modessitt
Volunteer: Encyclopedia Submission Moderator
First of all, I'd like to thank Ducksan for making the Type 55 power section the same as the Type 20, even though one is CGA and the other is VGA.
Also, I'd like to thank Ken Layton for sending me his repair write-up. Even though it didn't help in this case, it did answer some questions I needed answered (like where to get the schematic).
I know some of you like this kind of stuff, and this chassis isn't seen often (unless you work on older Merit countertops). Here ya go:
Chassis Model: - Ducksan Type 20 CGM-1301
Symptom(s): - Dead. No neck glow or high voltage.
Troubleshooting: - Per Ken's repair guide, I replaced C805 with a 10uF 160v cap, even though it had already been replaced at some point. When that didn't work, I suspected the U801 switching regulator control IC. I was measuring 166vdc on pin 8, but nothing on the other pins. This is where the Type 55 came in. As they both used the same U801 (STK73410), I pulled it from the Type 55 and put it in the Type 20, but got the exact same result. Either both U801's were bad, or there was another problem. I put the U801 from the Type 20 into the Type 55, and the Type 55 powered up just fine. Okay, U801 is not the problem. So, I started going through the resistors in the PS section. In circuit testing revealed two that didn't read properly - R801 and R805. Pulled R805 and it measured properly out of circuit. Pulled R801 and it measured as open.
Solution: - R801 was open. Replaced and monitor now works perfectly.
Also, I'd like to thank Ken Layton for sending me his repair write-up. Even though it didn't help in this case, it did answer some questions I needed answered (like where to get the schematic).
I know some of you like this kind of stuff, and this chassis isn't seen often (unless you work on older Merit countertops). Here ya go:
Chassis Model: - Ducksan Type 20 CGM-1301
Symptom(s): - Dead. No neck glow or high voltage.
Troubleshooting: - Per Ken's repair guide, I replaced C805 with a 10uF 160v cap, even though it had already been replaced at some point. When that didn't work, I suspected the U801 switching regulator control IC. I was measuring 166vdc on pin 8, but nothing on the other pins. This is where the Type 55 came in. As they both used the same U801 (STK73410), I pulled it from the Type 55 and put it in the Type 20, but got the exact same result. Either both U801's were bad, or there was another problem. I put the U801 from the Type 20 into the Type 55, and the Type 55 powered up just fine. Okay, U801 is not the problem. So, I started going through the resistors in the PS section. In circuit testing revealed two that didn't read properly - R801 and R805. Pulled R805 and it measured properly out of circuit. Pulled R801 and it measured as open.
Solution: - R801 was open. Replaced and monitor now works perfectly.