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Epson 12" CRT Monitor Q602A

D

DeltaDon

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Oct 26, 2016
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875
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Dutchess County, New York, USA
I just received this monitor as non-working. It is a B&W CRT for the Epson QX-16 computer. Besides the Q602A model #, there's a FCC # of BKM678Q602A on the label plate. It was DOA when plugged in and I opened it up and found a blown 2.5a slow blow fuse. I installed a replacement and now the power light comes on on the CRT's front panel. But no joy. No sound of the high voltage/Hort circuit working. I did see a 1/2W carbon resistor that's blacken around it's middle, but it will be a PITA to reach since the PCB is attached to the lower plastics which has high sides. If anyone has a schematic or perhaps a working example I'd like to know the correct value for that resistor. (Orange, x ,gold???) Picture to follow.
 
I swear searching the internet nowadays is like the game of jeopardy. You have to know the answer to search the question. I had an old expired link to Epson QX model documentation.
Using that link led me to where the remains are now. The Q602 monitor begins at section 2.8 in QX16-tech-ch2.pdf in here https://electrickery.nl/comp/qx10/doc/index.html
I used to own a qx10 so still had the old links.

Larry G
 
Retrogear, thanks for that link, it has more info on the QX machines than I've seen elsewhere. Now I've got to see if one of the resistors shown in the few circuit drawing matches up with the burnt one in the monitor. The measured resistance across the burnt resistor is 2 ohms and the resistor number is hidden under the physical device. I think I snip one lead and lift it up to get the number.
 

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The resistor may or may not actually be the problem. What can happen is if a capacitor on the power line the resistor feeds is weak or open, it will have an AC ripple component that creates an AC rms power across the resistor
that increases the wattage and makes it run hotter. I learned this theory from another very smart repair technician a long time ago. That resistor may have been carboned up for awhile. once the monitor is running, you can decide
what to replace it with.

Larry G
 
I just wish I could read the color bands correctly on the burnt resistor. Checking resistance to ground was done. No short. Yes, there's a lot of troubleshooting necessary yet. Something caused the fuse to blow and so I'm suspecting a failure of a component did that and the component may have then gone open after its sudden failure. I'm also worried about the amount of rust around the fly back. I'd like to thank the designer of the plastic case too. The top clamshell was easy to remove, but the PCB and CRT mounted to the lower case with high sides really really makes measuring anything a royal PITA. Oh, well. It is what it is. I guess spreading the guts out with the case removed is next. At least most of the cap's appear to be Nichicon and so a full recap as a first step in not likely to be necessary.
 
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