Magnum S9 low power.

[Ariel]

Hi all,

I bought S9 with dead TX.
With new driver and finals i've got 2 Watts in AM with swing to around 6 Watts.
Bias is ok.
Power growing up when i put wet finger on pins 1 and 2 on 4558d.

Maybe someone know what's going on.

 

[groundwire]

Is that measured in pep or avg on your meter

 

[Ariel]

Old Zetagi SWR power meter mod201.
I think it's AVG.

 

[groundwire]

On a true pep meter its probably alot higher than that

 

[Handy Andy]

There are two versions, both have a "dual final output" amplifier...

MOSFET (claims 50 watts)
and Bipolar...

Go here to locate the radio

MOSFET version uses a trimmer to offset trim ONE final - but EN1230's - both ERF2030 finals


While the Bipolar one simply uses trimmers on bias diodes for the 1969's...


Soo...

Depending on the upgrade, 2 watts seems a little low - at least for any typical wattmeter - both of these pump 8 watts easily at mid-point settings on the AM power.

Hope the link helps!

 

[Ariel]

Board of my S9 is same as 980 version.
Power at watt meter is 0,5 W.

 

[Handy Andy]

Thank you...

Some is helpful but knowing what and how that board is populated, would help because with a Dual Final set up like a linear amp - but the Output TX side running a single part - how the two are interconnected would help.

It usually is simple point to point thru a cap from "Drain" of one section to "Gate" of another but their Biasing might get in the way.


Now for the low power problem - it might be they "destroyed" their rework by removing a jumper they shouldn't have but lost their way or in the case of blown finals a dead short which would make it harder to get the signal to the Power Amp it would show - the Bias would be too low, - which I don't see that - but I cannot determine if the POWER amp side - where all my questions are - is properly hooked up.

If you go over the hookup and jumper and cap interconnection between both stages, you can see where THEIR error was made and all you need to do is rework their interconnection point to point with the right parts in their paths to get both stages.

The Bias voltage looks ok

Nice work so far...keep going!

 

[Ariel]

With burned transistors there was RX ( on s-meter) but there was not anything in speaker.
With new transistor is everything ok.

Red color is fabric connections.

 

[Handy Andy]

I am to guess that the wiring "jumper" connections are working?

I mean, just out of safety as well as to find blown traces, has the coupling caps in between the stages - have they been checked?

I'm not asking for values unless you have a meter appropriate for that, but more like preventing these new finals from getting destroyed from any caps that failed as dead shorts from the excessive problem of blown finals the first time - was there any "welded" dead-short caps?

There are lots of SMD caps on the back side of the board, are they still holding up ok?

Or, are they sucking out the RF the Finals generate before it goes out to the antenna?

You have an RF probe, so run your attenuator (at least 10X down) and scope those same points because the RF side seems to be low to very low - you should be seeing about 40 volts Peak to Peak at C417 or even C460 - those SMD ones located in the Pi filter network, so the Predriver (2) may have to be checked out too.

The Predriver(s) are Bipolar and they squeeze a lot of stuff for bias underneath those RF shields on the foil side.

It would not be a bad idea to rework - reflow some solder in those area to see if it will "wake up"

The Driver uses an EN369 DR suffix. But it appears to be working - just not a lot of signal from further upstream from those Predrivers and Mixer section.