Talked to Chip @ Radio Shop Supply today. He said he hasn't heard of this issue yet. Said amp stage has been the same design for long time.
He also mentioned that the issue should have shown up on a dummy load. He also stated that during their checks, they put the radio under a 2.0:1 load.
I told him that all of my other radio's (and I have a rather large assortment) and my two solid state amps all act normal on my Gainmaster and my dipole. Even my recent Palomar 450 FET showed a flat SWR on the output end. However, it had a crappy input match.
What else could possibly cause the high SWR on transmission into a nicely resonant antenna system?
I could speculate all day long. It's also strange that a local (whom I don't know) was reporting a finicky SWR with his recently purchased N2.
Could be a production run hiccup.
I haven't been in the service field for almost 15 years but I have to tell you Chip is not likely to fix this problem just by this one statement "He also mentioned that the issue should have shown up on a dummy load. He also stated that during their checks, they put the radio under a 2.0:1 load." Nothing says he doesn't understand the problem clearer than that. Perhaps you can teach him after reading this.
He first has to understand that the problem is not SWR related. The SWR is the result of the problem and not the cause of it. The problem is the transmitted signal contains the desired frequency AND spurious emissions that are far enough away from the desired frequency that a typical antenna cannot match the spurious frequencies with a good SWR.
If we test this radio into a dummy load even at 25 or 100 ohms (2:1 SWR), the problem will still be perfectly hidden from the tech because the resistive dummy load is the same impedance to both the desired frequency and the spurious frequencies. Even if Chip does not test with a spectrum analyzer or antenna, he can still spot this problem by using a antenna tuner into the dummy load.
Once you tune the antenna tuner for a good SWR into the dummy load, you have turned this wide band resistive load into a narrow band, resonant load. Now if you make a big change in frequency, the SWR will also increase noticeably. Chip will not be able to set the antenna tuner to provide a good SWR with the dummy load no matter how he tunes it because the tuner will not allow him to perfectly match two frequencies this far apart.
If he is able to "repair" the radio, another forum member has already pointed out the next test to see if it is truly stable. If the antenna tuner can provide a perfect SWR, now SLOWLY adjust the tuner for a 2:1 SWR. If at anytime you see a sharp spike in SWR or power rather than a slow increase, the amp section is still unstable.
One is going to have to think outside the box to fix this problem because you cannot go at it thinking you're going to find a bad component. This is not a bad part, it's a bad design. That could be anything from the physical layout on the board allowing RF feedback to the cheap MOSFET finals in the high power amp.
The very first thing I would consider is that this amp is attached to a radio. That alone present its own share of RF feedback problems associated with decoupling the amp from the DC power wire that also feeds the radio. Rule out the simple possibility that the "engineers" overlooked this by powering the amp section from it's own isolated power supply.
I haven't seen the inside of this particular radio but I think it has he heatsink in the bottom of the radio where the speaker would be. Someone check and see if they have a metal shield over the top of this amp section. If this has been left out and they have the high power amp right on top of the PLL section, I'd expect it to never work like that.
