I purchased a HP 5328a counter off ebay for a decent price. It arrived a few days later and I'd say cosmetically its a 9.9/10. After putting it on the bench and turning on the unit I released it didn't have the oven based oscillator. It did have channel C option and GPIB interface. After checking channel A I was really glad to see that things were working correctly. I moved over to test channel C. All was well I thought until I noticed that the connector on channel C seems to work intermittanly. After pulling the cover off I was pleased to see the unit was very clean inside. I removed the channel C card by taking a single screw out from the rear to remove the top cover. Removing the BNC was just a simple process of removing the nut. After taking the connector apart it was tarnished quite a bit. Some cleaning and I did apply a bit of pressure. After assembly the C channel was working perfectly.
I've got a ton of emails about the adapter for the Kenwood TM-D710A. The microphone on this unit uses a digital pulse counter based on 4017 logic IC's to determine, over a single wire, which key is pressed. This same principle can be use in other projects to read a keypad, control LED's etc with on a pin or two from a microcontroller. For reference below, are the articles on the TM-710A Adapter and associated projects.
http://www.shaneburrell.com/?p=688 - Keyboard Adapter itself - This board is line powered from the microphone cable. It effectively sits between the Kenwood radio unit and Microphone. It allows you to place a keyboard in between the two to allow functionality that Kenwood never intended per say.
The theory of operation: The microprocessor in the radio head unit sends pulses to the microphone. On each pulse the line is pulled low which the microcontroller spies on via another pin attached to the pulse pin. On a scope, it's very easy to see the line being pulled low depending on the keypress. In hacking the pulses, its just a matter of seeing what key generates what pattern. In the TM-D710A adapter I used a AVR to talk to the microphone and read a standard keyboard. The One Signal Wire board design above was used to Emulate the mic controlled by the AVR.
Below is a video some Arduino code I initially developed to scan the microphone patterns driving the Kenwood Mic from the AVR. If you look at the scope this should give you a good idea how the pulse counter is working.
The TM-D710A keyboard hack was a really fun project and hit multiple stages of hack/design. The 4017 counter is a pretty neat way of reading/controlling things using on 2 pins from a micro-controller.
I've taken on yet another TS-430 and ran into an issue with whats coming off the PLL board. I traded a TS-430 I had purchased as non-working which I repaired/tuned for a unit in very nice shape cosmetically but not working. Another HAM back on the air, but now I have another TS-430 to figure out. I suspect this may be an issue with VCO signals coming to the PLL but after spending several hours getting to this point, I've put the project down for a bit to work on my workshop. Hopefully someone on a list somewhere has seen this before and I'll hear back from someone by the next time I pick this project up.