IC-735

I purchased the IC-735 back in the 80’s, it has always been a favourite rig of mine and has spent most of its life as the prime mover for my 50, 144 and 432 Mhz transverters. I retired the rig a few years back when I got the TS-2000 but recently resurrected it after my son, Kristian, 2E0KGG, obtained his licence.

After bringing the rig out of retirement I found it had three small faults that required attention. Two of the dial lamps had unfortunately failed, the AF-gain control was very noisy and the VFO was slightly off frequency.

None of this really worried me, I thought I’d simply source a new AF/RF control, some LEDs for the display and fix all three “issues” in one hit. After much research it would seem that the AF/RF twin POT is no longer available, so I was left to hope that a good spray of switch cleaner / lubricant would do the job!

I read many articles describing replacing blown bulbs with LEDs and by using different colour LEDs the rig could be given a completely new look! I also discovered that the four small bulbs used to illuminate the front panel on the IC-735 each had a small plastic “hood” to give the characteristic green display. One of the sites I visited had a photo of an IC-735 that had been fitted with “white” LEDs and it looked really good, so I decided that I would do the same.

These four photos show the location of each of the original bulbs. It was fairly easy with a small soldering iron and tweezers to remove them. By carefully studying the track layout and double checking with a meter I knew the +ve supply rail. Each bulb was replaced by a “white” LED and series resistor. I experimented with a number of different value resistors to get the desired brightness. Note that the “dial lamp brightness” pot accessed from the side of the rig didn’t provide much adjustment. Unfortunately I do not know the specification of the LEDs used as they were once again from the “spares box”.

Once all four LEDs were in place and everything checked I gave the AF/RF POT a spray of cleaner / lubricant and left it overnight. The next morning I gave it another spray of cleaner and then set about the frequency adjustment. Fortunately ICOM made this a fairly easy adjustment and it’s well documented in the manual.

There was just one thing that wasn’t expected…

I knew about the green coloured “boots” on each bulb and I had definately removed all four bulbs plus “boots” and replaced the bulbs with four “white” LEDs all from the same un-opened pack yet the meter illumination still had a yellow / green tint! This was not apparent in the photos I’d seen previously and I could not see any obvious colouring to the meter casing…

At the end of the day I don’t find it a big issue, everything is working fine, the rig is performing very well, and it’s also interesting to see if any visitors to the shack ask about the difference…  🙂

This photo was taken in poor light with a phone camera, so the display does appear rather bright on the outer edges. I have since read that rubbing the surface of each LED with abrasive paper can help diffuse the light, so maybe next time I have the covers off I might be tempted to have another go (and change back to green?  🙂  )

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