president HR2510 high swr spikes

[tyler sherwood]

i have a president hr2510 am and fm seem to work ok i get a little over 10 watts on my mfj 941e tuner meter.
but on ssb on a dummy load as soon as i speak into the mic the power goes out but the audio cuts out(on another radio i'm using to monitor it) but when hooked to a antenna on ssb whenever i key the mic the power shoots to about 10 watts and the swr jumps up with it. i'm assuming there might be a short somewhere but not sure where to start.

 

[tyler sherwood]

correction if i speak into the mic on the antenna on ssb i do get audio but only if i speak quietly if i speak a little louder it cuts out and the swr jumps also the audio i do get on ssb doesn't sound great and even on the dummy load there is almost no audio in ssb

 

[Justme]

looks like an RF problem, as soon the RF reaches a certain level the last stage seems to oscillate hence the bad swr and audio going nuts.

 

[sp5it]

Suspected are capacitors between final transistor and antenna socket. When RF voltage goes higher, it might short to ground.
Mike

 

[tyler sherwood]

There are two ceramic caps comeing off the middle leg on either the driver or final would would those be a reason for this one of the legs broke off and a resolderd it but not sure if that could cause this the issues was there before hand

 

[ExitThirteen]

Yes, those caps need to be re-soldered back to the final. Those two caps are there to help with impedance matching on the final. If the caps fell off or became unsoldered, you can experience the SWR spikes that you are currently seeing. The right way to fix it is to install a ceramic or mica insulator between the final and the chassis that it mounts to... when you install that insulator, you won't need the 2 capacitors that are soldered under the final any longer.


~Cheers~

 

[tyler sherwood]

Can you point me to some replacements or the right mica insulator to use been trying find them but cant and do those caps have a certan way they need to go like a electrolytic?

 

[ExitThirteen]

These would be a good insulator to use. These are mica insulators.

https://www.ebay.com/itm/12-BRAND-N...316498&hash=item488bf150a2:g:JOEAAOSwSX9XAxLF


~Cheers~

 

[tyler sherwood]

So when i put the insulator in dont i still need the thermal paste?

 

[ExitThirteen]

Yes, you do. Between the insulator and the chassis, and then between the insulator and the final itself. In short, you'd want to put thermal paste on both sides of the insulator.


~Cheers~

 

[tyler sherwood]

How much do i use and what kind i have some artic silver used for pc cpu and the cooler will that work?

 

[ExitThirteen]

You'll just want to use a little dab on each side of the insulator, and spread it out a little so it covers the majority of the insulator.

Don't use Arctic Silver or any CPU type thermal paste, it can be conductive and you do not want that. You'll want to get thermal paste that is used specifically for electronics, and it will generally be white in color.


~Cheers~

 

[tyler sherwood]

Is there any electrolytic caps that could cause these same issues if the mica insulator dosent work

 

[ExitThirteen]

Doubtful, electrolytics are not going to be the cause of SWR spikes in this case. The 2 disc caps that sit under the final would be the primary culprit here, only other thing that could cause an SWR spike is something at the antenna, whether it's a bad coax connection, or a bad connection within the antenna itself.


~Cheers~

 

[tyler sherwood]

Yeah i beleave its the radio itself ive had 6 other radios plugged intonthe antenna each one worked fine with no swr issues