Wells Gardner D7700 partial vertical collapse fix

[Ken Layton]

Just fixed a 19" Wells Gardner D7700 digital monitor which had an odd vertical collapse symptom. The top half of the picture was collapsed and folded onto part of the bottom half. Really strange, so I jumped right into replacing the vertical output IC 301 Type TDA 8172 (crosses to an NTE 1788). Powered up and still had the same symptom so the IC was not the problem. So I decided I should check the electrolytic capacitors on the main board. They all checked 100% fine with my ESR meter, so the caps were good.

Finally, pulled up a schematic for that model from the Wells Gardner website (they have very little information on this model) and found diode D301 is tied to the vertical output IC. I checked the diode in-circuit with my analog ohm meter and it checked really funny. So I unsoldered it and checked it out of the circuit. It tested OPEN. It's a type 1N4937 fast recovery 600 volt @ 1 amp (crosses to NTE 552). I replaced the diode and bingo..... beautiful picture again!

D301 is located directly behind IC301's heat sink so I'm sure heat probably played a factor in it's death. You can also substitute NTE 558, SK3843, FR104, or FR107 for D301.

The exact model number on the monitor I repaired is WGE1977-HOGS39A and built in 2008.

Be advised if you recap the main board and you use the capkit listing by "Modessitt", there are two mistakes in the capacitor locations. He has "C427" and it should be C247 (1 uf @ 50 volt). Also, he left out C513 (220 uf @ 25 volts).