MTS DOES NOT ENDORSE THE ABOVE LINKS, ANGELFIRE ADDED THIS
The most common problem is bad solder connections in the PLL unit and Display driver unit.
BRIEF History: The 211/701 came out in 1976 (give or take a few months), Japan was trying a new type of PCB, with plated thru holes, it didn't work very well so the plated thru holes were replace with pins, these pins were coated to bond with copper and solder, and it almost worked, these pins are breaking down now, and can cause anything from open connections to low resistive connections. What we are calling updates, are to remove these pins and replace them with copper wire bent over on top and bottom, then resolder the connection. It is important to remove all the old solder. The better method is to add jumper wires on the bottom side of the board (this is what we do, more reliable), I will try to post some pictures of where the wires go, it will take a while though. The 701 only has a few pins, and most of the boards stayed with the platted thru holes. The 211 had 4 generations of PLL's and 3 genrations of Display drivers. The 245 uses the same PLL, and had 2 generations of Display drivers.
211 PLL Alignment: The PLL alignment is straight forward, does require a accurate frequency counter and patience. If the frequency is off by more than 4Khz, there are other problems and the alignment sheets won't help. Most common causes of problems are bad solder joints, dried out caps (electrolytics) and the -9v regulator's (DC/DC converter) associated parts. (it is very rare for the -9v reg. (DP1) to fail!). Align A, Align B
701 Alignment Is coverd in the rear of the owners manual.
PLL Updates This is a picture of updating (wiring) a mid production version PLL (400Kb)211 PLL, and this is the older version (200Kb)211 PLL Older Version, and this is the newer version normally called the black board (200Kb) 211 PLL Newer version, there is one version newer than this, but it was a version that came out after the production stopped, it was a service upgrade, there are very few of these versions out there and once installed, I am not aware of any problems. I will try to find a picture of it and post it.
The RM-2 Is a Computer controller for the 701/211/245. IT allows direct frequency entry (not bad for 1978), DTMF pad, 4 Memory channels, and control for scanning (some radio's need a mod for scan stop), offset and Dup functions. Fairly reliable unit. MOST IMPORTANT; turn the RM2 on LAST and off FIRST, just turning off radio power can damage the RM2 when power is turned back on. Most common symptom is 0 _ _ 0 or 0 in the display, most common cause IC2 and IC11.
211 / 251 PL encoder
We are asked allot about putting in a PL into the 211 or 251A. Yes it can be done. Communications Specialists (800-854-0547) have a internal encoder unit and a external encoder unit. The int. unit runs about $30 and the external about $50. The internal is programed by a dip switch and will fit neatly under the top hatch cover. Good choice if one or two tones is all that is needed. If you use more tones, I recommend the external unit, it has a rotary selector that gives you quick access to all the sub tones used. This is a sheet showing where to connect the tone wires. PL Install (200Kb)
HF finals are usually very reliable, barring Mother Nature. If you measure the voltage on the base, radio off, power applied, it should be 0 (0.05 max, works for the drivers too, but the radio needs to be on) The 701 had three different finals, 2SC2097 (80W device), 2SC2097H (100W device) and the main stay 2SC2097HH (140W device). I have tried to find another source for the HH version, but ICOM is it, and those days are probably numbered. You can use the "H" version, but I recommend (strongly) setting the ALC to 80W. Each version has a different bias, output capacitance configuration. DO NOT USE A 701PS! it is unregulated, the regulator is in the 701 via the power connector and is capable of 28v!
The 251 is basically a more advanced version of the 211. The Main unit is almost the same. The PLL and Logic are very different. The biggest issue with the 251 is the CMOS logic. It "glitches" and is very static sensitive. The CPU and Expander are no longer available new. Generally it is very reliable, and needs very little maintenance.
451 The 451 came in 2 different versions 430-439.99 or 440 to 449.99. Not possible to make a 20mhz radio of it. (that is why the 471 was so popular). No real issues. same CMOS logic as the 251, but for some reason, never really had any problems with it. Alignment is rarely needed, and you need a good accurate counter.