RCA Flybacks for PTK169 mislabeled from the factory
I had problems with flybacks for an RCA rear projection TV while working on commission at a TV shop in Shelton, WA. Searches at the time turned up no useful information regarding this, so after I figured out what was going on, I thought I'd post it on NesdaNet and maybe help another technician avoid many wasted hours. Originally posted March 2003.
We ordered a 232191 IHVT from Union Electronics. This was for a PTK169.
The first one we received failed to work. Many hours troubleshooting time spent and unneeded replacement parts were installed determining something was wrong with the new flyback. (Holly at Union again verified the part number was correct.) Another was ordered again from Union. Again many hours of time was spent determing that this part was also bad. This was confirmed when a known good flyback from a working set was substituted temporarily and the set fired up and worked beautifully.
A third transformer was ordered, this time from Andrews. (Willy at Andrews also verified we were ordering the correct part). The part from Andrews arrived and worked just fine. All 5 transformers, the original, the one from the working set that was used as a substitute, and all three new flybacks had the same part number on the flyback, 2G25018 and TCE 30.0KV. All three new flybacks had the part number 232191 on the boxes.
During the course of checking the transformers against one another we discovered that apparently the 2 from Union were MISLABELED AT THE FACTORY! They appear identical on the outside with one exception: The two original FB's and the 3rd successful FB all had a green ink splotch about 1/2 to 3/4 inch in diameter on them, whereas the two that did not work had no such splotch. I don't know how significant that is.
We determined that these transformers were made to be used in the direct view chassis and were MISLABELED AT THE FACTORY.
According to the tests we performed here, it has to do with the way pin 6 is connected on the direct view VS the PTV-- In the Direct View CTC169, pin 6 is the low end of the Anode winding. In the Projection PTK169, the black wire (also present on the Direct View flyback) is the low end of the Anode winding and is connected to a circuit that looks like it monitors beam current and limits peak brightness.
Symptoms of the wrong FB in the Proj set:
Standby is just fine. Hit PWR: Momentary Horiz drive. 200V line only
goes up to about 100 or 120V and the 26V line goes up to about 36V, as
measured on a 'scope. If you short pin 4 of T4101 (Run regulator
feedback) to hot ground as per the official Troubleshooting manual,
R4762 (430 ohms 1W) on the HV Reg PCB (mounted on the H.O.T. heatsink)
blows the magic smoke. This HV Reg PCB is not present in the Direct
View set.
How to test before installing the FB to make sure that you
have the
correct one:
Using the Sencore VA48, Horiz SCR output, connect ground to pin 1 and
drive to pin 11. Use your scope to adjust to 10V positive peak pulse
drive. Here's the key to the test: If you measure the anode voltage
using the wrong pin as ground/common, the voltage is too low. The exact
voltage is very sensitive to the drive voltage, so comparison is the
key.
I'm sure you see the pattern. :'/ A cross check of the Thomson PTK169 service manual on CD vs our paper Thomson CTC169 is inconclusive as the schematic of the PTK169 FB circuit labels the low end of the anode winding as pin 6. The PTK169 service manual lists the replacement part as 232191.
I have wasted somewhere around 100 hours of my time, plus the time of the other techs and the owner at HQ, plus the time of other techs on NesdaNet. And many unneeded parts were installed. The customer has waited months for this set and is not happy, and in the end it turns out it could have been back to him in the first week of January.
I'm not a happy camper. I hope this post saves some other techs hours of wasted time.
Steve Greenfield
Shortly after I posted the above and forwarded it to RCA, without any comment from RCA, all of the flybacks for PTK 169 became unavailable for a month or two. Then just as mysteriously became available again.