Hello Everyone;

New here and to electronics, hoping to get answers to some basic questions.
I'm trying to fix my Sanyo TV, model DP4280. A got a repair kit for the main board for the symptoms its having. However when I had a close look at the board I noticed transistor Q1670 has a small burn on the case. I tested it and got 0.699V and 0.701V respectively. Which would indicate its still good.

I'm not an electronics technician, by any stretch of the imagination, I know enough to get myself into trouble, that's about it. I know transistors can't always be tested in the circuit. Not sure about this one. Was my in circuit test OK or did I get a false good reading because of the circuit its in, as per the attached schematic?

Second question, the Sanyo service manual gives the transistor part numbers and descriptions for the Q1670 as: I assume it could be any one of the three listed?

Part Number Description

T2SC3928A1R-P TR 2SC3928A1R
T2SC3928A1S-P TR 2SC3928A1S
TXXLBB006—-P TR MMBTSC3928R

I found a transistor that matches with part number: 2SC3928A

I don't know is if its the correct replacement, since I have not be able to determine what 1R-P at the end of the part number means, anyone have any idea? Are they simply manufacturers numbers or do they signify some additional specs for the original transistor? In other words, can those numbers be ignored and use any 2SC3928A transistor, if its available, or any equivalent part?

Any help would be appreciated.

Thanks,
Tico

 

Testing components in circuit is generally not a reliable indication of part health. The small burn mark indicates that the part was stressed by having one or more of its maximum limits exceeded. The part may still be "functional" but will be more likely to fail sooner than an unstressed part.

 

Does it work in your TV ok? If it does stop worrying.

It's a 50V 200mA @hfe 200 Npn

 

I know enough to get myself into trouble, that's about it. I know transistors can't always be tested in the circuit.

It would be more accurate to say they can rarely be tested in circuit. When you apply power to the junctions, you're powering other components in the circuit.

You can test junctions for dead or alive condition (open/short), but you can't do much else.

The manufacturer of the Jud Williams curve tracer claimed they had made a discovery of how to use in-circuit waveforms from transistors to do "signature" analysis. They claimed that the distorted waveforms could be used to determine if the circuit was functioning correctly.


These are the curves for a transistor measured in-circuit. It makes the transistor look like it has horrible leakage.

 

learned a bit more today. Thanks for the info

 

I don't know is if its the correct replacement, since I have not be able to determine what 1R-P at the end of the part number means, anyone have any idea?

Could have something to do with how they were packaged (TR = Tape Reel) and binning. A datasheet might give more information.

 

Does it work in your TV ok? If it does stop worrying.

It's a 50V 200mA @hfe 200 Npn

The TV is not working so no way to know at this point. Replacing it and the other components that came with the kit may get it working again. Thanks for the info on the npn.

 

Could have something to do with how they were packaged (TR = Tape Reel) and binning. A datasheet might give more information.

Thanks. I'll try looking at the sheet for the one I found see if it has any additional info.

 

Thanks for the info on the npn.

Japanese 2SC transistors usually have a different pinout than North American (2N) and European (BC) transistors in TO-92 package. It seems that there was agreement on the pin order for SOT-23.

Note: the transistor on the right isn't the same polarity. It was the only one I had handy.

 

Ok so it's not working, so what is the problem with it then?

Is this the circuit diagram?
https://www.manualslib.com/manual/1024363/Sanyo-Dp42840.html#manual

 

Mine is the same model, but Chassis No. ends in 01 instead of 00. There are some differences, but I don't know what they are. The main board is the N7AL version. Problem is no picture/sound. It starts (green light on), screen flashes then turns off after 30 seconds. Continues doing this until you shut it down, then just repeats the same cycle.

 

Japanese 2SC transistors usually have a different pinout than North American (2N) and European (BC) transistors in TO-92 package. It seems that there was agreement on the pin order for SOT-23.
View attachment 223091 View attachment 223092
Note: the transistor on the right isn't the same polarity. It was the only one I had handy.

Thnaks for the info. Luckily the manual shows the pinouts for the transistor. I'll just have to make sure whatever one I can get has the same pinouts as the image in the manual.