GM300 - Replacement Brain ?

In my experience modifying ex-commercial radio gear  for ham use is a mixed bag:

• The Tait 500 was poor when converted to 6m due to powerline interference when mobile
• I have a brand new VHF Motorola GM328 tuned to 2m which appears to suffer interference from broadcast band FM (pcb inductors in a tuned circuit with varactor tuning means low Q so broadband front end with no selectivity).
• Unilab's have been very good
• The Philips PRM80 converted to 2m is perhaps the best mobile radio I have had with regard to coping with pagers. 

Mind you, the Icom and Yaseu mobile rigs I own have been sadly lacking.

So when I opened a Mororla GM300 I was pleasantly surprised to see a radio with shielding over every coil in the receiver front end and a diode mixer. This was a departure from the norm and worth investigation. 

Alas, trying to reprogram the radio for 70cm use was fruitless. After a couple of hours trying every serial interface I had and several versions of the Motorala software I had no success.

Which got me thinking. It's a fairly standard PLL circuit. So I pulled the entire synthesizer/receiver/exciter board from the radio. Powered from the bench using STM8 eForth and a $1 minimal development board I quickly had the PLL loaded up.

Only problem was the oscillators would not lock up oin the required frequencies. Padding with a few surface mount caps was partially successful. The tuning range is only just wide enough.

At this point I have a proof of concept. Driving the LED display on the head looks straightforward. But I am hampered by only having a partial circuit of the radio. If you can help me it would be appreciated. 

73's