Percussive Maintenance

I was testing something with my trusty old Tektronix 2232 100 MHz digital storage scope and this happened:

image

My guess as to what I’m seeing: a pretty significant bit of the input to the DAC (digital to analog converter) that sets the beam’s horizontal position is stuck, causing the display to break up and overwrite itself in unreadable stripes.

This display is of the vector type. There is no linear, raster scanning like in television or computer monitors; it’s more like an electron beam Etch-A-Sketch. Two DACs driven by the microprocessor set the beam’s horizontal and vertical deflection and it excites the phosphor wherever it lands. A control grid in the cathode ray tube allows it to be blanked to be moved without lighting the phosphor it crosses.

When this skipped around the beam wasn’t blanking; you could see it smear right back.

I tried power cycling. It’d be okay a minute or so after a minute off then do that again.

I tried clearing all settings and memory.

I tried looking through the service manual.

Then, finally….

I smacked it.

Gong!

The problem immediately cleared and does not come back.

Why didn’t I try this first? Am I losing my mind here?!

The fault was likely a loose connection at a backplane connector, socketed IC, or ribbon cable down inside, or maybe even a cracked solder joint.

If it recurs I’ll investigate, but for now I’ll rest easy knowing I don’t have to replace this wonderful scope I’ve used for years with some soulless modern piece of Chinese plastic poo that can’t actually do X/Y plot mode right.

Weston Super Sensitive Analyzer

For a while I’ve wanted one of those Simpson multimeters like we have at work, with the big needle analog meter…

Today I found something a little neater. Someone set one of those Harbor Crack multimeters down on top of it and I laughed and groaned at them all at once.

image

image

image
Needs work in the battery area
image
Great! Where's my nearest radio parts distributor or jobber?

image

image

image

image

image

image

The gunk on the faceplate cleans off easily. Now I just need to make up new test leads and it’ll be good to go.

The meter has a hilarious ballistic to it. It’s not entirely undamped, but it basically overshoots the reading once then drifts back down onto it. I’m guessing that’s the result of the armature coil being a bit heavier than usual from all the turns to make it… super sensitive.

On a side note I’m looking at the schematic and there’s no diode to rectify AC to DC for the meter… This means the meter must actually have a field winding for AC measurement and thus, by design, it’s true RMS! Not bad at all for a meter made in 1948.

Just thought you should know…

I have a thing for hand drawn traces.

image

image

This is on a Shure M267 mixer. I’ve seen at least three different variations on this same mixer. The one I’ve got at home contains only one transformer, at the output. This one contains five.

image

image
Who wired this nutty thing? Me?

image

“Vactrol” style lighted photocell in optical limiter circuit. The audio envelope is detected, amplified, passed through a slow filter and applied as a bias voltage to adjust the light brightness. The photocell half of the device is used as a variable attenuator to back the volume down as needed to prevent clipping.

These devices are also commonly used in DJ mixers.

Transmitting from the Troll Bowl

You know you’re doomed to be an RF person forever when you look at this…

image

… And just keep thinking “damn that’s cute”.

That’s a Troll auto tracking antenna system for broadcast microwave from a helicopter.

image

image

Swapped this corroded yackage out. So far, so good.

image
Hey News Desk, can you hear me now? Good.

image

image
Whose AM DA is this again? North of US 41, just west of 137 Ave...

image

I could never do this stuff regularly and am really hoping this project’s done. For a good long time. The Jet A fumes make me feel sick after a while of working around the bird or after being in the air a while. It’s not motion sickness; I literally just don’t get that… it’s the fumes. Yeeech. The weird part is when turbulence rocks the craft, it makes me feel better for a bit??

Can’t explain that one. Dammit I’m a broadcast engineer, not a doctor.

image
Good day, sir.

The whirlybird

We’ve had an ongoing issue at work with the helicopter’s MRC microwave transmitter powering down on us. The silly thing is really obtuse; the user interfaces won’t tell us after the fact why it happened. Don’t you love faults like that? It’s almost as great as on ham and other 2 way radio equipment where a high VSWR condition causes the transmitter to fold back its power output but not indicate to the user that this is happening. Come on man…

Anyway here’s the box.

image

image

The remote controller at bottom. The top unit is the N Systems antenna pod controller which allows aiming of the antenna or selection of which receive site to automatically aim at. The NSI antenna’s servos make a comically mad sound as the unit initializes on power up and they seek home position at full tilt.

image

The bird at roost.

The fault cannot be replicated on the ground; this has been tried several times with no success. Therefore the only way to figure this out…..

image

That’s Hollywood Beach down there.

image

image

I believe this is where parts of “Santa and the Ice Cream Bunny” were filmed, notably the fire truck driving through the dirt road and Tom Sawyer and Huckleberry Finn rafting down a waterway accompanied by “Old Man River” on kazoos.

I Am Not Making This Up. This film is fascinating as hell.

image

The A/V box. At right, radios and audio controls. At left, video switches, CCUs for a couple of small Toshiba cameras mounted in the helicopter interior.

Never photographed because I simply forgot: the FLIR pod ‘laptop’ controller. It’s a big chunky panel you actually just rest on your lap while using it, with a damn near fire hose sized cable coming out.

image

At about Atlantic Shores Boulevard.

image

Suspicious: this isn’t the RF cable for the MRC radio but was installed at the same time and is identical. To be replaced MoNday.

Part of the testing included putting a phone in there recording video of the transmitter front panel. What it revealed was just the unit going into standby and back. No informative messages. Meeehh!! I don’t know if these MRCs keep an internal log file like Nucomm radios do.

image

It Fell Out Of The Box Like That!

Really.

Seriously.

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

Aaaaaaaaa
AAAAAAAAAAAWHATTHEAAAAAAAA

What.

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.

The external converter.

Excuse me, I’m going to go wash my hands.

How do you even let this get past QC?

Ordered a replacement screen and frame for my broken Galaxy S4.

What came just… failed

image

Original frame at right,  motherboard next to it.  Note the puzzle piece shape that accommodates those SMT parts.

image

Old at right,  new at left.  Note no indent for those smt parts.

image

Foiled by Chinashit. Can’t blame me for trying can you?

How to use your racks and avoid unspeakable engineering horror

On most equipment racks you will find the following pattern of holes:

** * ** * ** * ** * **

No, it was not drilled by a drunken woodpecker.

image
But this gear was installed by a drunken bonobo at 4 am.

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.

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.

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

Basic parts:

image

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.

image

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

image

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.

image

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

image

The 8VSB demodulator.

image

Video stream decoder and video output

image

Pin count anyone?

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

Happy Monday morning, everyone!

image
Pissbomb

Marshall Electronics makes some nice rack mounted monitors that are paired to

the

freaking

worst

power supplies ever.

You haven’t lived till you’ve had a power supply urinate in your hand as you unplug it.

image
WeeWeeCon, made in the People's Republic of Screwthis

The good thing is, it’s just +12VDC. Easy to find a better power supply and attach the power cord to it. In some cases you can also get in there and recap these but this one’s done, it got pissbombed.

1 2 3 4 5 11