A refurb DirecTV Slimline receiver we had in service a while just up and died with no warning. It was opened up and showed no signs of trauma but I saw something everyone else missed….
Hmm. Let’s flip it and see what that is at the edge. It’s probably nothing at aaaaaaaaaaaaaa
A while back I found these units tended to burn the access card. This appears to be the fix – first, note how far heat would have to travel down those fingers to toast the card. Second, the card is actually heatsinked by a plate above the socket.
Front panel with mystery antenna. Also note the dual die IR LED next to the black lens IR receiver. This is probably used for the unit’s very user – friendly universal remote system.
The rectangles are touch button sensors.
RF filter and very big silkscreen note on where to find power.
On most equipment racks you will find the following pattern of holes:
** * ** * ** * ** * **
No, it was not drilled by a drunken woodpecker.
See the holes with the wider spaces between them? Good… IGNORE THEM! They do not exist! You never saw them. Fnord.
See the closely spaced holes? Imagine they’re the dots on a double 1 domino. This means there’s a center line between them. See attached photograph. The center line will be the edge of each piece of equipment to be mounted.
Why are the center holes there? Okay… Fine, I’ll admit to their existence. Begrudgingly…
Some oddball accessories like cover blanks and cable lacing bars may be screwed in here. In the case of cover blanks it’s usually on weird ones that have a single hole in each end of a 1U* high blank. If you install a lacing bar this way it will be in the middle of one rack unit space – handy for the rear rails behind a patch panel.
Otherwise, do not use them unless you really have good reason to.
If you do mess this up…. Well, look at the wonderful mess in the photograph. Huuurrrrrgghhhhhhhhhbbllll.
Previously I posted about the Dielectric dehydrator. Here’s another common model, the Andrew / CommScope …. Newer models are controlled by this honking weird motherboard.
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.
Sliiiiiiimeeeeeee!!!!! The vent valve was blocked and the unit couldn’t drain, so it threw a humidity alarm.
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….
Top left: RF and IF board. Right: 8VSB demodulator. Bottom: big mama power supply.
The 8VSB demodulator.
Video stream decoder and video output
Pin count anyone?
This. Unit. Was. Not. Cheap. To. Build. Daaaaaaayuuuummmnnnn
Here’s a look at a very curious mystery on a Brother MFC-J435W. On this printer the ink cartridges are loaded at the front panel and a set of small (silicone?) hoses carry the ink to the print heads.
This is what they’re supposed to look like. The printer was brought to my desk after a new set of cartridges were loaded and it only printed black. I didn’t get a photo of it but the ink lines were totally empty…??!!
So how do you prime the lines? Well, Brother thought of that. The rubber cap that seals the printhead when not in use is connected to a vacuum pump.
The cap and squeegee blade used to wipe the head are visible at the end.
Triggering the clean cycle over and over finally primed the lines and the color output slowly returned.
So I’ll answer this mystery: What does an inkjet cleaning cycle do? Well, first off, the printhead periodically moves to an ink toilet off to the side and wastes some ink to keep the ink in the passages fresh. This is audible as a soft high pitched (about 5000 Hz usually) tone.
Second, a squeegee is moved into the printhead’s path and it’s wiped clean of any dried or accumulated ink. This is typically done during print jobs as well and can be heard as one or more clicks.
Third, during manually initiated cleaning or priming cycles or after installing new cartridges or printheads, the printer uses the big suck to prime the ink feed system.
This vacuum pump isn’t present in all printers. Generally if your printer uses cartridges where the printhead’s changed along with the cartridge, it isn’t present or needed, and if your printer has permanent heads (Epson) or uses tubes like this one, a priming pump is used.
Long ago NeXT made inkjet printers that even had vacuum switches so it could confirm when the ink was primed and fix it if not. Most ain’t that fancy.
So if your printer drops a color, look for these clear tubes – they shouldn’t be!! If the vacuum pump isn’t doing its job, make the printer move its head then cut the power while it’s uncapped. Clean the cap/vacuum with a wet paper towel or cotton swabs. The ink will stain fabric and skin. You were warned. Power back up and see if it’s happier.
Only major gotcha here– repriming the color ink lines consumed a full cartridge!