First let me say, working on this radio is NOT for the faint of heart or a beginner! The components are EXTREMELY small and simply letting your torx driver slip and scrape across the board and you have probably severed a trace or removed a component or two!
The modification is similar to modifying a Maxtrac's VCO. I, however, am not a fan of the conductive ink and use thin copper tape as it is easier to move around once on the board.
I apologize in advance for the poor quality photos, but I think you will get the idea.
First, the VCO's are on the bottom of the board so they are inaccessible simply by opening the top. You will have to remove the entire board from the radio. It is not as hard as it sounds. Just remember to remove the two metal clips that hold the power and antenna connectors in place!
Just a quick operational note, we have noticed that even on MCS's that seem to work OK at 927, there is a "strange" squelch tail after a carrier drops. This is due to the VCO being so close to the edge of it's operational range. This problem goes away if you can tune the VCO up to around 1V at 927.
This modification is for the few MCS2000's that have trouble operating in the 900 HAM band due to the VCO unlocking at the bottom of the band. Before you remove the board, check the lock voltage. It can be found in the BLUR next to the arrow below. In my case, the VCO would unlock around 927.400 at 0.44V on the test point, and when it unlocked, it would read 0.73V. After the mod below, the voltage at 927.0125 was 0.57V and at 927.9875 it was 0.85V. Also note that unlike the Maxtrac, one vco is TX and one is RX instead of the usual one for RPT TX and RX and the other for TALKAROUND or SIMPLEX. We will ONLY be touching the RX VCO as I had no TX issues with my MCS.
Now, after taking a few measurements, remove the board CAREFULLY and don't forget that the PA and power and RF connectors will all come with it. Be careful of the middle section of the board as it is held in by some "grounding fingers" and trying to remove the board by prying the edges can result in the board breaking in two! Try to pull up with some type of "hook" thru the screw holes to break it free. Once it is out, peel the yellow tape off the opening to the tuning tab in the RX VCO. It resembles the VCO tuning TAB in a Maxtrac. DO NOT try to remove the tin cover!! You will have to get creative with a thin soldering iron and work thru the opening. The gold tab has a thin coating on it. Carefully remove the coating with something like a jewelers screwdriver, by scraping it until you see shiny gold.
Now, what I did was take a piece of copper tape, avail from Home Depot as an insect deterrent, and I cut a piece 1mm X 2MM, tinned one side with a very thin layer of solder and tacked it to the gold with a VERY SMALL portion of it overlapping onto the part where the gold had been etched off from the factory. I held it in place with a bamboo skewer while soldering it. As with the Maxtrac, this tab is on a ground plane so it dissipates heat very well! I had to hold my little 25W soldering iron on it for a good 10 seconds for it to adhere. I then pressed on it to make sure it was solid in place, replaced the yellow tape and reassembled the radio. Success!!!
Now test your radio and check your lock voltage.
Here's a couple images from the manual to help.
Close up of the test point.
Close up of the VCO tuning tab. This is an unmodified board that had almost NO gold removed from the factory. Probably would have worked fine on 900!! The unit on the left had about 1mm of gold removed before I added the copper to lock the VCO at 927. It is about the same size as the tab on a Maxtrac.