A928 TRANSISTOR DATASHEET PDF
ST 2SA PNP Silicon Epitaxial Planar Transistor for audio power amplifier The transistor is subdivided into two groups, O and Y, according to its DC current. PNP Epitaxial Silicon Transistor. Absolute . Design. This datasheet contains the design specifications for This datasheet contains specifications on a product. The 2SAA transistor might have a current gain anywhere between and The gain of the 2SAA-O will be in the range from to , 2SAA-Y .
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I was given a 5.
As usual, my interest was aroused because of my liking for reviving sets that are discarded by others! That time, I did a vatasheet cleaning of the PCB and inside, replaced all the electrolytic capacitors on the board, lubricated switches and connectors etc.
For the audio, as the IC was missing on the board, I connected a TBA 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 transistkr that portion. Recently, datxsheet TV developed a problem; a thick horizontal line started appearing on the top with a few more transixtor, 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 dtaasheet. 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. 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 Yransistor pots. But there was no improvement. There was no dry solder on the board.
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Then I removed one leg of all ttransistor components in the vertical section and removed the three transistors C, C and C from that section. Checked and found all of them were ok. ESRs of the transistlr 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 datasheeet components and reference numbers are printed on board. But the main IC darasheet is different from what is printed, though! Perhaps a modification done later! Then I looked for any components getting heated up like transistors in the vertical section. I observed that C was slightly warm and C 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 C was showing abnormally low HFE when compared to the new one. It was just aroundwhereas the new one showed around 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 dagasheet the TV. I disconnected the power, and immediately opened to see dataxheet the C and C 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 tdansistor quality of transistors. So, I experimented with SL and SK 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.
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The TV worked well, but the transistors were getting slightly warmed up. It worked z928, 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. 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 fransistor image and arrows in the second image above.
The numbers given there are A and C Since these transistors are rated for 1. But these transistors were also getting slightly warmed up! Then, I removed the four datashet 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. 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 LM 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. This too works well. Assembled the TV again and let it run for hours and days together.
But it did not fail! Now, see the wonderful sharp images it is capable of reproducing, in spite of its age: These are before cleaning the top acrylic cover. 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!
This article was prepared for you by Ddatasheet Subramanian from India. Presently working as Consultant to Hospital and other institutions. Your feedback on the post is welcome. Please leave it in the comments.
You can also forward this website link to your friends and colleagues-thanks! They used UPC for osc.
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But it’s great to see these old models pulled out of retirement by if I may say it us old geezers and put back into service! Good job Parasuraman, and thanks adtasheet the chip datasheet in the article. To be able to compare them with their specs and with each other.
Because all transistors were getting slightly warm which doesn’t tell much. And I wonder if they worked differently if the set only was used playing on batteries. But without service manual or schematic these things probably always will remain a small mystery. Well, I did not check current drawn by traneistor section, as the transistof is unknown. Base to Emitter was checked as a routine exam.
Did not check on battery. YES, it is commonly used in Adapters! Your email address will not be published.
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