Random Degaussing Issues and Monitor Menu Button Changes! (Betson)

[Lakersfan]

Ok, I have a new Betson Imp arcade monitor I got around Sept. I've only had it up and running since the beginning of December. Everything has been running fine until today. Out of nowhere, the monitor is randomly degaussing. I also noticed that my monitor menu settings changed to the Portugese language. Also the monitor menu pops up every once in a while too. So I look at the monitor menu button plate and nothing is pushing a button and nothing seems to be out of the norm with it. In fact, I haven't even touched the plate in a while, so I don't think it's anything I've done. This happens during different games and during the Mala menu. It seems to do it less and less the more the monitor is on; almost as if once it warms up it does it less. But it has never completely gone away. I've tried plugging it directly into the wall (thought at first it may have been a power issue). Oh, and other than the problems mentioned above, the monitor looks perfect.

Any ideas???

[MonMotha]

Check the connector first to make sure it isn't loose.

You can check the following with the remote board hooked up and the monitor on:
At pin 21 of IC502 on the chassis board measure
5V with nothing depressed
0.5V with the exit key depressed
1.5V with the sel key depressed
3.5V with the up key depressed
2.5V with the down key depressed

If you have an analog or high-time-resolution digital multimeter, check to see if those are bouncing around.

If any of those fail or that doesn't give you any other indication, check the connector to the remote board again as well as the resistors and diode on the remote board.  You will probably need to remove the components from the remote board to do this.  Also check the cable where it enters the main chassis board from the remote.  Make sure nothing is pinched, etc.  If you find any bad resistors, replace them.  The service manual says to pay attention specifically to R406, R408, R409, and R410, which I believe are all on the remote board.

[Lakersfan]

Welp, I'll give it a shot. I found the manual and see IC502 on page 36. The manual says to focus on Pin12 but you state Pin21. Is that a typo by chance?

Nonetheless, I'll need to go to my in-laws house tomorrow and borrow his meter. I don't have one yet. So from your post, I gather that all I need to do is turn on the monitor, connect the red end of the meter to the pin and the other (black) end to a ground. Then it should show up as 5V with nothing depressed, 1.5V w/ exit key pressed, etc.? What setting should I have my multimeter set to? Also, I'm not sure how to check diodes and resistors. Any tips for that?

Thanks for the help!

[MonMotha]

Pin 21 is the input from the remote board.  Pin 12 is the degauss output.  Given that you're having random issues with the OSD showing up uninvited, it sounds like it's an issue with that IC receiving what it interprets to be commands from the remote board (i.e. voltages other than 5V), rather than the degauss doing weird things.  Remember that the exit button is also the degauss button if no OSD is up, so that makes some sense.

Yes, take your meter and connect black to ground and red to that pin (21).  Be careful not to bridge pins.  The 10 or 20VDC (whichever you have) setting should be correct for this.

To check resistors, use the resistance (ohms) setting on your meter.  Apply one probe to one lead of the resistor and the other to the other side.  Which probe goes where doesn't matter.  Tracing out the remote board (the schematic is incomplete, notice the extra zener diode and R407; yes there's two R407s...), it looks like you should be able to test them on the board (unplug it from the chassis after power down) presuming the switches themselves are good.  If you get weird readings (i.e. something not expected), remove the resistor from the board and test out of circuit.

R406 should read 100 ohms, R408 should be 470, R409 should be 1k (1000), and R410 should be 2.4k (2400).  Use an appropriate scale.  Anything in the ballpark (the resistors are 5% tolernace) is fine.

The diode (D401) is actually a zener and can't be easily tested with some multimeters.  I can't read the full part number to determine specs on it, either, and it doesn't appear in the schematic.  I *think* it's a 1N5231, which would be a 5.1V zener.  It looks like it's being used as a clamp.  This could cause the failure you're seeing.  If you have a diode check setting, use that.  Apply the red probe to the cathode (side with the black band) and the black probe to the anode (other side).  Should read about 5V, but with the low current multimeters use for test this reading can be erroneous, and not all multimeters will test diodes to this voltage.  You can also check it the other way: should read about 0.5-0.7V.  Again, low test currents can cause this to be low.  Given the circuit, you shouldn't have to remove the diode from the board for this test, but if you are having trouble, I'd suggest doing it anyway.  I don't have an authoritative schematic to go by as the one in service manual I have appears incomplete for the remote board.

[Lakersfan]

This is great information. Thanks so much for the help & clarification. I'll check into it and post my results.

Thank you!

[Lakersfan]

Update:
I tried unplugging the remote board to see if that eliminated any problems. Once it was unplugged all problems went away. I plugged it back in, the problems reappeared. So I unplugged it and the kids played it on and off all day long with no problems. The next day in the afternoon, all of a sudden there was no picture (and yes, the remote board was still unplugged). So I plugged the remote board back in only to find my settings were completely changed. It's almost as if there's a short somewhere causing the menu settings to change. I tried to change the menu settings back and they change while I'm trying to make my changes. So to make a long story short, I haven't had a chance to try MonMotha's suggestions yet, as I worked all day today.

That being said, can someone please give me specifics as to where exactly on the board I can find IC502? I see it on the manual but am not sure where it is located on the actual board. Secondly, if something is shot in IC502, what do I do from that point on?

Thanks guys for helping me.

[Lakersfan]

Alright guys, I'll admit I got a little confused as to what I was exactly looking for. So I just decided to take the easy way out and contact Betson support with my issue. They were extremely supportive and we tried a few troubleshooting things. When nothing seemed to fix it, they offered to replace the monitor chassis. I am fortunate enough to have a handy father-in-law who helped me discharge the monitor and remove the board. I am heading down to the Buena Park office Monday to swap it out.

[qrz]

--BINGO! Either that, or I was attempting to say "before" but it was too many letters to type-- u send it out , check the degaussing thermistor ( i assume it has one ) for cold solder joints.
resolder if needed.

ptc thermistors have a higher resistance when hot . the solder has a tendency to degrade under high heat conditions.   this is a very common occurance in crt tv's

qrz