I have recently modified a version of this radio for 70cm amateur band operation.
As supplied, the unit had no microphone or speaker - and appeared to have been wired for data transmission. When I initially inspected the set, I was horrified! It had a thick layer of  cigarette tar deposit all over the PCBs and internal surfaces. This was reflected in the price though, so I didn't complain! :-))

I started off by dismantling the set completely, and cleaning everything (including the PCBs with all the components in situ) with a small artist's paint-brush and neat car screen-washer fluid (Isopropyl Alcohol & soap?). This was brushed in, around and under every component and left to soak for a few minutes. I then rinsed everything thoroughly with clean warm water. Each item (the PCBs and chassis mouldings) were then stacked up like toast on top the Rayburn (thetas a big range-like kitchen stove for the uneducated!) to dry. This took SEVERAL hours! The result was spotless boards with all traces of tar removed, Yipee! I just had to worry whether the thing would work after this...?
I dispensed with all the tone-control PCBs  (housed under the upper cover) and associated wiring, the 6-channel switch (I wanted more!), and the PCB mounted volume control. This allows a re-design of the front panel.

The Synthesizer in this rig is usually controlled by a 6116(?) PROM, the original channel switch addresses a few lines to select the programming information for the PLL (an 8-bit word is all that is required to select the TX / RX frequency). I had also acquired a 2516 EPROM for this set giving me 100 channels, so would need to do a bit of clever work to shoe-horn this in. (The 6116 is a 16-pin device, the 2516 is a 24-pin.) I decided that I did not want thumb-wheel channel selection,
Looking at all the options to replace thumbwheels, I settled on a 2-digit 'channel' display, and 'Up' and 'Down' push-buttons. I feel this gives a reasonable trade-off in terms of ease of construction, and facilities. It should also allow easy development of scanning hardware (but as I've already blown up one prototype, this is not as easy as I first thought!....:-(        ).
The channel display also doubles to indicate PLL lock - this being taken from the original 'power on' LED on the  rig, which was controlled by the lock-line from the synth.

So far I have a working rig, with all 100 channels available via push-buttons, defaulting to channel '00' at switch-on (corresponding to RB0, my local repeater), with the option of having any channel available as a favorite preset, accessible by a single push-button (maybe I'll use this for SU20, the FM calling channel?).

One of the biggest problems I encountered was contact bounce on the 'Up' and 'Down' buttons. Initially I thought I would be able to tame this with just an RC network, but this was not the case. In the end I resorted to using a 4011 as per all the text books.
I also needed to build a microphnoe pre-amp, as these rigs were designed to have a pre-amp in the microphone. I used a 741 op-amp and also provided a dc bias supply for an electret capsule, as I felt this gave better quality than a moving coil type. (It is also smaller, and can be more easily hidden within the car somewhere, probably on the base of the sun-visor.)
The storno originally had no speaker fitted (remeber, this was used for data only), although there was space for a very small unit, about 50mm diameter, on thte front panel. I have fitted one, to make the rig self-contained, but the quality is not that good, especially in mobile environments. I will definitely fit an external speaker when the rig goes in the car.
So far I am very happy with the conversion, it has provided me with several oppourtunities to think things out in both the electrical and mechanical senses. Even though I hate panel-bashing, I'm not too dis-pleased with the front panel...!
One pleasing aspect of the rig was the power output, I can easily achieve over 25 Watts, which is a good match to it's measured sensitivity of 0.21uV for 12dB SINAD.

Tips.
I have heard that some of these rigs can suffer from poor sensitivity - due to dirt of some kind inside the front-end filter cavities. This is easy to cure, but time consuming, as you need to remove the PCB from the chassis to gain access. Mine was not a problem, but while I had it apart to clean all the tar off, I checked it anyway.
If  you want to build some logic to control the synth (like me) instead of thumb-wheels, it is quite easy to make a PCB or use stripboard and arrange for this to plug straight into the original PROM socket. From here you can pick-up all of the data lines, power, Tx/Rx switching, etc. If I get a chance, I'll show a picture of mine, so you can see what I mean.

Specifications.

Future Developments
I intend to continue developing the rig, and this will probably include :-

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