Kenwood KA-94 worth fixing?

flexxmi

Commendable
Nov 7, 2016
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1,580
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I have a Kenwood KA-94 that blows the fuse as soon as it is powered up. From what I've read these are nice little amps and this one has a phono input on it so I'd like to save it if it's salvageable. I have opened the unit and don't see anything outwardly apparent that is wrong - no bulging capacitors or burnt resistors. I will need someone who is familiar with these units to gently guide me along. I have no schematic for this unit either, so I suppose that would help too. Thanks in advance for any advice/help. You guys and gals have helped save two of my amps already so I'm here again hoping for some positive results.
 

flexxmi

Commendable
Nov 7, 2016
30
0
1,580
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I can do the labor - I replaced a 26 pin chip in the last amp I fixed and it's still working great. The chip was a mere $8 shipped free from Japan. I have the equipment needed to do repairs, just thought I would see how labor intense and costly this job would be. Thought maybe I could save the old gal but it's sounding like you guys think she'd be more bother than worth.
 

flexxmi

Commendable
Nov 7, 2016
30
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1,580
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Thanks. I am checking them out now but I have a question. The 2SA1215 & 2SC2921 are sold in pairs. They also have a number below the part number. The pair I see for sale has 280 below the part number, while the number on all four of the ones in my amp is 4D0. Is this number significant or does it simply imply a matching set? I have yet to check them with the VO meter to see if any are bad, but if I have a bad one will I have to replace all four with matching numbers? I appreciate your help.
 

flexxmi

Commendable
Nov 7, 2016
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Maybe I need to be a little more specific. There are two pair of this transistor in this unit - 1 each of the 2SA1215 & 2SC2921 for each channel) and all of the lower numbers are matching (4D0). If only one is bad will I need to replace all four with matching lower numbers?
 

flexxmi

Commendable
Nov 7, 2016
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When these are metered I am assuming that the readings for the chips for one side of the amp should read the same as the other but one side is giving high readings while the other is not. Is this an indicator that there is the possibility of a bad zener in the circuit for that side? I am taking readings from the three posts on the chips so I'm pretty sure the chips on the outside are bad but should I look further for something more that may have caused these to blow or is this a pretty common problem that these chips just blow after awhile?
 

flexxmi

Commendable
Nov 7, 2016
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The original fuse was not in the block and I want to make sure I'm reading this right. Do I need a 250v 3A fuse for this unit? Should I get fast blow or slow blow? Are these 6mm x 30mm fuses? Thank you for any help you can provide.
 

flexxmi

Commendable
Nov 7, 2016
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1,580
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I have successfully identified and replaced two bad power transistors. The unit now powered up and the fuse didn't blow, but I have no sound. No sound from the headphone jack either.

Suggestions?
 
Both channels dead simultaneously?

I guess I would check all power rails present, that's easy enough with a DMM. Then amps are just a series of amplifier stages, buffers etc, trace it, would be easier with an oscilloscope.
 

flexxmi

Commendable
Nov 7, 2016
30
0
1,580
0


Forgive me, I am a newb and still very much learning. What is a DMM? And these power rails you speak of - do you check them with the power off and the unit unplugged? I don't have an oscilloscope and have never used one. All I own is a VOM. I can do the work but I will need a lot of help identifying the issue.
 
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