X-Force 600HD Smoked

[Shadetree Mechanic]

Hey guys, I need some advice. I have been running my X-Force 600HD with my Stryker 955 for about a year now. The other day I was talking on it on side band and noticed the output power disappeared. I unkeyed real quick and went over to the amp shelf and smelled an electrical smell. I unplugged it and popped the cover off. The smell seemed to be one of the transistors. Also the resistor on the output combiner is toasted. One of the output transformers was still warm, the transformer on the side with the smelly transistor was cold. Like that side wasn't making power.

The SWR when it was in operation was under 1.5 and the Power Max 100 is set at 14.5v. When on AM, the radio was set to a 5w dead key swinging up to about 60w. This gave an output of about 150w dk swinging up to about 600w. This is pep watts on my Autek WM-1. I suspect that the transistors were not well matched to begin with and when the one went out, it took out the balance resistor?

Can I just put in a matched set of transistors and replace the resistor? Or are there other things I should be checking first? Any and all comments welcome.

 

[Shadetree Mechanic]

 

[Shadetree Mechanic]

 

[Shadetree Mechanic]

Here is a schematic that appears to be the standard comp box build and seems to match my box fairly well. The output balance resistor in this plan is 5w and 100 ohms. I think my burnt resistor was 100 ohms but it is hard to tell. Should I use 100 ohms or something else?

 

[2NC995]

Dang, Shade...that always stinks. Just out of curiosity, what kind of power are you putting into it on SSB?

 

[2NC995]

Here is a schematic that appears to be the standard comp box build. The output balance resistor in this plan is 5w and 100 ohms. I think my burnt resistor was 100 ohms but it is hard to tell. Should I use 100 ohms or something else?

Every amp I’ve had in this style has had a 100ohm across the combiner. Yours isn’t a 5 watt (at least it doesn’t look so from here)...but probably a 2 watt.

 

[Shadetree Mechanic]

Dang, Shade...that always stinks. Just out of curiosity, what kind of power are you putting into it on SSB?

And it had to be when my vacation started too. The Stryker 955 puts out about 60w peak on side band.

 

[Shadetree Mechanic]

Every amp I’ve had in this style has had a 100ohm across the combiner. Yours isn’t a 5 watt (at least it doesn’t look so from here)...but probably a 2 watt.

Yes I think mine was a 2 watt. The plans show a 5w but I am thinking that as long as the transistors are matched, this resistor should not get hot?

 

[2NC995]

Yeah, timing never works out does it?

I am asking more for the sake of taking a guess at what to expect with the straight 4 I’m working on...but for the sake of discussion, my DX500 stops producing power at a much lower level. I don’t fully wrap my head around the differences.

I’m with you on the resistors. I’ve always been under the impression that the 5 watt is a bandaid for mismatches. And actually, the powerplate I have, built from the plans you posted, has the biggest resistor I’ve ever seen used.

 

[2NC995]

Did any of the 10 ohms smoke? I can’t see the one on top per the pic?

Actually....it looks almost as if it blew completely out.

 

[Shadetree Mechanic]

Did any of the 10 ohms smoke? I can’t see the one on top per the pic?

Actually....it looks almost as if it blew completely out.

Ten ohms? The only thing that looks burnt is the output balance resistor.

 

[Shadetree Mechanic]

Here is another shot. The sand bars on the input are huge.

 

[2NC995]

The photo shows the one on bottom transistor in your photo...left bank of viewing from the input end. Each transistor will have one to ground. A transistor blown will usually smoke them...hence the saying, “try not to choke on that 10ohm smoke”.

I can’t see the one on the top transistor well - but it looks like it could be blown apart?

 

[Shadetree Mechanic]

It appears to have some kind of bias network.

 

[2NC995]

I sent while you were sending the additional photo...it looks like it’s just hiding behind the disk capacitor now that I see it from a different angle. Anyway, if any of those 4 little 10ohms is blown, you’ll know which transistor is smoked.

Not that it will matter if you put all four in, but may narrow your troubleshooting if you salvage the parts.