This RPTV was going to be thrown out. "Do you want it?" "Sure," I said. 
Took the back off and tried to power it up. Standby supply brings main supply up, closes relay across 'soft start' resistor (R9A02, 2.2/5w). Drops out after a second or two. Fault code is 2/3, horiz deflection failure. During the attempt, you can -just- hear the vertical yokes. CRT filament voltage is ~6.5 volts at connector 'KF'. This is regulated by Q5A36 from ~8.5 volts derived from winding on horiz yoke TX. The FBT has its own power MOSFET and drive IC. Drive pulses for that IC are obtained from Q5A37.
Horiz defl path:
horiz drive from jungle ->Q5A33(drives base of horiz drive xsistor)
Q5A33 ->Q5A32(horiz drive)
Q5A32 ->T5A32(drives base of HOT)
Q5A31(HOT) ->T5A31(horiz out for yoke only, NOT FBT)
Voltage to T5A31 is regulated by Q5A01, 02, 03
Voltage to T5A32 is regulated by Q5A34, 35
That's horiz defl, now on to high voltage...
An emitter follower, driven by a capacitive voltage divider off of Q5A31, drives a line. This signal is 'HPULSE.' It goes back to the jungle and back to the convergence gen of course. It also drives the input of the SIP module that drives the gate of the MOSFET that drives the FBT. IC5A00 handles everything for the HV, with exception of a quad opamp, IC5A01, for HV regulation/beam current. HV is sampled by a resistive divider in the splitter block and also by a 'proportionally derived secondary' in the FBT, which feeds D5A57. A dual opamp, IC5A02, aggregates these measurements, and if params exceed setpoints/noninverting inputs, trips xray protect.
If I disconnect the 'KF' plug, I get audio, tuners and inputs. No raster of course and the power/timer light will then flash code 1-2 (no err). Odd- with no h or v deflection, no error. But with that board hooked up, it complains...
Occasionally, while cycling power, I hear the tubes charge. I also hear the FBT squealing in pain. This is an HDTV- the horiz freq should be at least double, yet something is audible. It's a beat note! Ripple from the PS and the horiz freq are mixing! The sum or difference is audible in the FBT and a little less so in the power TX. Who'd think Mits would use general purpose caps in this room heater?!
I had the chassis out to check the usual suspects for shorts. Did not check convergence amps thoroughly- only checked from +/-24 to GND, not from either supply to the sub-yokes...
Before I pull the guts out again, I'd like to hear any tips you guys have. Maybe there are things I can check before I pull it out again and start the hunt...
TIA,
-Paul
PS- no corrosion from the coolant, at least in a quick peek.
I can't upload the schematics PDF, I found them here:
http://www.opweb.de/model.php?id=2700
Took the back off and tried to power it up. Standby supply brings main supply up, closes relay across 'soft start' resistor (R9A02, 2.2/5w). Drops out after a second or two. Fault code is 2/3, horiz deflection failure. During the attempt, you can -just- hear the vertical yokes. CRT filament voltage is ~6.5 volts at connector 'KF'. This is regulated by Q5A36 from ~8.5 volts derived from winding on horiz yoke TX. The FBT has its own power MOSFET and drive IC. Drive pulses for that IC are obtained from Q5A37.
Horiz defl path:
horiz drive from jungle ->Q5A33(drives base of horiz drive xsistor)
Q5A33 ->Q5A32(horiz drive)
Q5A32 ->T5A32(drives base of HOT)
Q5A31(HOT) ->T5A31(horiz out for yoke only, NOT FBT)
Voltage to T5A31 is regulated by Q5A01, 02, 03
Voltage to T5A32 is regulated by Q5A34, 35
That's horiz defl, now on to high voltage...
An emitter follower, driven by a capacitive voltage divider off of Q5A31, drives a line. This signal is 'HPULSE.' It goes back to the jungle and back to the convergence gen of course. It also drives the input of the SIP module that drives the gate of the MOSFET that drives the FBT. IC5A00 handles everything for the HV, with exception of a quad opamp, IC5A01, for HV regulation/beam current. HV is sampled by a resistive divider in the splitter block and also by a 'proportionally derived secondary' in the FBT, which feeds D5A57. A dual opamp, IC5A02, aggregates these measurements, and if params exceed setpoints/noninverting inputs, trips xray protect.
If I disconnect the 'KF' plug, I get audio, tuners and inputs. No raster of course and the power/timer light will then flash code 1-2 (no err). Odd- with no h or v deflection, no error. But with that board hooked up, it complains...
Occasionally, while cycling power, I hear the tubes charge. I also hear the FBT squealing in pain. This is an HDTV- the horiz freq should be at least double, yet something is audible. It's a beat note! Ripple from the PS and the horiz freq are mixing! The sum or difference is audible in the FBT and a little less so in the power TX. Who'd think Mits would use general purpose caps in this room heater?!
I had the chassis out to check the usual suspects for shorts. Did not check convergence amps thoroughly- only checked from +/-24 to GND, not from either supply to the sub-yokes...
Before I pull the guts out again, I'd like to hear any tips you guys have. Maybe there are things I can check before I pull it out again and start the hunt...
TIA,
-Paul
PS- no corrosion from the coolant, at least in a quick peek.
I can't upload the schematics PDF, I found them here:
http://www.opweb.de/model.php?id=2700
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