Kenwood KA-127 amplifier trouble.

[MattMan]

I have a Kenwood KA-127 amplifier. It worked fine until one day i went to turn it on and the display screen did not come on. I hear it click and the little red light on the volume knob turns on, but nothing works. I have checked the fuse, but it is fine. Any idea whats wrong?

 

[MattyMatt]

Welcome to the forums!

There are a few questions I have for you:

Do you know what kind of a screen it has? I did a bit of googling and it appears that it is a VFD (Vacuum Fluorescent Display). Now, I could be wrong here, so I would need you to confirm.... If you follow the link, it may help you find the answer.

http://en.wikipedia.org/wiki/Vacuum_fluorescent_display

Now, if it is one of these, and you take the unit apart, see if you can find an area that looks like it has a burn mark or is discolored... that may tell you that its time to find a replacement. If you do not see a burn mark, then there is a possibility that the display itself could be okay, but what you would then want to do, is see how far you can trace back from the display to the main board. The image attached, I highlighted an area that is NORMAL, this is how these displays are constructed. What you are looking for would be an additional burned/discolored area.

I know this probably isn't very helpful, but think of the issue as separate areas for example:
- You know the unit can power on, I am ASSUMING (I don't like to) that you can get audio through it. That stated, the issue at this point would be limited to ONLY the display, or the circuitry that drives it. You may want to check all other functions of the unit first... it would be helpful to narrow it to only the display.

- So you start at the display - Visually look for burn marks or discoloration (they could be small spots)
- You then continue to the wire/board that is connecting the display to another board - This would be where you want to use a Multimeter and make sure the connections are good (could just be a loose solder joint).
- From there you check the driving/controlling connection to the main board - Same as above, check with a meter between the 2 places, could be another loose joint.

If all of the above check out, then you will have to dig a little deeper, find maybe a service manual with circuit diagrams and go from there.... Honestly I am not sure of a "great" way to test a VFD... but I would do a little asking around because if you can test that and get it to work, then the problem likely got a bit easier to fix.

If you have any issues, post back, and if you are able to, see if you can find a service manual for the unit, and depending on what you find, you may need some high resolution images... so dust of that digital camera

Good luck
Matt-

 

[MattMan]

Thanks for your response. As soon as I get a meter I will check it out. (Im away at college but I have one at home). The audio actually doesn't work either. Ill let you know how it turns out.
Thanks a lot,
Matt

 

[shrtrnd]

Some of those VFD (vacuum flourescent displays) operate at a high voltage, watch yourself. Google the part number on the display when you open the unit up, and find-out
what kind of display you've got. Then you can go from there.
If it IS a VFD, look for burned parts in the power supply to the display.
Good luck.

 

[Burntout]

Hello MattyMatt,
Just found this site because of my problem with my Kenwood KA-127. When you say "its time to find a replacement" are you saying another VFD or another Amp? My kenwood ka-127 has all of the above symptoms plus there is an apparent burn spot in the lower left corner of the vfd.
So I guess what I am tying to find out is if the vfd is replaceable? If so, how do you remove the vfd? Where to buy replacement components?

Thanks,
Pat

 

[nepow]

The fact that you have no audio and no display would suggest a possible problem elsewhere!! could be a power supply circuit fault or fuseable device. You could do with a schematic diagram, all dependent on your skill level of course to pin point the fault though.

 

[davenn]

The fact that you have no audio and no display would suggest a possible problem elsewhere!! could be a power supply circuit fault or fuseable device. You could do with a schematic diagram, all dependent on your skill level of course to pin point the fault though.

Exactly!!

Im not sure why there's been so much emphasis on the display when there are obviously other bigger issues to deal with.
finding why the amp doesnt work ... as suggested a PSU problem ... will probably solve the dead display as well

Burntout you need to do some searching on the www for a service manual for the unit
there are a number of sites that offer manuals for free others that have a charge.
google the make and model # of your unit

Once you have a manual with a cct diagram ( you may even just find a link to a circuit diagram) then we can help you to hopefully find the problems

cheers
Dave

 

[Burntout]

nepow & davenn, thanks for your replies. Yes a dead power supply could be the root of all evils. Please to forgive, I'm an old guy, not named after my mother, and am not very capable with circuit diagrams. I can replace parts and am learning to solder but my knowledge of electronics is sorely lacking. The amp is for my garage to keep me company while I work on my collection of non running cars.
The fuse is good, visually & with a multimeter.
And yes, when I travel I carry a towel.

 

[(*steve*)]

Never go anywhere without your towel.

My recommendation would be to take some photos of the power supply and post them here. We can probably fairly quickly determine what you need to look more closely at, or to photograph again.

The best photographs come from using natural light (i.e. no flash) either outside or near a large window (and not in direct sunlight either). Take at least one photo from directly above the board, and try to ensure that we can read anything that is written on the board.

Power supplies can have capacitors which hold a charge (between painful and deadly) long after they have been turned off, so beware of this and don't touch anything on the board until you know it's safe.

 

[morgan123]

Hey you guys,

I know this is a relatively old thread BUT I have the same exact problem with my amp.
I turn it on, I hear one click and the volume button turns on.
Other than that, nothing whatsoever. No sound, and when I connect for example the Cd player to the back (it has extra outlets on the back so you only need to plug the amp in the wall) that won't work either so I'm kind of suspecting it is the power supply.

Would you guys mind helping me? If I take pictures of the power supply?

Thanks!

 

[morgan123]

bump?