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Transistor markings Questions

oldvinyldude

oldvinyldude

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I have a KA7002 integrated. I have some sporadic noise bursts that are audible with no source playing. My hunch is one or more failed transistors, as the unit uses transistors marked C458 and C871. I gather these are 2SC458's and 2SC871's-correct?

Members here have posted suggested substitutions:

For the 2SC458-use KSC1815 EDIT-I see I should use KSC1845 for this, not 1815!
For the 2SC871-use KSC1845-can anyone confirm these substitutions please?

Another question-on the board, I see 2 variations on the markings for the 2SC871's. Some are labeled C871 55E, while others are marked C871 54E. If the KSC1845 is a suitable sub, can it be substituted for both originals?

Kenwood used both on the same board-there must have been some reason to use both. What might that be?

These will be my first transistor replacements, so I am very much a newbie-I appreciate any guidance!
 
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I own two of these units and find them well-built and reliable unless abused.
First try to isolate the problem area by switching to each input source to see if it originates in one of the pre-amp or tone control sections. Isolating the problem will save a lot of time later. If each input is noisy then the problem may be in the main amp section or power supply.

Second thoroughly clean all the switches with Deoxit. It may take two or more passes. This stuff is not cheap but it is very effective.

Third check your serial number. Two versions exist; the break is at s/n 410501. Units below this s/n have the protection circuit on a separate board, those above have the protection circuit integrated with the main amp board.
Go to HiFi engine and download the service manual: https://www.hifiengine.com/hfe_downloads/index.php?kenwood/kenwood_ka-7002_service.pdf

If you plan to work on the unit yourself obtain a 40-60 watt small soldering iron and a solder sucker or solder wick. I use wick: MG Chemicals #426-NS, 1.5 mm.
Be very careful to only use as little heat as possible to remove components. Make two short passes to remove the solder rather than one long pass. Too much heat will loosen the foil strips.

Search through the AK forum for more information this unit; there is lots of excellent information on this unit and repairs in general.

I hope I have not insulted you with these basic steps.

Best of luck,

Dave
 
No offense taken.

I will do more isolation testing, but as both the above transistors are known offenders, I plan on replacing them all. My questions are about the markings and why there are two variants of the 2SC871's, and to confirm the substitution types.

I have done all the cleaning, deoxit treatments, and I have a Hakko iron, and a solder sucker iron, plus wick, if needed.

btw-my unit has no serial number on the back, but I do see the following stamped on the back plane edge\bottom It's covered when the bottom panel is in place. It reads A23-0198-02. Could that mean my SN is 19802? (very early version)?
 
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Thanks for the batch number clarification ecluser and avionic.

I have bought a supply of KSC1845’s, as a few threads with cross references for subs, suggested they are correct.

Should I get the 1815’s instead?
 
KSC1845 and KSC1815 are good replacements. The 1815 has a higher current limit, the 1845 has a higher voltage limit.

As avionic said, the 2sc945 is a good replacement for the 2sc458. In my opinion, the 2sc945 is under-appreciated. Although the 2sc945 is not advertised as a low noise transistor, the noise performance of the 2sc945 is better than many so called "low noise transistors"
 
oldvinyldude said:
Thanks for the batch number clarification ecluser and avionic.

I have bought a supply of KSC1845’s, as a few threads with cross references for subs, suggested they are correct.

Should I get the 1815’s instead?
Click to expand...
Good morning, where did you buy the ksc1845 transistor? I want to exchange the 2sc458 for the ksc1845, my device is an Akai gx-747, I can't find this transistor here in Brazil, thank you
 
Is that exactly the one in the photo?
 

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Juva said:
Which of these should I buy?
Click to expand...

Start with the transistor you are going to replace. What is its pinout? It will be EBC or ECB or BCE.

If it has either ECB or BCE pinout, then you want a replacement device with a center collector (the middle or center pin of its three legs is the collector). That would be the KSC945C.

If, instead, the transistor you are replacing has a EBC pinout, so its collector is on one end of the device instead of in the middle, then you want the non-center-collector version of the KSC945 (so the one without the C at the end of the model name).
 
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