Optima MK3 took a dump

[camaro1]

Dang,, my favorite of all the export radios went out on me the other evening, had this one for about 3 yrs from yeticom, always my go to radio for talking with the locals, went to key it up and noticed there was no meter movement on the radio,, then the radio shut off. fuse blew. this radio has always had the variable power turned all the way down and would run 8-10 WATTS pep running into another small box. finally got around to pulling the covers off and did some basic checks, the finals were showing a short to ground so I pulled the jumper that is back by the finals then my dead short was gone, I powered it up and it receives fine, so one of the 13n10 mosfets went out,, no reason why, I figured it would last many more years running that low of power out of it.

looks like quite a job to get new mosfets in it, double sided smt board and no room,, it looks like the leads bend up through the bottom of the board and are soldered on both sides,, plus I don't know if they took any other parts out when they shorted out

 

[tba02]

Sad news.

 

[222DBFL]

Sad to hear!! Mine is still going strong. I remember asking you about the after speaking to you on yours! Made my mind up real fast! Hope you get it fixed!! Great radios. Wish they still made them.

 

[Blackcat630]

Bummer

 

[Mudduckmobile]

Dang,, my favorite of all the export radios went out on me the other evening, had this one for about 3 yrs from yeticom, always my go to radio for talking with the locals, went to key it up and noticed there was no meter movement on the radio,, then the radio shut off. fuse blew. this radio has always had the variable power turned all the way down and would run 8-10 WATTS pep running into another small box. finally got around to pulling the covers off and did some basic checks, the finals were showing a short to ground so I pulled the jumper that is back by the finals then my dead short was gone, I powered it up and it receives fine, so one of the 13n10 mosfets went out,, no reason why, I figured it would last many more years running that low of power out of it.

looks like quite a job to get new mosfets in it, double sided smt board and no room,, it looks like the leads bend up through the bottom of the board and are soldered on both sides,, plus I don't know if they took any other parts out when they shorted out

Yeticom is on the set sometimes, send it in get it fixed....It sucks, but if you love, and cant do it some one can, theres alot of good folks on here that like the optima mk3, I'm one but I sold it to get something I think is better....But I do love that nice little rig, It's a talker with a 102 at the other end. Sorry for your loss.

 

[Onelasttime]

The non-rf Mosfets seem to be a constant failure point in every radio that uses them. Has anyone tried replacing them with bipolars. I do not care about a power loss since rf power is far more important that pep and bipolars tend to make far more rf power at the same voltage and swing less widely.

 

[Onelasttime]

I just ordered a matched pair of 2SC1969's and matched pair of 2SC2166's......I am considering ordering some 105 or 125 degree caps that are at least 3000-5000 hours and see if these two thigns does not solve all issues with modern black box radio's! I hear that Anytone radio's will sometimes die suddenly and it is again either the fet's or the lytics that go on them.

 

[Robb]

Only time I see mosfets going bad is when they are just pushed too hard. Cheap fix, since you get them for around a buck apiece.

 

[Onelasttime]

I have no doubt they being pushed too hard. I see all kinds of RCI2970N2's locally with the 13N10 cracked in the amplifier section. It is seldom more than one but it only takes one to take the whole thing down! On the other units that use them again you either see a short or physical cracking. Which came first the short or the physical cracking?

Yes you can get an entire sleeve for less than $20. If I was doing repairs for a living I would be a happy camper but this is personal I want this radio to duplicate the 12+ years of perfect service I have traditionally gotten in a mobile environment.

I am not convinced that the real world performance of these radio's is replicated as compared to how they perform on a meter. In fact I have been fairly disappointed by the distance and on air performance achieved by some of these radio's that show very impressive pep number's on a meter.

In some ways they remind me of high horse power engines with no torque that only make power at really high rpm's. They look good on paper and can be made to work on the race track but seldom pan out in the real world in daily driving.

Because these fet's are no RF specific transistors and not even really rated for the voltages we use them at you have no real gain figures for them. Most fet's do not make very good gain at lower voltages and most have terrible tolerance for swr mismatch!

 

[Robb]

Like I said - push them too hard and they snap. Even with a heat sink, it is no guarantee because the mosfet's internal junction temperature can rise much fast than it can be effectively cooled by the heat sink. Pop goes the mosfet . . .

Remedy? Run the radio 5-6w less rated peak output and keep an eye on the modulation level. Too much modulation will serve to overdrive it/overheat the junction too.

I have several radios that have been subbed out with mosfets, since it is a cheap/fast fix. Never had a failure yet. Always, and I do mean always - gets good reports. But I use a top grade antenna and have zero problems getting out. Don't like mosfets in a mobile situation, unless the antenna is kept properly tuned and maintained.

 

[camaro1]

don't know the sudden interest in this thread ,,, but the radio in the first post was always ran with the variable power all the way down, putting out 8-10w pep , so not really sure what happened

 

[Robb]

. . . Mosfets are a bit more sensitive to poor/bad antenna match.

One more thing. Never accept the OEM integrity of the heat sink. I take them off and make sure they are completely flat on the mating surface by sanding them with wet or dry #400 sandapaper using water on a flat surface. Then I make sure that its mating surface is free of burrs of any kind. Then I add some compound Z9 heat sink paste.

Attach the heat sink to the finals/driver screws first; then tighten up the rest of the screws. Wipe off excess compound from the edges.

You can also use a mica insulator on the finals/driver with new paste instead of the OEM thick white insulators. Better to be a bit generous with the paste and wipe off excess, than to have a dry spot anywhere on both sides of the insulator. Always clean off the original paste before applying fresh compound.

 

[543_Dallas]

The non-rf Mosfets seem to be a constant failure point in every radio that uses them. Has anyone tried replacing them with bipolars. I do not care about a power loss since rf power is far more important that pep and bipolars tend to make far more rf power at the same voltage and swing less widely.

Could you explain the difference between rf power and peak envelope power for those of us that don't understand?

 

[bob85]

"Could you explain the difference between rf power and peak envelope power for those of us that don't understand?"

Not in a way that would make sense