IC706 MK2 G Fault

[ZL1RQ]

While out on Niue as E6RQ my trusty 706 picked this time to die.
It started clicking continuously and will not switch on. I suspect the clicking is a soft start relay or something similar. Power supply is ok and all connections are tight, internal fuse is ok.

Has any one else had this problem or can offer any ideas.

Thanks
Alan VK4WR

[ZL3ADC]

I had a IC706 MK2G and it would click if battery voltage was low. I think maybe yours is a different problem or maybe a connection to a board with high resistance giving a similar effect.
Does the display flash when you have the clicking?

[ZL1RQ]

Yes the display did flash, but now I am home it is completely dead, wont try and power up or click.

Alan

[VK4GHZ]

With the fuse OK, and having tapped a potentially sticky relay, next thing to check would be to see if the relay's switching transistor (Q591) is good/no good.

Take the cover off, and check with a multimeter, you are seeing volts on pin 12 of J621 on the PA Unit.

If volts here, Q591 is dead and/or D591 (EMF quenching diode across relay coil) is short cct.
Q591 and D591 are both on the underside, so this pin is a convenient quick check from the top side of the board.

[VK4TJ]

It will also do that, Allen, if the fingers on the connector from the front panel to the radio go dodgy. Particularly the earth connection. From memory, I think it is pretty easy to bend them out a whisker to get better contact. An eraser across the mating pins to clean the crud off wouldn't go astray, either.

I actually blew the earth out of the ribbon cable from the "dock" for the front panel to the main board (Dont ask!). A bit of hookup wire later, I was back in business. Same symptoms as you.

Good luck!

John VK4TJ

[VK3FIX]

Thanks for the information, have a 706 with a similar fault at this stage its only intermittent



73s VK3FIX

[VK4BG]

Hi Allan,

Lift up the PLL board and have a look underneath....you will probably find the tracks corroded near one of two rubber spacers...VERY common problem that causes the symptoms you mentioned.

73
Glenn
VK4BG

[ZL1RQ]

Glen,
you are spot on with what turned out to be my problem, corrosion on the board. An easy fix.

73
Alan VK4WR

[VK4BG]

G'Day Alan,

It is a very common problem with the IC706....why the corrosion forms is a bit of a mystery, but if you don't get to it early, it can be a real mess to fix. In my opinion, EVERY 706 Owner should lift that board, and have a look underneath...and probably dump that rubber spacer for something else, as I think it is part of the problem. Anyone thinking about purchasing a 706 would be well advised to also have a peep under the PLL board before handing over the $$$

73
Glenn
VK4BG

[DU1GM]

I'm trying to get the PLL board out, removed 5 screws but it seems to be stuck. Is that the rubber pads sticking things up? I don't want to use much force. Any hints would be welcome. 73 de George DU1GM

[VK4BG]

George,

From memory there is a clip on the LHS of the board that holds a TO220 flat pack to the chassis...it needs to be slipped off, and yep...some force can be required to break the board free, especially if the rubber pads have gone" off "....you can place a tool made up of a right angle hook under the board and gently go around , pulling up as you go, till the board breaks free....and double check you have ALL the screws out.

73
Glenn
VK4BG

[DU1GM]

Thanks Glenn. There are two clips on my board and I did take them off, as well as 5 screws. I guess the rubber/glue is still holding the board in place. I put it all back together and the rig worked! I might have removed some contamination by wiggling the board I suppose. Anyway, there was one fault yesterday after a week of bench testing and of course the rig was already back in the rack. It stopped receiving so I switched it off and after an hour or so I tried it again and it worked.

I will make up a tool as you suggest and try to take the board out when the fault re-appears.

There are also other faults in my 706; there is no speaker audio now, either internal or via the spkr socket on the rear. The speaker tests ok though. The rig will also not work with my AH4 auto tuner which works ok on the 756.

Thanks again and 73, de George DU1GM

[VK5APN]

Hi

Had some time today to check out my IC706 MK2.

Removed the PLL board (on the base of the radio and towards the front of the unit), there is 6 screws to remove. 5 for the PCB itself and another screw holding down a TO220 cased device near the front of the radio. Plus the clip on the LHS as previously mentioned.

Could not see any rubber spacer/s. Maybe mine was removed before I purchased it. But then again it is the MK2 not the MK2G. Perhaps they are different in that way as well.

Anyhow here are some pics of the MK2 PLL board removed from the radio.

BTW it helps to remove the coax cables from the top compartment of the radio to gain full access to the PLL section.

Now to reassemble the unit and test.

Regards

Wayne