Thursday, 2 April 2015

Restoring my old FT726R

When we moved to the USA in the early 90's Roger GW5NF got the FT726R that was my primary VHF rig. It did make a trip to Gibraltar on the 1984 ZB2IQ expedition. Roger subsequently  used it with G4VXE off a car battery for Backpackers contests but had recently retired to the shack floor due to some issues. I decided it was time to rejuvenate it

First issue was that it did not work off the internal mains supply. Looking at the shorting plug on the back panel that had been used to supply 12V from the portable battery the link had not been removed, allowing 12V to be fed into the output of the internal PSU. Luckily Yaesu had foreseen this issue and fitted a fuse which had duly blown. The fuse  was replaced and the 12v wire removed from the plug and the radio lit up off its internal supply

50MHz and 432MHz receiver and transmitters worked fine but 144MHz was quiet on receive (no sign of GB3VHF) and only produced 3W on transmit. Occasionally blipping the ptt would increase the receive noise and the beacon would appear. An internet search revealed the radio is known for having a sticking relay in the 2m module which some had cured by burnishing the contacts whereas some had needed to replace the relay. Time to examine the module

Sure enough, in the quiet receive state no 9V was being supplied to the receiver chain by the relay. The relay, FBR221D012M  is no longer available  (note the available FBR221AD012M is very different). It was suggested that the contacts needed burnishing so the cover was taken off and the contacts burnished and adjusted. . This seemed to fix the problem for the time being. The transmit chain was also aligned as per the manual; a load of flux was found all over TC01 which was removed and adjusting TC01 and TC02 increased  the power to 18W which was reduced,  as per instructions to 10W maximum. The receiver was already tuned and could not be improved.  It was noted that the front end mod using a BF981 and the IF gain increase mod had previously been done, making it state of the art at the time

While the covers were off the 50MHz module was aligned. It had been noted as having a marked peak of 18W at 52.0MHz and 8W at 50.2MHz. Also the power control had limited range. 190degree setting was 0W 200degree was 4W and 210 degrees was 7W. The module was then aligned as per the manual the power output was now flat at 10W 50 to 52.5MHz but the power control was still compressed the best achievable was 190degree setting was 0W, 280degree was 5W and 10 degrees was 10W . 

The radio has been successfully restored and has now been re-integrated into Rogers shack to compliment his TS2000. It easily drives the 2m and 6m amps to full output.

No comments:

Post a Comment