Hi all,
Here's one for the CRT people. I have several Hantarex MTC 9000s in my game collection that suffer from the usual problems, i.e. their LOPTs go bad one after the other. I've bought replacement units from Dönberg (Eldor brand) and eBay (generic Chinese brand), and while I'm not a trained TV technician, I have elementary training and experience in desoldering/soldering and understand the basic concepts.
I have installed new LOPTs and cap kits on two monitors now, after they died an abrupt death (screen went black mid-game, no glow/HV at tube, 30W resistor got extremely hot, judging by the repair guides this should be a textbook case). However, once I've done the replacement and reconnect the unit, it immediately blows a fuse - either the supply fuse on the cabinet, or the 128 V circuit fuse on the motherboard. The latter blew very violently (disintegrated). I am using a 120 volt isolation transformer, so this should not be an issue. The cabinet that blew a fuse was working perfectly before the screen died.
The repair guides and schematics that I've found on the Internet seem to deal with a specific chassis PCB model (the "basic" model, with AC supply on the right of the PCB). However, most of my MTC 9000s, and indeed many of those that have failed, are of the type "BY 03" (AC supply on left next to the signal input). It appears to have most of the same components (transistors, ICs, high-power resistors, most capacitors), but in a different order on the PCB. For example, many repair guides tell me to suspect ZD1 if the supply fuse blows, but there is no ZD1 on the BY 03 PCB.
I checked the diodes on the rectifier bridge (out of circuit) and they check out fine, as did every other diode I could find. I have replaced the power transistors (TIPL 762, BU 508) just in case. No components appear visually broken. My solder joints are good as far as I can tell. I have a strong feeling that there is something I am missing here.
Here's one for the CRT people. I have several Hantarex MTC 9000s in my game collection that suffer from the usual problems, i.e. their LOPTs go bad one after the other. I've bought replacement units from Dönberg (Eldor brand) and eBay (generic Chinese brand), and while I'm not a trained TV technician, I have elementary training and experience in desoldering/soldering and understand the basic concepts.
I have installed new LOPTs and cap kits on two monitors now, after they died an abrupt death (screen went black mid-game, no glow/HV at tube, 30W resistor got extremely hot, judging by the repair guides this should be a textbook case). However, once I've done the replacement and reconnect the unit, it immediately blows a fuse - either the supply fuse on the cabinet, or the 128 V circuit fuse on the motherboard. The latter blew very violently (disintegrated). I am using a 120 volt isolation transformer, so this should not be an issue. The cabinet that blew a fuse was working perfectly before the screen died.
The repair guides and schematics that I've found on the Internet seem to deal with a specific chassis PCB model (the "basic" model, with AC supply on the right of the PCB). However, most of my MTC 9000s, and indeed many of those that have failed, are of the type "BY 03" (AC supply on left next to the signal input). It appears to have most of the same components (transistors, ICs, high-power resistors, most capacitors), but in a different order on the PCB. For example, many repair guides tell me to suspect ZD1 if the supply fuse blows, but there is no ZD1 on the BY 03 PCB.
I checked the diodes on the rectifier bridge (out of circuit) and they check out fine, as did every other diode I could find. I have replaced the power transistors (TIPL 762, BU 508) just in case. No components appear visually broken. My solder joints are good as far as I can tell. I have a strong feeling that there is something I am missing here.
