Note: This site and the data it contains have been reposted from an archive of Nolan Lee's original web site by Steve Johnson.

R-1051B IF / AF Module Reliability Modification...

IF / AF Module A2 Board Parts Layout

 

One of the resistors in the IF / AF module is prone to failure from overheating. It's probably a good idea to check both of the IF / AF modules in each of your radios to verify that the Modification Work Order to correct this potential problem has been performed on them. This particular MWO was numbered for each for the following models of the R-1051 series as follows and should be marked on the MWO label on the front panel of your receiver. Even if it is, check the modules anyway. It's possible that one or both of the modules may have been swapped at a later date with ones that hadn't had the modification performed on them.

For the R-1051, it was MWO 2

For the R-1051B, it was MWO 2

For the R-1051D, it was MWO 1

The modification is a pretty simple one involving the replacement of a 100 ohm, 1/2 watt, 5% tolerance, carbon composition resistor with a 1 watt replacement of the same resistance and tolerance values. The problem resistor is located on the A2 circuit board of the module and is labeled as R37. Looking at the parts layout printed on one side of the metal cover of the module, it's in the lower left section of the A2 board to the left of transformer T5 and between C24 and R35

Removing the A2 circuit board to install the resistor isn't necessary. Clip the 1/2 watt resistor out and attach the new 1 watt one to pins 13 and 14 which are located near the ends of the original resistor as shown on the parts layout label on the module cover. Make damn sure that when you solder one lead of the replacement resistor to pin 13 that you don't accidentally position it where it could short to the case of transistor Q10. Also, try not to melt the insulation on the various wires near pin 14. A bit of additional work space can be created by simply unscrewing the long 4 inch or so screw that is used to secure one end of the module to the receiver chassis.

Your milage may vary, and May the Force Be With You....

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