MODULATOR BOARD

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MODULATOR BOARD

Postby K9ACT » Thu Aug 19, 2010 5:56 pm

I am having trouble relating the Rev d schematic with the actual board.

On the input side there is connection called Dgnd between PWin and +V and it is not obvious what to do with this.

I presume it is goes to the Gnd of the PW gen board but it's not clear what to do with the neg side of the power supply.

The board shows a bridge rectifier and transformer inputs but there is no bridge and the ground looks like the same point as the Dgnd.

There are Gnd pads all over the board but none of these are common to the Dgnd pad but should be according to the schematic.

Although the board produces vast amounts of noise when driving the RF deck, it does seem to work properly into a dummy load.

Problem is that it only works when the Dgnd is wired to the one of the GND pads and this does not seem to be the intent of the designer.

Steve seems to be gone again and I am stuck.

Jack
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Re: MODULATOR BOARD

Postby kf1z » Fri Aug 20, 2010 8:16 am

Dgnd is connected to the Gnd pad coming from the pwm generator board, next to PWM out.

In other words, it is the PWM signal GND . Dgnd is labeled "PWM gnd", on the schematic. (output board)

Then the Negative of the power supply for the PWM output board connects to the GND pad next to it.
Not labeled on the schematic, but is the ground point between D514, and D515.


The bridge rectifier is not on any board, usually "dead-bugged" on the top of a transformer that is specific to the output board.

However, some have tapped off the rectifier on the PWM generator board to feed the output board ....
Originally, it was specified that this be a completely independant transformer, or transformer winding, to keep it isolated from any other circuit.
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Re: MODULATOR BOARD

Postby K9ACT » Fri Aug 20, 2010 9:57 am

kf1z wrote:Dgnd is connected to the Gnd pad coming from the pwm generator board, next to PWM out.

In other words, it is the PWM signal GND . Dgnd is labeled "PWM gnd", on the schematic. (output board)



So far so good.

>Then the Negative of the power supply for the PWM output board connects to the GND pad next to it.

Not sure what "it" is. Sound's like something Clinton said.

>Not labeled on the schematic, but is the ground point between D514, and D515.

But those diodes are not on the board. They are part of the bridge we discussed. Question is, where does that ground go to on the board?

Now, after looking closely, I see there is another Dgnd pad next to the 5v regulator. This appears to be common to the other other DGND as would be expected. So am I correct in assuming that this is where the pw sup neg goes?

If that is the case then there is another problem, I think.

I originally tied the neg to the same DGND as the gen board went to which would be electrically the same as using this new found pad.

When connected this way, I could not get any output from the board.

If I tied this ground to the other GND pads on the board, it seemed to work, at least into the dummy load.

Any ideas?

Thanks for the help.

Jack
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Re: MODULATOR BOARD

Postby kf1z » Fri Aug 20, 2010 10:41 am

Sorry "it" meant the "Dgnd" pad.


The ground from the Bridge that is built off the board goes to a ground pad right next to V+ on the output board,
It may also be labeled Dgnd. it is common to the PWM signal ground.


Sound like maybe you have not tied the HV DC power supply ground to the other ground pads on the output board?

Must do that.

That's the only reason I can think you would get no output otherwise.
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Re: MODULATOR BOARD

Postby K9ACT » Fri Aug 20, 2010 1:30 pm

The Gen board ground is connected to one Dgnd and the neg supply to the other.

There is no output to a 5Ohm load with +HV to drains and - to one of the Gnd pads.

I am a bit confused on how the 12v gets to the driver because it is grounded to the floating common and I don't see how it gets back to the 12v power supply.

In fact there is no 12v on the driver and no signal on the gate unless I connect the Dgnd to one of the Gnd pads.

Is there some reason I can not see a gate signal without the HV being on?

js
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Re: MODULATOR BOARD

Postby kf1z » Fri Aug 20, 2010 1:40 pm

oops... double post
Last edited by kf1z on Fri Aug 20, 2010 1:43 pm, edited 1 time in total.
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Re: MODULATOR BOARD

Postby kf1z » Fri Aug 20, 2010 1:40 pm

I'm not sure what you've got going on Jack....
You must be missing another ground or something there.


You can't get a gate signal unless the charge-pump is running.
It will not run unless it has a load.

With the HV turned OFF, you can shorth the PWM output to ground, then you will see a gate signal.
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Re: MODULATOR BOARD

Postby kf1z » Fri Aug 20, 2010 1:42 pm

Is your HV DC NEGATIVE connected to ANYTHING else?

I am sure it is connected to the enclosure.....

But do you have the feed-forward connected, so there is a ground from the HV supply to the PWM generator board?

That may be the bit you're missing.

Not sure
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Re: MODULATOR BOARD

Postby K9ACT » Fri Aug 20, 2010 5:50 pm

kf1z wrote:Is your HV DC NEGATIVE connected to ANYTHING else?

I am sure it is connected to the enclosure.....

But do you have the feed-forward connected, so there is a ground from the HV supply to the PWM generator board?

That may be the bit you're missing.

Not sure


Somewhere on Steve's site it says the feed forward is option so I opted out to keep it simple.

If this is not true, the only other info I have is the note on the Gen schematic that says put a 47k resistor between here and the power supply. It's not obvious what power supply is meant nor which side to tie it to.

js
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Re: MODULATOR BOARD

Postby kf1z » Fri Aug 20, 2010 6:04 pm

The feed forward is an option.... I don't see why anyone wouldn't use it... but if your power supply is really, really, free from ANY ripple, then I guess you don't need it...
If one uses it, the 47k ohm resistor goes to the positive of the HV supply.


Anyhow, the point is, where are your grounds?

Is the HV DC supply negative tied to the PWM generator board?


What you've said is you have to tie the Dgnd pad to one of the other grounds for the PWM generator to work... or rather, to get any output.

So this leads me to think that the grounds, or Negative side of the supplies, aren't tied together, somewhere where they should be.


On my set-up, for the 12v supply for the pwm output board, the negative from the bridge rectifier goes to the Dgnd next to the V+ pad, and the +12v goes to the V+ pad.
The PWM output from the generator board goes to the PWM in pad, and the ground from the PWM generator boar goes to the Dgnd pad on the PWM output board.

Then the HV DC negative lead goes to the GND pads near the output mosfets, and diodes, and directly to the chassis ground at that point as well.

BUT I also have the feed-forward installed.... so the negative of the HV DC supply is tied to the GND pad on the PWM generator board, ( and the 47k resistor etc...)

I mention the feed-forward, because it' the only place I can think of that the HV DC supply ground would be connected to the PWM generator board.
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