Repair of TS820 and VFO820 - adjusting variable capacitor wiper - Page 1
Forum section: electronics / rf-microwave

author: tkamiya
author_rank: Super Contributor
timestamp: April 26, 2018, 03:35:53 am
content: I have a set of TS820 and VFO820 that suffer from the same problem. Frequency jumps. I already know the issue to be the wiper contact on a variable capacitor in the VFO. I cleaned it thoroughly, lightly lubricated it, and it works fine for a while. But If I let a week pass and try again, problem is back. Does anyone have any insight into this? I can clean, oil, and retention the little grounding wiper but it doesn't seem to be a lasting solution.

author: Ghislain
author_rank: Regular Contributor
timestamp: May 10, 2018, 10:38:40 am
content: I do not own a TS-820 but came across the following post from W5RKL when doing some research related to my good old TS-830S (no longer used).Instability in the 820 can be traced 98% of the time to one of the following sources:1. Dirty VFO variable capacitor shaft to variable capacitor frame connection inside the VFO. This causes the frequency to jump wildly as you rotate the VFO knob and the digital display will also appear unstable at the same time.2. Instability in the AF AVR UNIT 9VDC supply. This typically is not a source of a "jumpy" VFO but rather the primary source of "drift" in the 820.or3. Rear 9 pin jumper between pins 8 and 9 has intermittent connection. This will produce intermittent VFO operation through vibrations such as band, mode, and function switch changes or by simply tapping on the 820.Item 1 occurs quite often over time and in dirty/dusty or smokey environments. Cleaning the variable capacitor shaft to frame connection (fork) fixes the problem in 99% of the cases.Item 2 occurs due to aging of the 9VDC supply components, primarily D5 (6 volt zener) and Q7 (2SA496Y) regulator. The VFO is powered by 9VDC from the AF AVR UNIT board. If the 9VDC supply drifts up or down in voltage, the VFO drifts up and down in frequency, it's that simple. Replacing these components will significantly reduce the amount of drift the 820 has.Item 3. If the jumper plug is not inserted properly or, in the absence of the jumper plug, a wire is not inserted properly between pins 8 and 9 on the rear 9 pin VFO socket, the VFO will work intermittently. That means the 820 can loose both receive and transmit through vibration that causes the jumper between pins 8 and 9 to be intermittent.Since you have already performed 1, I guess it is now time to start replacing some components

author: tkamiya
author_rank: Super Contributor
timestamp: May 16, 2018, 06:31:32 pm
content: Thanks.I don't have frequency instability in sense of drift. It might very well become a problem in digital mode but for voice and CW, it's quite adequate. I have always been amazed how stable Kenwood VFOs are....Also, yes, I know about that jumper plug. I have a life time supply of them. (they are becoming hard to get)I'm curious.... how do you replace that "fork"? I can't make that and it is not available as parts. I would imagine badly made "fork" would just as bad as old. A real good cleaning and use of conductive oil cleared up the issue. Amazing stuff.