An Icom IC-260A story by Ramon Reyes DU1FV

An Icom IC-260A story by Ramon Reyes DU1FV

I was helping Ferry DV1FA find a good vhf sideband rig. After checking out ebay and some local offerings. I found that another old friend was selling an old vhf sidebander. 
Later it turns out he has two old ones. One was a Kenwood TR-9000, the other an Icom IC-260A. Both are ealry 80's vintage!

Well the Kenwood went to Ferry as it was the only one working. The other, an icom looked nice from the photos considering its vintage. but had several things wrong with it.
Ferry tested the icom and found when it did power up properly on 145.000 (normally after several power on, power off cycles) it did receive and transmit well. This made the Icom very tempting. As luck would have it, I got a chance to talk to the radios' owner.

After some haggling I was able to negotiate a good (I think) "as is' price for it.

Off to the workbench!

Problems found.

1. The cpu wont reset properly. The cpu reset capacitor was found and changed to a tantalum type.

2. The vfo tuned only upwards regardless of knob turn direction. With the aid of my old dual trace scope, I found a bad cmos 4013 flip flop chip in the circuits past the photo-diode chopper (output was permanently high). In order to minimize risk of damaging the double sided phenolic board, I opted to cut up the old chip in board with a wire cutter. One needs eye protection for this job as bits of hard plastic from the disintegrating chip fly about uncontrollably. I then desoldered the reamining i.c. pins individually, with a pump. I soldered in a 14pin hi rel (as in high reliability?) socket to accept the new 4013 flip flop. I did not expect the chip to be raised that high above the board by the socket but fortunately the cover still went on without a problem.

3. Squelch on FM mode not working well. I suspected and confirmed the noise charging capacitor was leaky. It was changed to new tantalum unit.

4. At this point, I tried testing the transmit on ssb using another rig to monitor the signal. I found it odd that the received audio was distorted. If one spoke softly into the mic, there was almost no output to be heard on the monitor but speak steadily louder and louder and audio level on the monitor will suddenly jump up but still sounded distorted. It sounded as if the transmission was not linear. So I peeked into the PA section and lo and behold! I found that an SC-1019 (a 25w fm final module) has been installed on this all mode radio! The SC-1019 was ok for FM transmitting but sounded horrible when used for transmitting ssb. Perhaps when the original module died, there was no stock in Manila, so they put in an FM type. as the radio was used for FM mainly, anyway.

Luckily for me, I found a source in Manila that had a proper VHF SSB (class AB) module.

5. When I got the rig it was permanently wired for hi power . I needed a hi and low power switch so I restored the original wiring for power control. The tech who worked on the rig previously had used the hi low sw and made it into the power switch of the radio . This is probably because, the original power switch at the volume control went bad.

6. I tried inserting a CW key into the jack in back of the rig and found it did not work. I dismantled the small cover and found some wiring changes had been made. I then restored the cw key wiring as well as the speaker jack wiring as well (speaker jack was jumpered).

7. I needed a power switch and took a look at the Memory switch at the back. (You have to remember that this radio was made in the early days of computers and that memory circuits were power hogs. There were no cmos based memories that could be kept alive by a siver oxide cell.) It was a simple matter to rewire the "memory backup switch" as the new power switch. As long as the rig was connected to an operating power supply memory was retained and even if the rig was powered off by this new switch.

After adjusting the low and hi power trimmers and the rf driver trimmer capacitor, the Ic-260A seems to be working to spec already!

What is probably left to do is to get a good counter to calibrate the frequencies. But that could wait!

In hindsight, probably the apparently "serious" nature of the defects was what kept the unit in storage for a good many years which in turn accounts for its lightly used appearance, externally and internally. I remember something ol' George (Serapio) ex DU1SQ would say: "Yes, it may be a lemon but some lemons are sweet!"


73

Ramon Reyes DU1FV

Update sometime March. 2013

Whenever I went to Raon (Manila's Electronic district) I would always be on the look out for a proper power on switch/volume control. I onve saw a promising part in a bin of junk at an electronics store and decided to buy that.  Upon reaching home however, I found that it would not fit all. Weeks later I tried a search on ebay for pots with switches and found a pot with switch used in electric guitars.  The product was from China. I thought I'd take a gamble and ordered it.  The part came in after three weeks or so.

 Studying the schematic , I found the volume was actually electronic. It controlled a voltage that went into this special IC that was the actual voume control,   I did not have an exact pot value match but made things good by adding a fixed resistor.  So now the rig is trurned off by pulling on the voume and turned on by pushing it in.  It would have been ideal if it were like Kenwood's TR-9130  which had a  push once to turn on and push once again to turn off, volume control, But tje mod I tooka gamble on, worked  just fine. By the way when I got the radio, the volume was not the original and they had uysed the low /high power switch as the power switch. I suspect that  power-on  motion worn down part of the carbon lining of the volume. Tthis was one of those standard " turn all the way counter clockwise" to turn off, This has always been a faiiure mechanisim of many radios, even receivers.  So when I look to buy a radio receiver, I prefer ones whose power switch is separate from the volume control.  The present push on and push off system does not harm the carbon lining of the volume pot.  Now the rig is alsmost like mint.HIHI.


Update September 2013

I received an email regarding  the mentioned squelch circuit repair from Dana, KD0UTH so I looked up the complete schematic I now decided to patiently paste (elecronically) together the several pages of partial schematics available on the web at that time. You know how it can be hard using split page schematics. Some of the original pages were not perfectly scanned and there are small problems with the alignment. Then again, using this "pasted together" schematic is  better than trying to make sense of a diagram while switching from one page to another (which gave me a headache, previously.)

 The ic-260a has two squelch controls ganged togeter , one for FM and another for sideband.  We note that half of IC5 AN829 is part of the FM SQL ckt.  

If we look at the complete schematic below we find that pertinent half of IC5 drawn right below the FM IF chip, IC 4.  Following the amp's output pin we find that right after the two voltage doubler diodes is charging capacitor C52.  It has probablly gone leaky after all these yeare and that it should be replaced with a tantalum of the same value. Kindly be careful with polarity. I suggest marking the board with a plus sign written on a piece of masking tape, and take care with following the tantalum cap polarity marks as well. Some tantalums mark the negative with a long black strip  while others mark the positive side with a plus sign.  The complete diagram is a big file and is a bit hard to read on this web page,  

 A small closeup view of the FM sq circuit is shown here.

So, I guess that wraps up this story (for now) so folks, keep experimeniting, repairing, restoring and homebrewing!        73 DE Ramon DU1FV