Kenwood Ka6000

[Dart07]

hello, I have a request for diagnostic tips
I bought a Ka6000 in a nice visual condition and technically unknown. After initial inspection everything looks original and there are no signs of repair, fuses ok. First start-up through the bulb, literally for 1 second because the bulb did not go out and shines strongly so short circuit... where to start looking? Which circuit to start with? I am an amateur in the subject but I have already revived several devices with simple faults.

Thanks in advance for your help
Artur

 

[mrk229]

Greetings and welcome.

Kudos to you for not just plugging it in. You checked under the hood and used a DBT

One of the most common causes for that type of issue is a shorted output transistor or transistors.
You sir are lucky in that the 6000 has an easy way to isolate the amplifier output sections from the power supply.

Simply remove Plug "A" and test with the DBT again. If the problem is in the amp outputs the bulb will not go bright.
If it does go bright then the issue is probably in the power supply section.

 

[Dart07]

Great, thank you very much mrk229 for this tip.
I'll start with that and it will make the next steps much easier. I was already looking for MJ21194G just in case...
Regards

 

[Semanon]

Congrats on the KA-6000. It is a fine amp. Keep us posted on the progress. Pix always help future thread readers.

Once it’s up and running, let us know your thoughts on the sound. There are quite a few fans of that amp.

 

[Dart07]

Of course, but I haven't gotten around to it yet. I'm also a fan of these series, I also have 5002 and 7002 and this one will complete the collection.

 

[Dart07]

Of course, but I haven't gotten around to it yet. I'm also a fan of these series, I also have 5002 and 7002 and this one will complete the collection.

hello, slowly getting back to the topic... today I opened the kt7000 pd tuner set because it wasn't working either and such a surprise.... what is it? oil from the transformer because it leaked right under it? no traces of flooding from the top, clean.

 

[VHAALNPATTET]

I have a kt7000 also I recently purchased with similar coloration. Oddly enough it's on the same filler capacitor. I have been trying to replace the thing but really struggled on it. AEverything on board is super close and difficult so I screwed up the FM board somehow. For now I just set aside trying to figure out if I want to just swap out a used FM board I have and until the tuner doesn't work just leave it be or do I want to roll up the selves and go for it.

Anyways hoping you get a reply with some suggestions. Sorry can't help as I am also learning

 

[Dart07]

Update...
the transformer in kt7000 is damaged and I am looking for a working or new replacement. Please advise from other model it may fit?

 

[Dart07]

Great, thank you very much mrk229 for this tip.
I'll start with that and it will make the next steps much easier. I was already looking for MJ21194G just in case...
Regards

transistors are ok, I took them out and measured... it was definitely hot at the tip, the wire insulation melted but the transistors survived

 

[Dart07]

Greetings and welcome.

Kudos to you for not just plugging it in. You checked under the hood and used a DBT

One of the most common causes for that type of issue is a shorted output transistor or transistors.
You sir are lucky in that the 6000 has an easy way to isolate the amplifier output sections from the power supply.

Simply remove Plug "A" and test with the DBT again. If the problem is in the amp outputs the bulb will not go bright.
If it does go bright then the issue is probably in the power supply section.


View attachment 3407626

after removing the jumper and turning it on, the bulb is still on..., all fuses ok, transformer resistance measurement on 11ohm plug, primary winding ok? surely someone has already been here because the 2sc898 transistors are from a different series and the resistors on the burnt-in side are different... here you can see "combinations" in the left channel ...
what should I check next...

 

[Semanon]

Then the next step is the power supply. Transformer secondary voltage, and diodes, main filter caps.

 

[mrk229]

Then the next step is the power supply. Transformer secondary voltage, and diodes, main filter caps.

Yep I would start with the diodes and the main filter. Diodes are D1 through D4 on a terminal strip just behind the transformer bell. The large diameter cap is the main filter.


Wow that is a serious meltdown. I would follow those wires all the way to the other end and confirm they are not melted and shorting against something.
Very surprised the transistor is good, unless the heat was from some external source? Once you get the amp sorted it would be a good idea to repair or replace the wires.

 

[Dart07]

Wow that is a serious meltdown. I would follow those wires all the way to the other end and confirm they are not melted and shorting against something.
Very surprised the transistor is good, unless the heat was from some external source? Once you get the amp sorted it would be a good idea to repair or replace the wires.

replacement without a doubt, burnt only at the ends, fortunately they didn't short-circuit anywhere... as soon as I find the basic problem I will replace them all one by one,
here is a broken capacitor on fuse 4A, but it probably doesn't cause any problems

 

[Semanon]

It will over time. I’ve never see that before on a cap.

To me that points to the need for a careful inspection of all the boards and solder joints to see if there is any other weird stuff going on. It may be nice visually, but it seems like it was driven hard at some point.

 

[mrk229]

replacement without a doubt, burnt only at the ends, fortunately they didn't short-circuit anywhere... as soon as I find the basic problem I will replace them all one by one

You can quickly check the diodes in circuit, if any are shorted it will show up.

 

[mrk229]

replacement without a doubt, burnt only at the ends, fortunately they didn't short-circuit anywhere... as soon as I find the basic problem I will replace them all one by one,
here is a broken capacitor on fuse 4A, but it probably doesn't cause any problems

Is that 4A the main power fuse? That cap is across the power line if it is C305.

If indeed it is C305 disconnect one end and power it up on the Dim Bulb again.

And if you replace it (looks like you should no matter what) be sure to get an AC line rated safety cap for it.

 

[Dart07]

do you mean replacing the C305 (for example 0.01uF X2 275V ) or using something elsein addition ?

Is that 4A the main power fuse? That cap is across the power line if it is C305.

If indeed it is C305 disconnect one end and power it up on the Dim Bulb again.

And if you replace it (looks like you should no matter what) be sure to get an AC line rated safety cap for it.

View attachment 3494614

 

[mrk229]

I mean replacing it. For a capacitor going across the AC line or connecting the chassis to the neutral side of the AC (known as death caps) they have special caps that are designed to fail open.

Safety Capacitors First: Class-X and Class-Y Capacitors - Technical Articles

Learn about Class-X and Class-Y capacitors, where they are used, and why they are referred to as

www.allaboutcircuits.com

https://www.mouser.com/c/passive-components/capacitors/safety-capacitors/

 

[Dart07]

Yep I would start with the diodes and the main filter. Diodes are D1 through D4 on a terminal strip just behind the transformer bell. The large diameter cap is the main filter.


Wow that is a serious meltdown. I would follow those wires all the way to the other end and confirm they are not melted and shorting against something.
Very surprised the transistor is good, unless the heat was from some external source? Once you get the amp sorted it would be a good idea to repair or replace the wires.


View attachment 3494553

Diodes D1-D4 are ok, capacitors checked in the circuit are also conducting, cap C305 new, tested elements work. The bulb still does not go out, jumper "A" and pre out- main in disconnected. What's next?

 

[mrk229]

Diodes D1-D4 are ok, capacitors checked in the circuit are also conducting, cap C305 new, tested elements work. The bulb still does not go out, jumper "A" and pre out- main in disconnected. What's next?

What wattage is the bulb in your DBT?