I got it from a fellow Spanish ham in September 2010. It was depicted as unworking, with repeated visits to the Technical Service. It seemed as there was some hidden problem which caused the rig to blew up again.
As I enjoy challenges, I bought it at a good price and started working... keep reading to know what I found!
The MarkV was in good physical shape, with just some scratches in the covers here and there. But front panel was close to perfect... read on and you will find why!
It worked on transmission but received signals attenuated a lot of dBs (50 or so)
I knew unit didn't receive at that moment, so I looked for the usual suspect, a PIN diode which has the tendency to fail. And, yes, it was faulty:
It had been already replaced, as I suspected, so it was at least second time it failed... not good!. I put a BAR64-03W as a replacement. I have found these diodes work nicely:
As that diode is the first to die, but it could be not the only one, I checked all bandpass filters below that board:
And replaced quite a lot of them!:
I also found an already replaced Ge 1N60 diode. The replacemebt was Si so I put the real one:
Once these repairs were done, rig received beautifully :-). But I was afraid there should be something wrong in the TX section, as I had been told that unit didn't keep working for long in previous repairs. So I went to check the TX section... and found interesting things.
This is the final amplifier board:
Final transistors had been replaced but work seemed OK:
BUT, LOOK AT THIS!!!
YES, there is tape all along the ventilation holes!!!. Of course, I removed it and routed the cables over the metal cover, as Yaesu intended!
I rechecked bias (they were a bit off) and tried transmission... it worked but there was some relay clicking noise when operating on 40m and below, even at reduced power and on a dummy load. It followed voice modulation so something was definitely wrong...
I removed the Automatic Tuner cover, as it hosts also RX/TX relays and antenna selection. And then I found more obviously already repaired areas:
Then another surprise arised. I found that the PROC button LED didn't work (but PROC function did), so I dismantled the front panel to arrive to it. It was quite a job!
Someone had been there before, as the pen markings on the connectors revealed... why?
During the disassembly process, I found the cause of the close to mint front panel... it had been replaced!. How do I know?. Because the keypad PCB was broken in two, glued and bridged!
In order to break that PCB, tuning knob should be pushed into the unit. And it is impossible if front panel does not break...
So I finally got to the PROC button PCB:
And found that the LED on it had a broken leg:
This is a general view of the skeleton of the front panel:
People is not so careful as I am when working with delicate parts, as this scratch I found on the display modules shows :-(
Of course, I had not an spare PCB to replace the glued one, so I put everything back on its place. Now I had PROC light and a better looking display (due to the careful cleaning of all the surfaces):
I replaced all non-standard components with suitable ones. There was a big goof with the replaced control power transistor (large black unit in the picture), as it required lots more driving than the original one.
The TX switching diode was in the opposite side of the PCB and was not the original type... but I checked the datasheet and it seemed suitable. As I had no a replacement on hand, I left it but soldering it at the correct side:
Another thing I found is that reed relay, which routes antenna signal to the RX section, was also a sub:
And, unlike the original unit, it had not its case connected to ground, as pinout had been butchered... so I added a ground pin to the case and put it back on the PCB:
But problem persisted and when transmitting 10 or more Wats on 160m, even on a dummy load, activated the RX relay, so TX signal was routed to the RX section!!!. That was for sure the root cause for the repetitive failures as, in other bands, it only happened from time to time, depending on power and antenna SWR.
I was close to the problem, but checked all and every component and all was fine :-(
I placed an order with Yaesu UK (what a great service they are!) as they had the keypad PCB, the original reed relay and the switching diode on stock. And then patiently waited for the parts to arrive...
Once I got the material, I replaced front panel keypad circuit. Here you can see part of the procedure:
As you can see, there were lots of parts involved to do that, but I didn't want to have a glued PCB waiting to fail when spares are not longer available!
Once this was done, I got into the Antenna Tuner area again and replaced all the non-original parts. I did it one by one to find which was the culprit... and it was the diode!. When I replaced it with the Yaesu specified part (U15J), problem was gone!. I set the unit for full power (200W) and even then, reed relay was quiet. Live to learn!