Kenwood KR-V9020 Display question

ranukic

Active Member
Hey,

I picked this up for my garage and I noticed the display flashes from bright to dim. Has anyone run across this type of issue before?

Thanks,

James
 
The VFD drive circuitry and the VFD connection to its PCB will need investigation.

Can you elaborate? Is it a regular flashing or stimulated by shock to the cabinet or is it intermittent. Is the 'bright' brighter than normal or is the 'dim' darker than normal? Does it settle down or constantly flash?
 
Thanks for responding restorer-john. I uploaded a video of it that can be seen here
I thought it would make for a better explanation of the flickering. I currently am driving (4) 6 ohm outdoor 120 watt Yamaha NS-AW150 speakers and a passive sub. And I normally have the music at 3-4 so not extremely loud.

Thanks,
James
 
Hi James,

What electronics skill level do you have?

The issue is likely to be in the switching or power supply to the high voltage (-28v) to the VFD (FL display) as the entire display is fluctuating, but appears otherwise fully lit and functional. The heaters are fine.

I would start in the power supply for the VFD, including checking the FL (VFD) switching and the zener regulator as per the two schematic captures I have taken below. These are from the model 8020, but I am hoping the general parts placement is similar to yours.

Check the voltage on D24/C11 and ensure the cap and the zener are good.

vfd 01.JPG

vfd 02.JPG


On the power supply, check C163, the 47uF 63v cap- in fact, I'd just replace it as it could cause this entire problem. Check Q23 or equivalent is being switched on or off and doesn't have a fluctuating base drive to it. Check the -30v is stable on not full of ripple. (use a DMM on ACV/mV to see that or a DSO/CRO)

Assuming the main boards are the same on this model (I'm hoping) this is where c163 lives:

c163.JPG
 
Last edited:
Hi James,

What electronics skill level do you have?

The issue is likely to be in the switching or power supply to the high voltage (-28v) to the VFD (FL display) as the entire display is fluctuating, but appears otherwise fully lit and functional. The heaters are fine.

I would start in the power supply for the VFD, including checking the FL (VFD) switching and the zener regulator as per the two schematic captures I have taken below. These are from the model 8020, but I am hoping the general parts placement is similar to yours.

Check the voltage on D24/C11 and ensure the cap and the zener are good.

View attachment 1187662

View attachment 1187670


On the power supply, check C163, the 47uF 63v cap- in fact, I'd just replace it as it could cause this entire problem. Check Q23 or equivalent is being switched on or off and doesn't have a fluctuating base drive to it. Check the -30v is stable on not full of ripple. (use a DMM on ACV/mV to see that or a DSO/CRO)

Assuming the main boards are the same on this model (I'm hoping) this is where c163 lives:

View attachment 1187674
Thanks Again, I will be traveling for the next few days so I won’t get back to this for a while. I had planned on changing the caps but I will also take a look at the diodes to see if there are any burned marks on the boards. From what I have seen in the past if the diode goes it causes a short and blows the fuse. Atleast for the PS that is.

I will keep you posted

Thanks,
James
 
AE5361C8-C0A2-4D24-A0B3-0157B6271F1C.jpeg BE1F2622-C473-4F83-BCB6-8C4DBC8E9F58.jpeg E03A7A41-6D11-40A0-A48B-18C616B6F611.jpeg Hey,

So I took the cover off and peaked inside. I will need to replace several caps on the PS board. Took some photos for you to see how she was mistreated over the years.

I will let you know how it turns out.
 
Oh yes I did. I took some compressed air to it then used some deoxit and a couple different types of brushes to clean up the boards. Thank you again
 
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