By Steven J. Greenfield
I had problems with flybacks for an RCA rear projection TV while working on commission at a TV shop in Shelton, Wash. We ordered a 232191 IHVT from a supplier on the West Coast. This was for a PTK169, which is an RCA rear projection television.
The first one I received failed to work. Many hours troubleshooting time spent and unneeded replacement parts were installed determining something was wrong with the new flyback. The supplier again verified the part number was correct. Another was ordered, again from the same supplier. Again, many hours spent determining 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 flyback transformer was ordered, this time from a supplier on the opposite coast, in an attempt to get a flyback from another batch. That supplier also verified we were ordering the correct part. The part arrived and worked just fine. All five 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 two from the original supplier were MISLABELED AT THE FACTORY! They appear identical on the outside with one exception: The two original flybacks (the one from the TV being repaired and the known-good used flyback) and the third successful flyback 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. A quality control mark, maybe?
We determined that these nonworking transformers were made to be used in the direct view chassis and were MISLABELED AT THE FACTORY.
According to the tests we performed, it has to do with the way pin 6 is connected on the direct view versus the PTV. In the Direct View CTC169, pin 6 is the low end of the Anode winding. In the Proj 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 flyback in the projection 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.
* Proj flyback using black wire as common on 10M DMM: 220 to 230Vdc.
* Proj flyback using pin 6 as common on 10M DMM: 150 to 160Vdc
* Direct View flyback using black wire as common on 10M DMM: 150 to 160Vdc
* Direct View flyback using pin 6 as common on 10M DMM: 220 to 230Vdc
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 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. I’m not a happy camper.
When doing my research on NESDANet, I found that this had been a problem for several years. Techs were ordering parts from alternate suppliers, modifying TVs, using used parts with customer approval, or sometimes just telling the customer that the needed parts weren’t available.
I posted about this on NESDANet and forwarded it to RCA. Shortly after that, without any comment from RCA, all of the flybacks for the PTK169 TV chassis were recalled from the suppliers and became unavailable for a month or two. Then just as mysteriously they became available again, this time with the correct labeling.