Schaabpablo
Newbie
- Credits
- 1CR
Hi everyone,
I’m dealing with a stubborn horizontal sync/phase thermal drift on a CRT monitor monitor chassis (Imperial KT1420A / 20" CRT revision). I have attached a video showing the exact symptom.
The Symptom:
When turning on the monitor completely from cold, the image starts severely shifted horizontally (misaligned/out of phase). Over the course of about 45 to 60 seconds (it used to be 1m 40s before some component replacements), the image gradually and smoothly drifts back toward the center on its own. Once it reaches the center, it stabilizes perfectly and stays sharp and locked for hours.
Full Recap & Pots: Performed a full electrolytic recap on the chassis. Brand new high-quality capacitor installed. All adjustment potentiometers, including H-HOLD and H-POSITION, have been replaced with brand new ones.
Small Caps: Removed and tested all small polyester and ceramic capacitors around the horizontal oscillator section (HA11235 jungle chip area); all tested within spec out of circuit.
Resistor Overhaul: Found and replaced three severely out-of-spec/heat-damaged resistors:
R611 (7.5kohms 3W): Was reading low at 6.5kohms and running extremely hot, transferring ambient heat to the new B+ filter capacitor. Replaced.
R608 (2.2ohms 2W): Located in the horizontal snubber/tuning network (connected to a 2kV capacitor C615 and a choke coil). This resistor originally suffered when the old 2kV capacitor failed open years ago. It was reading degraded at 15.68ohms out of circuit and exhibited positive thermal drift when tested with external heat. Replaced with a new 2.2ohms 2W resistor.
R601 (6.8ohms bleeder): Replaced as well.
Current status:
Replacing these out-of-spec resistors significantly reduced the drift time and made the centering movement much smoother, but the cold horizontal shift issue is still present.
I suspect a semiconductor junction failure (thermal leakage) in the horizontal drive/positioning stage (Q401, Q403 which are 2SC1514 transistors, or the HA11235 jungle chip itself). I am currently about to perform a freeze-spray test using a component cooler aerosol to isolate which active component triggers the shift back when cooled down.
Has anyone encountered this specific behavior on this family of chassis? Any specific diodes or feedback loops connected to the AFC window that I should look into?
Video of the failure:
Thanks in advance for any insights!
I’m dealing with a stubborn horizontal sync/phase thermal drift on a CRT monitor monitor chassis (Imperial KT1420A / 20" CRT revision). I have attached a video showing the exact symptom.
The Symptom:
When turning on the monitor completely from cold, the image starts severely shifted horizontally (misaligned/out of phase). Over the course of about 45 to 60 seconds (it used to be 1m 40s before some component replacements), the image gradually and smoothly drifts back toward the center on its own. Once it reaches the center, it stabilizes perfectly and stays sharp and locked for hours.
Full Recap & Pots: Performed a full electrolytic recap on the chassis. Brand new high-quality capacitor installed. All adjustment potentiometers, including H-HOLD and H-POSITION, have been replaced with brand new ones.
Small Caps: Removed and tested all small polyester and ceramic capacitors around the horizontal oscillator section (HA11235 jungle chip area); all tested within spec out of circuit.
Resistor Overhaul: Found and replaced three severely out-of-spec/heat-damaged resistors:
R611 (7.5kohms 3W): Was reading low at 6.5kohms and running extremely hot, transferring ambient heat to the new B+ filter capacitor. Replaced.
R608 (2.2ohms 2W): Located in the horizontal snubber/tuning network (connected to a 2kV capacitor C615 and a choke coil). This resistor originally suffered when the old 2kV capacitor failed open years ago. It was reading degraded at 15.68ohms out of circuit and exhibited positive thermal drift when tested with external heat. Replaced with a new 2.2ohms 2W resistor.
R601 (6.8ohms bleeder): Replaced as well.
Current status:
Replacing these out-of-spec resistors significantly reduced the drift time and made the centering movement much smoother, but the cold horizontal shift issue is still present.
I suspect a semiconductor junction failure (thermal leakage) in the horizontal drive/positioning stage (Q401, Q403 which are 2SC1514 transistors, or the HA11235 jungle chip itself). I am currently about to perform a freeze-spray test using a component cooler aerosol to isolate which active component triggers the shift back when cooled down.
Has anyone encountered this specific behavior on this family of chassis? Any specific diodes or feedback loops connected to the AFC window that I should look into?
Video of the failure:
Thanks in advance for any insights!
