icom M421 cutting out

Nos4r2 · 10 September 2007, 16:57

When I transmit on my Icom m421 the screen goes blank, the whole radio cuts out and then a couple of seconds later comes back on (even if I hold transmit down).

I can't find any obvious dodgy connections on the way up to it and the only other thing I can think of that wouldn't need it to be sent back on warranty return would be bad contacts on the mic. Unfortunately I can't figure out how to get the mic off and I can't find the instructions! Any ideas?

jyasaki · 10 September 2007, 17:12

Nos;

It sounds as if you've got an insufficient power condition. Probably due to a poor connection on the 12V supply or return, or, in the case of a new installation, could be too-small diameter wire.

When you transmit, the radio is probably trying to pull in the neighborhood of 5 to 7 amps. Sounds as if you're pulling down the supply voltage enough to kill at least the display, possibly even shut the entire radio off. It comes back on again because once the thing shuts down, it stop drawing power.

You can verify the problem by connecting it directly to the battery with an temporary power feed (use an in-line fuse if you're afraid of the direct connection; won't hurt anything.)

Luck;

jky

Nos4r2 · 10 September 2007, 17:30

That's what I thought but I can't find any evidence to support that after having my head in the console for 2 hours. (granted I need to try powering up with a direct connection).

It'll work with squelch at 0 and volume at full too-and yet won't transmit on low power.

ashbypower · 10 September 2007, 18:01

Nos,
Have you checked the VSWR? some sets (don't know about the 421) will shut down if VSWR is thro' the roof.

Nos4r2 · 10 September 2007, 18:14

No-it was transmitting fine up til about a few weeks ago then it started. It's still receiving OK.It hadn't been used for 3 weeks previously.

I'm not even seeing any change to the display before it cuts out either.

Biggles · 10 September 2007, 18:36

Matt,

Check all the negative wiring carefully. I know its hard because boats always seem to have tons of wiring spaghetti. Might be worth running a new earth !

9D280 · 11 September 2007, 08:29

Nos,

I had exactly that problem about a month ago after I managed to prove SRs also make good paddling pools (don't ask!

) - got salt water into my battery switch, and found a "creeping death" - started as the radio dying when I cranked the engine / transmitted, a week later the engine wouldn't even crank, and even just use of the choke button was enough to kill the VHF momentarily. 2 days later and the battery was as good as a sandbag under the seat for the amount of juice getting through the switch.

One new battery switch later and all worked fine! The moral of this story: check more than just your connections.......

ashbypower · 11 September 2007, 09:58

Quote:

Originally Posted by Nos4r2

No-it was transmitting fine up til about a few weeks ago then it started. It's still receiving OK.It hadn't been used for 3 weeks previously.

I'm not even seeing any change to the display before it cuts out either.

Matt in that case I'm the rest check for a high resistance joint, and switch contacts, before ripping out the TX.

Nos4r2 · 11 September 2007, 18:19

Thats what I'm hoping it is too. I'll have another look through it all before the end of the week and see what I can find.
What seemed unusual though is the cutting out and coming back on while the tx button is held down-ie when it comes back on I've still got the TX button held.

ashbypower · 11 September 2007, 18:26

Matt, have you got a multimeter? if so try taking a voltage measurement at the closest feed point to th VHF and see if the voltage collapses when you TX.

Nos4r2 · 11 September 2007, 18:31

Good idea-cheers! I was going to do a resistance check on the whole lot but forgot the multimeter yesterday and wasn't going to drive 5 miles home to get it(d'oh) so was reduced to looking for obvious bad connections.

Jon Brooks · 11 September 2007, 20:00

I not done already have a look at the in line fuse holders.
Have seen these get very grubby and cause the fault you have.

Cheers

Nos4r2 · 11 September 2007, 21:10

Thanks Jon. I haven't got that far down the loom yet-it's all loomed up and hard to get to. Hopefully thats what the problem is!

Simon B · 12 September 2007, 20:33

Nos,

We're having something similar happen on our boat - spooky!

Nos4r2 · 12 September 2007, 20:53

Wierd. Is it an icom too?

Simon B · 13 September 2007, 15:20

yes a 421 too

jyasaki · 13 September 2007, 15:39

Come to think of it, I fixed a similar problem with some dive buddies' boat a couple of months ago. They had an Icom as well.

Turned out their problem was caused by the wing nuts securing the battery cables. Both pos and neg were something less than finger tight, and though they usually made connection, transmitting would kill the entire accessory electrical system.

Funny I didn't think of that earlier. (or not...)

jky

Nos4r2 · 15 September 2007, 00:24

Sussed it.

A fuse that looked furrier than a furry thing that's just come first in a contest... etc