KA-7002 trouble

[toymanmsp]

I've recently started to refurbish my KA-7002 integrated. I've rebuilt the driver board and all was good until I got to the low level amp board. I've replaced the caps and transistors on the low level amp board, reinstalled the driver board and powered it up and the relay started clicking repeatedly until I powered down. I thought that I must have installed a transistor incorrectly and this was causing the problem, a bad solder or solder bridge. I went thru the low level amp board again and didn't see anything that was suspect and from what I can see the transistor orientation is correct along with the caps. Here's the strange thing is that after I had look at the low level amp board and reinstalled the driver board powered it up again the relay clicking has stopped but now my dbt lights up like a Christmas tree. If I remove the driver board and power up it does the same thing? I'm not sure why the dbt is lighting up when the driver board is removed.

One thing to note which may or may not be part of the issue. I tested the main filter caps which are rated at 4800 uf but my Peak Atlas is giving me a capacitance of 10240 and 10250 uf on each of the filter caps. This was done in circuit. Could this be part of the issue?

I'm at a bit of a loss any ideas or suggestions would be appreciated. She's a beautiful piece and want to get this rebuild back on track. Thanks.

 

[eizner23]

If its lighting up like xmas tree w/o the board double check ground faults on low level board by using continuity mode on your DMM

Maybe you got the power wire in the wrong spot. Did you remove the wire wraps to do your work? Whats the voltage getting to the power supply side of the low level board?

 

[toymanmsp]

If its lighting up like xmas tree w/o the board double check ground faults on low level board by using continuity mode on your DMM

Maybe you got the power wire in the wrong spot. Did you remove the wire wraps to do your work? Whats the voltage getting to the power supply side of the low level board?

Thanks for the reply. I should have time today to check the board for continuity and take another voltage measurement. There are no wire wraps on the low level board it is point to point with large solder pads. I've even back tracked my work with 4 of the lead wires removed from the low level board causes the dbt to stay lit. It's very strange, never encountered this before.

 

[dr*audio]

It sounds to me like you blew the output transistors. Check them on both channels.

 

[toymanmsp]

It sounds to me like you blew the output transistors. Check them on both channels.

ok..I'll remove and test. I'll report back what I find..thanks.

 

[toymanmsp]

ok..I'll remove and test. I'll report back what I find..thanks.

well dr*audio you were spot on. Q2&Q4 are shorted other Q1&Q3 are ok. I will be ordering a pair each of MJ21193 & MJ21194 output transistors. I'll update the string once I've installed the new outputs. Thank you for your help.

 

[dr*audio]

well dr*audio you were spot on. Q2&Q4 are shorted other Q1&Q3 are ok. I will be ordering a pair each of MJ21193 & MJ21194 output transistors. I'll update the string once I've installed the new outputs. Thank you for your help.

Also keep testing the driver transistors until you stop finding bad ones.

 

[toymanmsp]

Here is an update on the rebuild for the KA-7002. After a bit of frustration, I shelved the rebuild and finally came back to it this week. I installed the new transistors and rebuilt the main driver board and voila it's up and running. Completed the remaining boards and am planning to get into my rotation in the next day or so. Very pleased with the outcome, sounds fantastic and looks...well this one is a keeper. Thanks @dr*audio for taking the time to reply. Apologies for the late reply. I've learned with this hobby sometimes is just best to walk away for a bit and come back and start again. Happy I did.

 

[dr*audio]

Glad I could help. I love this series of Kenwood. Love the look and the sound.

 

[dstariha]

Glad I could help. I love this series of Kenwood. Love the look and the sound.

I could not agree more about this series of Kenwood. Solidly built, good looking, easy to work on, solid controls and great sound.
I drive a couple of ESS AMT1's (rebuilt) with my 7002. More than enough power but well defined at lower volumes.
Thanks for helping us keep them working.