A priori: Click on images in this post to enlarge in new tabs.

“Going back in time on the sound of the nation it’s a flash back back back … ”
Listen here to this popular jingle from the 70′s .

For whatever reason I’m in a repair mood lately. I got fed up looking at equipment
‘to be repaired’ but never did. Sometimes hobby is similar to work. You’ve to do
things which are dreadful. But these dreadful things have to be done by someone (me).

What is the issue. I own two IC-402′s of which one became defect around 7 years ago.

Say what? IC-402? Are you nuts? Well . . . yes and no. However, bear in mind these
old fashioned IC-402′s deliver our VHF/UHF/SHF contest team victories since >30 years.

First, let me post some pictures. Below left is a picture taken during the March 2008 contest.
IUD (Icom Under Discussion) is located on the right, at that time apparently working.
The left IC-402 is owned by my friend Ron PA3BPC / DL3BPC.

Below right is a picture I took around one hour ago, trying to win the RigPix contest ; -)

Left: 2x IC-402 active during a 70cm contest, right: IUD on my workbench.

Our contest team won innumerous 70cm contests with IC-402′s as driver and receivers.
This neat little rig sounds immaculate due to its remarkable low LO phase noise.
Yes, we tried other transceivers but everytime we went back to the good old IC-402′s.

And yes, these rigs are over 40 years of age. But . . . still outperform modern transceivers.
Our ‘last resort’ argument over the last 30 years towards sceptic persons is:

“If your transceiver is better than our IC-402, why don’t you win contests?”

100% of the time the sceptic remains silent (because he didn’t win nor does he own IC-402′s ; -).
Therefore, the proof of the pudding is in the eating. IC-402′s taste very well!

Oh yes, one secret is revealed now.
I modified the MF strip of my IC-402′s according to this document.

The issue.
I could hear noise, but that was all. Both RX and TX didn’t work.

Now . . . where to start. Look (and click!) on the images below.

Have you studied the enlarged pictures above? If yes . . . it’s a mess (which rhymes ; -)
But, this is ‘how it was done’ in the 70′s. At that time state of the art. In 2016 we frown our eyebrows.

Again, where to ‘start’? Well, first thing -after a ‘non power up failure’- is to
ascertain if all ‘frequencies’ inside a transceiver are present. After connecting a counter to CP2
it appeared the ‘band’ (crystal) LO worked fine (Google on the IC-402 manual to find out).

Next IUI (Item Under Investigation) was the VXO. My counter had some difficulties measuring the
VXO frequency. Tentative outcome was around 47 MHz, so it seemed to work fine.

Sometimes you need a little luck. My efforts to measure the VXO frequency caused suspicion.

Using an Ohm-meter the resistance across the VXO terminals appeared to be (close to) 0Ω.

Looking at the IC-402 circuit diagram this was weird. Could there be a shortcut? If yes, where?

Lets look at the relevant part of the circuit diagram below.

It appeared that the thin coax cable from the VXO to the 2nd mixer was shortcutted indeed.
However, in order to ascertain where, or to replace the cable would be a horrendous job!

With lots of fast movements I was able to dismount the thin coax from the mixer module.
Because the D1 and D2 cathodes connect AND face upwards it would be relatively simple to
connect a (new) VXO cable. Measuring these cathodes (D1, D2) revealed no shortcut towards GND.

I also disconnected the connector at the VXO side.
When I tried to pull out the small thin cable for inspection it was ‘firmly’ stuck.

Like I said, sometimes you need some luck when repairing equipment.
It seemed the VXO cable was squeezed between a nut washer and the chassis!
Now . . . what is this for a defect ? This fault must have been inside this IC-402 ever since !

Below a close up picture of the solved issue.

After releasing the cable from its nut washer I fiddled a little and the shortcut disappeared.
Inspecting the cable damage with a magnifying glass revealed the cable could be rescued.

Quickly the VXO cable was resoldered and a 432 MHz signal was applied to the antenna input. Presto!

I spent some time to trim the receiver. The result was a ‘non’ Minimum Discernible Signal (MDS).
In other words, I could easily hear the lowest signal generator level (-140 dBm) from the speaker
and didn’t bother to insert an attenuator in order to measure the full Monty.

Long story short, this IC-402 works flawlessly and is ready to be used in 70cm contests : -)