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TonyDuell · 24th Jul 2022, 10:05 am

I suspect it is the same board then. It'll take me some time to get round to scanning the diagram though

The monitor section is quite conventional. The CRT voltages come from the flyback transformer (line output transformer). The monitor is powered from the 12V output of the power supply, the CRT heater is run straight off that. Since the heater is glowing, the 12V rail is present, my guess is an issue in the horizontal side.

Start with the CRT pin voltages, what do you measure on pins 5 (control grid), 6 (first anode) and 7 (focus anode). Be careful, the last 2 should be a few hundred volts (all are less than 1kV). If they're all missing, sounds like a line output stage fault.

Line drive comes from pin 7 of IC41. This directly drives the driver transformer L430. Secodary of that goes to base and emitter of Q44, the line output transistor. Although the collector of same is tied to the 12V rail, this is not an emitter follower, due to the drive being connected base-emitter it's a common emitter amplifier as normal. T401 is obviously the line output transformer.

So, check line drive, check Q44, doing a ringing test of T401 I guess.

24th Jul 2022, 10:05 am	#8
TonyDuell Dekatron Join Date: Jun 2015 Location: Biggin Hill, London, UK. Posts: 5,222	Re: HP 150 Touchscreen II repair I suspect it is the same board then. It'll take me some time to get round to scanning the diagram though The monitor section is quite conventional. The CRT voltages come from the flyback transformer (line output transformer). The monitor is powered from the 12V output of the power supply, the CRT heater is run straight off that. Since the heater is glowing, the 12V rail is present, my guess is an issue in the horizontal side. Start with the CRT pin voltages, what do you measure on pins 5 (control grid), 6 (first anode) and 7 (focus anode). Be careful, the last 2 should be a few hundred volts (all are less than 1kV). If they're all missing, sounds like a line output stage fault. Line drive comes from pin 7 of IC41. This directly drives the driver transformer L430. Secodary of that goes to base and emitter of Q44, the line output transistor. Although the collector of same is tied to the 12V rail, this is not an emitter follower, due to the drive being connected base-emitter it's a common emitter amplifier as normal. T401 is obviously the line output transformer. So, check line drive, check Q44, doing a ringing test of T401 I guess.