Another day, another dehydrator

Previously I posted about the Dielectric dehydrator. Here’s another common model, the Andrew / CommScope …. Newer models are controlled by this honking weird motherboard.

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This thing's some engineer's iron clad job security

Basic parts:

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Upper left: black top hat is the air inlet filter that Andrew claims is accessible from the front panel (big fat lie), twist cover and pull off to open. Felt element is easily cleaned. Do not oil, use dry.

Pump: A field rebuildable diaphragm pump.

Center left: vent valve.

Bottom left: Spaghetti Junction.

Center bottom: output pressure regulator.

Bottom right: Coalescing filter bowls. Accessible at front panel.

Right: Molecular sieve unit and air tank.

Top center: Humidity sensor, pressure alarm switch, power input, air output.

Just so you know I didn’t simply open this for fun, here’s what happened on this unit.

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Sliiiiiiimeeeeeee!!!!! The vent valve was blocked and the unit couldn’t drain, so it threw a humidity alarm.

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Water was building up in the coalescing bowls and not being purged. That line at the bottom leads to the vent valve.

How it works: The spaghetti board starts the pump. Air passes left to right through these filter bowls, actually going through them backwards best I can tell. That is to say it enters the inner part of the fiber filters. Believe it or not there is a good reason for this. It then flows through the molecular sieve unit which absorbs moisture, passes through a check valve (where?), and enters the storage tank. From there the regulator allows enough air to pass and pressurize the line. Usually it’s set to like 3 psi.

The tank pressure is gradually increased up to 40 psi at which point the controller stops the pump and opens the vent valve.

When this happens, the pressure in the molecular sieve drops rapidly with outflow to the input side. This causes water droplets to form and be ejected. The water blows back into these two bowls and is vented along with the air via the drain.

Since this is taking place backwards, the bowls are backwards so the droplets will hit the filters on the proper side and fall downwards.

There’s method to the madness, see?

To return the unit to service, I backwashed the vent valve with the air coming from the pump and a snot rocket launched out and went….. Well, it’s never been seen since. Who knows.

It works now, that’s the important part.

And now some hot electronics porn. Here’s a Harris Broadcast ATSC receiver….
Hardcore model.

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Top left: RF and IF board. Right: 8VSB demodulator. Bottom: big mama power supply.

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The 8VSB demodulator.

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Video stream decoder and video output

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Pin count anyone?

This. Unit. Was. Not. Cheap. To. Build. Daaaaaaayuuuummmnnnn

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