DWJ
Member
Symptom #1: new-to-me Wells-Gardner 6100 vector monitor powers up, HV crackles, vector chatter is quiet, picture is heavily distorted, about 2" square.
Problem is replicated when using a known good deflection board.
All six chassis transistors look like transistors when ohmed out.
(After rebuilding the HV power supply, symptoms recur. While adjusting B+ to 180V, observed smoke from wires connected to deflection transistor sockets.)
Solution #1: Look more closely at all six 2N3716s... wait, what?
Fix #1: Replace three 2N3716s with 2N3792s, so that the correct deflection transistors are actually paired. *facepalm*
When in doubt, check the obvious stuff twice.
Symptom #2: monitor powers up, spot killer off, picture heavily distorted. X deflection is good (fullscreen), Y deflection is poor (a 2" vertical strip).
Observed R602 still reads 390 ohms, but is charred. Q603 is open from emitter to base.
Replaced R602, Q603, which were likely killed due during the first round of debugging with the bogus pair of 2N3716s. Loosened, cleaned, applied heatsink compound to Q603/Q604/Q703/Q704. Monitor now works fine.
As a precaution, also replaced Q100/Q101, and small capacitors C102/C103, because they took similar abuse when the monitor was being tested with the bogus 2N3716s.
(Interestingly enough, the bogus 2N3716s tested OK despite the abuse, and worked just fine when I cleaned/reapplied the heatsink compound and mica insulators for the three correctly-installed 2N3716s.)
Problem is replicated when using a known good deflection board.
All six chassis transistors look like transistors when ohmed out.
(After rebuilding the HV power supply, symptoms recur. While adjusting B+ to 180V, observed smoke from wires connected to deflection transistor sockets.)
Solution #1: Look more closely at all six 2N3716s... wait, what?
Fix #1: Replace three 2N3716s with 2N3792s, so that the correct deflection transistors are actually paired. *facepalm*
When in doubt, check the obvious stuff twice.
Symptom #2: monitor powers up, spot killer off, picture heavily distorted. X deflection is good (fullscreen), Y deflection is poor (a 2" vertical strip).
Observed R602 still reads 390 ohms, but is charred. Q603 is open from emitter to base.
Replaced R602, Q603, which were likely killed due during the first round of debugging with the bogus pair of 2N3716s. Loosened, cleaned, applied heatsink compound to Q603/Q604/Q703/Q704. Monitor now works fine.
As a precaution, also replaced Q100/Q101, and small capacitors C102/C103, because they took similar abuse when the monitor was being tested with the bogus 2N3716s.
(Interestingly enough, the bogus 2N3716s tested OK despite the abuse, and worked just fine when I cleaned/reapplied the heatsink compound and mica insulators for the three correctly-installed 2N3716s.)
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