I have a Mitsubishi WT 46807 wide screen HDTV - ready projection now about 6 years old. about 2 years ago I had a problem with the STK's and convergence. initially I was able to clean the chassis and the problem went away for a couple months (too much heat) after consulting a repair tech. and looking at upwards of $500 I decided to repair myself. when I said that I might consider replacement he offered to take the set off my hands but offered no $$ I found the 2 STK's he quoted at $75 for $8 Found the STK's were poorly heat sinked (grease on PCB not STK) Replaced and worked fine until 2 weeks ago.
Current Problem: Initially it appeared as a cold start on the RED gun. Color would come in over 15 minutes. (warm up) Now it looks like I have lost RED all together. When I go into convergence I have only a blue adjust and cannot see any RED hues. I do have some of the manual quoted below: 2 or 3 times we did hear a "chirp" as quoted from the manual below.
CRT Filament Supply The CRT Filament supply is not generated by either Switch Mode Regulator. It is generated in the collector circuit of the Horizontal Output transistor, Q5A31, as shown in Figure 3-5. The horizontal drive signal induced in the secondary winding of T5A31 is rectified by D5A33, and regulated by Q5A36, using IC5A05 as the reference.
HV Circuit 12 Volt Supply It was stated that the 12 Volt supply for the HV Drive circuitry (IC5A00) was derived from the +24 Volt supply. Figure 3-6 shows this circuit in more detail. The 10 Volt reference for the circuit is derived from the Protect circuitry. A comparator in IC5A01 compares a sample of the voltage from the emitter of Q5A08 to the reference. The output of the comparator controls the conduction of Q5A08 to maintain a constant 12 volts.
Note that the 12 Volts supply is routed through the DK (HV Block) connector to pin 9 of IC5A00. This removes HV drive if the DK connector is unplugged, protecting the circuitry from excess HV. If the 24 Volt supply is lost, the immediate symptom is no HV. The 24 Volt supply also supplies power for the Vertical and Convergence Output ICs. A defect in either of these circuits can blow the 24V Supply fuse, F9A04, and the symptom appears as no HV.
Before spending time troubleshooting a no HV problem, we suggest checking the 24 Volt supply to make sure it is not a Vertical or Convergence Problem.
Troubleshooting the Switching Mode Regulators in the V17 is similar to that in previous models. Dead Regulator
1) Check for DC (170V) at Drain pin of the IC. 2) Check for Startup voltage at the VIN input of the IC, it takes 16 Volts to start the oscillator.Dead Regulator (may have a Clicking Sound) OVP may have shut down the oscillator. When this occurs, the oscillator will not start again until the voltage at the OVP input drops below 6 Volts. This usually occurs in just a few seconds. Before condemning the IC, measure the voltage at the OVP input, if it is 6 Volts or higher, try resetting the circuit.
To reset the circuitry:
1) Remove AC power from the set. 2) Use a 100 Ohm resistor to discharge the capacitor at the VIN input. C9A23 for IC9A20, and C9A51 for IC9A50. 3) Reconnect the AC power, the problem may be solved.Regulator Cycles On and Off
1) Additional DC voltage to maintain oscillation may be missing. 2) Check the additional DC source, D9A22 for IC9A20 and D9A54 for IC9A50. ***No Regulator Output and a ***Chirping Sound *** 1) Usually indicates excessive load. 2) Check each of the secondary supplies for excessive current drain (the 110V supply load is the most likely cause).To help isolate the problem, a 60W lamp can be used to replace the 110V load.
We heard a couple times a "chirp" I have some schematics but have not fully explored...
Thoughts? Help? Thanks - Glen