Kenwood KA-94 worth fixing?

flexxmi · Jul 2, 2018

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.

kanewolf · Jul 2, 2018

They have sold on E-Bay for $70. Any repair will probably cost that much. Is it worth that to you? Service manual sold for $13 on E-Bay, but there are none listed right now.

americanaudiophile · Jul 2, 2018

Most likely cause of the fuse blowing would be bad power supply or blown channel. Either way the unit isn't remotely worth investing in the repair. Even the parts might be more than the unit is worth and if you have to pay for labor forget about it.
If you want to the schematic and service manual you can get it for free
https://www.hifiengine.com/manual_library/kenwood/ka-94.shtml

flexxmi · Jul 2, 2018

americanaudiophile :

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 · Jul 3, 2018

Thank you for the link.

americanaudiophile · Jul 3, 2018

A chip amp can be tricky to remove but a discreet amp needs more diagnosis. Check the price of the output transistors. That will give you an idea of possible parts cost.

flexxmi · Jul 5, 2018

americanaudiophile :

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 · Jul 12, 2018

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?

americanaudiophile · Jul 12, 2018

Those are a PNP-NPN pair. I doubt they would have been matched when the amp was made so you probably only need to replace the actual transistor that is bad. If the other channel is fine then leave them completely alone.

flexxmi · Nov 4, 2018

americanaudiophile :

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 · Nov 16, 2018

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 · Jan 8, 2019

americanaudiophile :

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?

jsmithepa · Jan 9, 2019

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 · Jan 10, 2019

jsmithepa :

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.

flexxmi · Feb 6, 2019

So this unit powers up, but I hear no relay protect click like most units do when they're powered up. Can someone please help me get this unit functioning again?

flexxmi · Feb 17, 2019

Here's a link to the issues. Somehow my post got closed before the issue was resolved. I've made one repair and the unit powers up now, the front is illuminating and it's not blowing fuses but I get no power relay 'click' when the unit is powered up and there is no audio. Can someone please guide me as to what my next step should be? I have the schematic already - just need some direction. There's obviously something else wrong that needs to be fixed. No bulging capacitors, nothing obvious stands out as looking like it's fried, but something is keeping this unit from working as it should. Thanks in advance for your knowledgeable guidance.