird. Oddly, if I run the power supply without load it doesn't turn off - in fact even if I turn off the power switch the circuit is live. I was told elsewhere that this is a thermal issue but I have reflowed the solder on the entire power supply. This project is killing me because it is in the way of others. I am close to giving up sadly.
 
When the monitor fails, do you still have a constant (that is, not dropping) DC voltage at C910? It's the big DC bulk filtering capacitor.

Edited: Actually, what powers the LED on the front? Another thing that could be happening is the high voltage detects an overcurrent detection or arc in the flyback or yoke deflection circuit and shuts the monitor down.
 
NeXT said:
When the monitor fails, do you still have a constant (that is, not dropping) DC voltage at C910? It's the big DC bulk filtering capacitor.

Edited: Actually, what powers the LED on the front? Another thing that could be happening is the high voltage detects an overcurrent detection or arc in the flyback or yoke deflection circuit and shuts the monitor down.
Click to expand...
Hi,

My guess is that it is likely something more the later versus the former. The power supply does not change anything when there is no load but it does warm up. It just "feels" like there is something downstream. The LED on the front gets power somewhere from the main board and it does go off when the monitor shuts down. Can an arc be a thermal issue? When it gets warm it happens and then it turns off, cools off a bit and then turns back on.

I will check the DC voltage at C910 - I did swap out all of the electrolytics.

Thanks,

Chris
 
NeXT said:
When the monitor fails, do you still have a constant (that is, not dropping) DC voltage at C910? It's the big DC bulk filtering capacitor.
Click to expand...

155 Volts when the monitor is "on" and 165 Volts when it is off. The other thing that is weird is that there are resistors that are NOT the same values as the schematic BUT do match the values indicated on them. Scratching my head on that one.
 
Ff the display drops out and you are left with a constant DC voltage at that capacitor, you indeed have a fault further downstream rather than a bad power switch. The fact though the power LED goes out as well however concerns me you might have bigger issues, hence my concern if you have arching around the flyback.
 
NeXT said:
Ff the display drops out and you are left with a constant DC voltage at that capacitor, you indeed have a fault further downstream rather than a bad power switch. The fact though the power LED goes out as well however concerns me you might have bigger issues, hence my concern if you have arching around the flyback.
Click to expand...
There is no arching around the flyback unless I can’t see it. I sat in complete dark and watched it go on and off. It felt like there was an issue near one of the resistors on the PS board. It is testing fine and I removed it, but if I spray compressed air on it then the monitor goes on. Could be in my head but I am going to try to swap it.
 
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