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Servicing Rising Model NO.TV-509 5.5” CRT TV Monochrome
I was given a 5.5” CRT B/W TV by one of my friends, an expert service technician himself, almost 10 years back in a condition that audio would not work, very poor image, intermittent problems etc. and he told me to keep it or throw it if it cannot be repaired. As usual, my interest was aroused because of my liking for reviving sets that are discarded by others!
That time, I did a thorough cleaning of the PCB and inside, replaced all the electrolytic capacitors on the board, lubricated switches and connectors etc. and the TV worked well and has been serving me as monitor for servicing all video playing devices. For the audio, as the IC was missing on the board, I connected a TBA810 board and connected an external speaker since the speaker was also bad! I was not using the Radio side of this TV, as the connectors were found removed and never made any attempt to revive it or check that portion.
Recently, this TV developed a problem; a thick horizontal line started appearing on the top with a few more lines, and after sometime the picture will shrink to the middle with only one line in the middle, which is a vertical failure. If switched off and switched on again after a few minutes, this will repeat.
So, I opened the TV and after going through the preliminaries, I dismantled it completely.
As you can see, this is a very cute TV and very easy to handle. After discharging the anode, disconnected the anode wire and looked through the IC datasheet that I had downloaded long back.
(The above image was taken while I was half way through in replacing suspected components)
There is a single IC, D2915CP, which handles all the functions and is the center of this TV. If any of you are interested in looking at this antique piece, here is the link: (I am sorry, I could not locate the original link from where I had downloaded the English version of the datasheet)
I tracked the Vertical section of the IC, pin nos 26, 25, 24 and the connected circuits. The first suspicion on such failures will be on the pots. So, replaced the Vertical Hold and Height Adjusting pots. But there was no improvement. There was no dry solder on the board. Then I removed one leg of all the components in the vertical section and removed the three transistors C1815, C8050 and C8550 from that section. Checked and found all of them were ok. ESRs of the capacitors were also perfect. On suspicion of failing on load, I replaced a few capacitors and resistors in the vertical output section that goes to the vertical coil. The coil was already checked by me with the Ring Tester and Multimeter and found to be ok. Then I removed the IC and did a thorough cleaning for re-fixing it, as sometimes this will solve the problem.
Replaced the IC, but condition was same. (Incidentally, this board is again a good design as values of components and reference numbers are printed on board. But the main IC number is different from what is printed, though! Perhaps a modification done later!) I was baffled! Then I looked for any components getting heated up like transistors in the vertical section. I observed that C8550 was slightly warm and C8050 also was very slightly warm. So, I knew the problem was lying in and around there. Once again removed the three transistors and compared the HFE with that of new ones from stock. The C8550 was showing abnormally low HFE when compared to the new one. It was just around 100, whereas the new one showed around 300. So, I replaced all the three transistors. The TV worked well! But, to my dismay, failed after working for about 2 hours, with burning smell emanating from inside the TV. I disconnected the power, and immediately opened to see that the C8050 and C8550 that I replaced had burnt:
Since I had already checked all the components thoroughly in the vertical section, what would have caused this? The possibility is poor quality of transistors. So, I experimented with SL100 and SK100 (mounting it in opposite direction of Transistor mounting marked on board, as the Base, Collector and Emitter were in reverse order in these two transistors). The TV worked well, but the transistors were getting slightly warmed up. Then I tried with BF421/422, as these are usually used in CRT PCBs for the RGB grids. It worked well, but again to my surprise the transistor was getting warm. Because there was not much space inside the TV, fixing a heat zinc was not possible. So, I replaced the transistors with BD139/BD140. (This was easy, as the board had provision for mounting both type of transistors which have pin 1, 2 and 3 as ECB and EBC. See second image and arrows in the second image above. The numbers given there are A928 and C2338). Since these transistors are rated for 1.5A, I assumed it won’t fail like the 8050/8550. But these transistors were also getting slightly warmed up!
Then, I removed the four diodes and the filter capacitors from the AC input circuit from the board, where a two pin connector was available, for the AC input. As you will notice from the rear cover picture given on the top, it had facility for AC input. But why they have mentioned 220V AC in, was surprising, as the input was directly rectified and fed to the B+ line without any step down transformer or other components! Probably, there might have been an AC adaptor, which was not there when I got the TV. Then I wired the two pins for 12V output and connected a mini 2” Cooling Fan, fixed it on the side of the rear cover, where the defective speaker was fixed. Why the transistors were getting hot remained a mystery. If the coils were responsible, it will fail again. Probably due to ageing! I have no clue and may have to wait and see.
Having done this much, restored the LM386 audio IC circuit, by providing all the missing components, looking through the markings on the board. Mounted a small speaker in the space available between the PCB and front cover, soldering a two pin connector at the end and inserted it at the socket provided at the rear, where the original speaker was connected. Inserted the connector that comes from the side board (Radio/Tuning), as this board has RF input for a built-in tuner in it, and the tuning is manual. This too works well.
Assembled the TV again and let it run for hours and days together. But it did not fail! When I replaced the 8050/8550 with BD139/140, the raster was also better, reason for which beats me!
Now, see the wonderful sharp images it is capable of reproducing, in spite of its age: (These are before cleaning the top acrylic cover)
The following is after cleaning the cover (Playing a DVD player under test)
Here are the components replaced, minus the two burnt transistors, images of which were already given earlier. (I had put back the pots as these were found to be ok) You can also see images of the diodes and filter caps removed from the AC input section, one diode of which broke while removing!
A job well done and added to my ‘satisfaction’ Bag! (Looks like an ‘avaricious’ bag, LOL)
This article was prepared for you by Parasuraman Subramanian from India. He is 68 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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