More Than 170 Components Replaced In BPL FHR 9307 CRT TV To Bring It Back To Life
This CTV was brought to me by a friend of mine, also a regular customer, living far away in another town. It was brought to take out the Tube as I had a requirement of it at that time. But that customer changed her mind and this TV got stuck with me, more or less like a forced gift. During the lockdown period, as the inflow of sets was stopped, I took the opportunity to clear up my backlogs one by one. Surprisingly, it got on when I powered it, but no display was there. So, instead of scrapping this TV, I thought of reviving it. This TV was reported to have been working when my friend went for a change of TV and was lying neglected in his attic, absorbing moisture and dust. So, I got encouraged to go ahead with my plan.
As always, I opened the TV and subjected it to thorough cleaning. Noticed that fungus had formed in many parts. One disc capacitor in the power supply section was found burst. I went ahead and replaced all the electrolytic capacitors without any hesitation, as it was very much required because of the age of the TV. Then retouched all the soldering points and made it fresh. Replaced the push to on buttons on the control section . Checked for any defective components in the power supply section, after replacing the burst capacitor. Disconnected the jumper B+ going to primary of LOT (FBT) and connected a 100W bulb. My testing plug was already wired through a 200W bulb and I had no hesitation in switching on the SMPS.
The readings were perfect as per the circuit diagram:
So, reconnected the jumper, loaded the board to CRT Tube and applied power. Absolutely no display and horizontal oscillation was not taking place. Looked for any shorted components in the primary and secondary of FBT and did not find any. The suspicion therefore was on the FBT. I removed it and also the H-out transistor. Then checked whether the H-out section was working, by connecting an LED between its base and emitter positions of the transistor on the board. It was lighting up indicating that Horizontal oscillation was taking place. Got a replacement and fixed it along with the H-out Transistor that I had removed. Then when I switched on, oscillation was taking place, as I could measure voltages at the secondary. ABL voltages were missing. So, switched off, waited for the tank capacitors to get discharged and combed the ABL circuit. Found resistors open. Replaced it.
After that when I reconnected the board and checked, there was no display still, though ABL voltage was showing around 7V, which was normal. Checked the CRT and found that voltages were reaching its base:
Suspected the CRT Socket, as it had fungus attack and I had cleaned it thoroughly. So, replaced it. Then the blue screen came up and the picture was having colour patches when a video was played. The surround system was having motor boating sound when activated. Anyhow that was because of lack of proper earthing. An extra wire was connected to its earth point form the tuner section, upon which that got solved. I let the TV run for a few hours. Then the display returned to blue screen and video was missing, though audio was ok. I knew that something is wrong with the video section. Combed the area for any defective components and found a couple of transistors reading abnormal.
So, replaced it. My techie friends also came online to help me out. They asked me to check the wave forms on the pins of Video IC as well as the Chroma IC. And also the CRT Board. THE RGB was getting generated and the luminance and horizontal feedback was also ok. So they advised me to comb the ABL area upto the Digital to Analogue converter, which I did. I replaced the resistors, caps and transistors in that area, even though they did not show any defect in measurement. I was also asked to replace the fixed caps on the CRT board, which I did.
In the meanwhile, in order to ease out trouble shooting, I assembled a Video Amplifier downloading the circuit from:
I assembled only the amplifier part without power supply, as it was not needed by me. Also used only one output and changed the R9 to 150 Ohms instead of 56 Ohms to control the current, as advised in the text. I did this, because the video out from the TV was checked and found to be ok on computer. So, this board came very handy.
Gave video signal to input, wiring the power supply to 12V of Video IC No. LA7955. Please see its circuit diagram given below after this paragraph. But no video. Then gave it directly from this board to Pin No.9 after disconnecting its jumper wire. No video. We (me and my techie friends, who were helping me online) noticed that this Video IC has buffer and it mixes the internal input to give it as a composite video signal at pin 9, which goes to another part mixing it with luminance and splitting it to RGB. So, our trial brought only video with full of grains when we gave the video, reconnecting the pin 9 to LA7955. So, combed the Luminance section and found one transistor malfunctioning and a 11V Zener was also suspected. These were replaced. Then efforts were made to correct the RGB by using the adjuster on the PCB, which produced just a vertical line in the centre, when activated. Picture follows after this paragraph. After this adjustment, the video was missing, even when the sub-bright pot was adjusted. Then my techie friends suggested replacement of all the pots on the CRT Board, as these could create such problems. That was done. See the pictures:
The blue screen as well as the raster was much better now. But something was wrong somewhere. So, the suspicion went to the Luminance Amplifier:
The Transistor 2SA1015 as well as the 11V Zener was replaced, upon which also the video was not coming out. So, I connected this board to another tube and checked. It was perfectly OK. I used another Sharp CRT Board on this BPL Tube. The picture was perfect. Then what was wrong! All my friends were also at a dead end. Anyhow, many days passed during these experiments.
One of them suggested replacement of the CRT socket again, as the new ones also seemed to be creating video problems, which I did! Bingo, the video was back and I adjusted the settings for a good picture. Why was this socket creating problem on BPL TV (Hitachi Tube)? Well, I have no clue! It could be due to some loose fittings! (Anyhow I did not discard the changed socket as I wanted to recheck it on another Tube later)
I let the TV run for several hours and it worked fine. Now I need to give it to an Auto driver only at the cost of replacement of the following parts (Service charges waved as a help to such people who are struggling to meet both ends in this pandemic):
This article was prepared for you by Parasuraman Subramanian from India. He is 72 years old and has more than 30 years’ experience in handling antique equipment like Valve Radio, Amps, Reel Tape Recorders and currently studying latest tech-classes conducted by Kerala State Electronics Technicians’ Association. He has done graduation in BBA degree, private diploma in Radio Engineering and retired as MD of a USA company. Presently working as Consultant to Hospital and other institutions.
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