Monday, September 11, 2017

Fixing up TS-440s rigs

I've been teaching myself HF electronics and antennas lately. I thought I'd go write down some of the things I came across whilst tinkering with this hardware.

First up - I decided to choose the Kenwood TS-440S.

It's a mid 1980's solid state rig with only a few components hidden away in custom ICs. There are some parts that you just can't buy new anymore (mostly these custom parts and stuff in the final RF amplifier section) but by and large it's all a big set of interconnected single-sided PCBs covered in cables and discrete components. There's the occasional bit of 74LS logic too.

It has some pretty clean and sensitive RX paths and TX is supposed to be very good for hours and hours of work. However, these devices are pretty old, and 30+ year electronics can have a large amount of wear and tear.

There are some pretty well known crappy issues too. One of them is the SonyBond compound used in the VCO (voltage controlled oscillator) sections - it's hydroscopic and degrades over time. This ends up throwing the VCOs way off and you end up having to clean it off of the PLL/RF boards. This is pretty well documented and although time consuming, it's not impossible to fix yourself.

I'll try to do a follow-up post with some pointers on tuning the TX path behaviour because I found a lot of really inconsistent suggestions on tuning things. The service manual is also a bit confusing at times on what voltages you should see where.

There are also issues with broken connectors and a lot of dry joints. I found a lot of dry joints in my 440s, which required a lot of tidying up.

Next up in the TODO list for me is tuning the RX sensitivity to make sure it's optimal.

So, what I found with the first rig I fixed up! I wish I had taken more photos; I'll do that soon just for demonstration purposes.

  • There were lots and lots of dry joints. Everywhere.
  • Sonybond needed cleaning up - and when you do that, you have to tune VCO1 - which is the VCO generating the primary RF frequency for first stage mixing. This is used for both transmit and receive.
  • The IF board was putting out a nice, clean 8.83MHz carrier, so that was nice.
  • The transmit path hadn't been aligned in a long while, so the waveform on the output of the RF board was splatting overly large signals (> 3v peak to peak) into the finals, and this caused the finals to get very upset.
  • .. and then ALC wasn't adjusted, so the filter board was overly aggressively asserting ALC.
  • The transmit power control was very touchy - 100% carrier level at like 5% turning of the carrier level knob. Once the transmit path on the RF board was properly aligned, the RF drive output was properly putting out around 2.5v ptp -> 3.0v ptp and ALC was re-aligned on the filter board, the finals were behaving much better and the TX power control was much more linearly controllable.
  • Then you have to re-do the finals bias level controls. Careful though, the alignment process says "turn to minimum first" before you re-bias things, but the board is mounted upside down so you may be biasing them to max. :)
I'll go into some more detail later with pictures!