Sourcing Transistors

[northpoint]

I have a question about getting replacement transistors. I run into this a lot and would just like some clarification.

So, If I have a bad transistor - lets say the packaging on it says LAPT C4886. I have the hardest time trying to find it from component suppliers like mouser. I eventually find it under another part number 2SC4886. Now I have to wonder - Is this a pin-for-pin direct replacement just under a different part number? Why cannot I find a data sheet for the LAPT C4886 on the chip to make sure? Can I trust the 2SC4886 to be a direct replacement? How would one know if you dont have the originals datasheet?

From what I have recently learned (and correct me if I am wrong) the C in 2SC part denotes a NPN transistor. I have read that the C (or if its a D) denotes a NPN style transistor and if its a A/B its a PNP style transistor.

Incidently, I am working on a very old car amp Kenwood KAC 927

As a side question, Where in the world can one find schematics for products? Would make troubleshooting a lot easier if I could get my hands on a source for schematics. If you dont have access to a schematic I would think your very limited in your troubleshooting (like car amps). There are the power supply mosfets / rectifiers and such that you can test but if its a lot deeper issue like on the inputs do you just call it dead and scrap it ?

I am sorry if my questions sound really basic or stupid. But I guess the only stupid question is one not answered - And if I do not ask then it will just haunt me til I do. Others might benefit from this too down the road

Northpoint

[budm]

Re: Sourcing Transistors

Most Japanese Transistor will have just the Letter and Numbers printed on the body, I.E. 2SCxxx, it will be Cxxx.
A, B, = PNP
C, D = NPN

I have series of these Japanese Transistor that I kept for years:
http://www.ceitron.com/tech/specbook.html

You can search the net for info on the Transistors to verify the pinout of the original Transistor first.

https://cdn.badcaps-static.com/pdfs/...61b3ade8a1.pdf

Lots of places have free service manuals:
www.elektrotanya.com
http://www.hifiengine.com

just do the search for them, some you may have to pay for.
And when the service manual is not available, then I some time will trace out the board, but if you familiar with the circuit topology of what you are working on then it will be easier.
Did you search for the service manual for Kenwood KAC-927? I have no problem finding it.
You have no idea how lucky you are to have internet compared to what I had to do to get the service info in the 70's, 80's, 90's if you think it is hard today.

[Andrew F. Ali]

Re: Sourcing Transistors

Yes, my friend...the 2SC4886 WILL work and IS the direct replacement...They are NPN and not all Class A/B amplifiers use PNP transistors.....Your transistor is an Audio output and the complimentary to work with it in a push-pull arrangement would be a PNP transistor 2SA1860.....Both transistors btw would be shorted...so replace both...I would suggest....

[R_J]

Re: Sourcing Transistors

Would this help? I think its the right one. If the outputs are shorted, check the emitter resistors (R161,R162,R163,R164), and the base drive resistors (R157,R158,R159,R160) and then check the driver transistors Q117, Q125 etc.

[northpoint]

Re: Sourcing Transistors

I want to thank you both for helping me understand. I do have some background in electronics but I have not been doing board level work in years. So, I have to basically learn a lot of things over again. Especially finding sources for stuff. It does get a bit confusing at times and I am glad your both here to help clear up these odd points.

Thank you so much for all the advice. It is very much appreciated!

[northpoint]

Re: Sourcing Transistors

Would this help? I think its the right one.

Thank you very much. The kenwood suffers from a no power condition and I tested the C4886 by taking it out of circuit and I get basically about .375 whether I test with the lead base positive or negative. Since this is a NPN type I get the following results:

Using multimeter in diode mode:

Base Collector emitter
pos 326 327
neg 320 320

emitter to collector: 000 (either way with leads) shorted?

My testing shows its bad.

Thank you.

[rhomanski]

Re: Sourcing Transistors

When you get replacements, check the pinout. Several I have bought have been changed by the manufacturer. The 945 and 733 come to mind. The originals were EBC and the replacement were ECB. If the holes are triangular it's not hard but if they are in a straight line you have to insulate a leg and cross the B and C.

[northpoint]

Re: Sourcing Transistors

Just wanted to top off this post with an update. This is the first amp that I have ever repaired. I am almost done with it. Its actually has a 5A relay that is bad. After turning it on I have to tap it with my screw driver to get it to click over and drive the outputs. lol.

The relay is no longer available wouldnt you know - VB 24SMBU-522 . I do believe this is a good replacement for it:

http://www.mouser.com/ProductDetail/...252bK9FQ%3d%3d

I actually powered it up today after replacing the ouput transistors and a mosfet in the power section. Tapped it with my screw driver handle and it plays pretty good.

Just want to say thank you.

Next on my bench is the dreaded Powerbass ASA 800.2x amp. I am still looking for the schematic for it. This suffers from no output. Im at the point where I need to see a schematic of it to go any further.

Thanks very much for all the kind help.

[budm]

Re: Sourcing Transistors

Are you getting 24Vdc on the relay coil?

[northpoint]

Re: Sourcing Transistors

Are you getting 24Vdc on the relay coil?

Getting 23Vdc on each coil (there are two relays in this model). Incidently, I took the relays out to look them up and when I put them back in it starts to work now. Cold solder joint?

Everytime I spend hours on a problem and finally decide to post I seem to answer problems myself or find them easier. I always seem to come off foolish.

Thanks for your reply.

[R_J]

Re: Sourcing Transistors

You might want to check for poor solder connections on the relay (s) there are 2, are both causing problems or just one channel?

[northpoint]

Re: Sourcing Transistors

You might want to check for poor solder connections on the relay (s) there are 2, are both causing problems or just one channel?

It was both channels. But after a resolder they started working. See my earlier post.

Learning all the time - thank you.