New Hobby

I recently mentioned in a post that I might be picking up a new hobby that should have good synergy with my woodworking hobby.

That new hobby would be repairing electronics - some of which might even be old enough to be installed in damaged wooden cabinets.

Background:  The first school that I went through in the Navy (after boot camp) was Basic Electricity and Electronics (BE&E school).  It was different from all the other schools I attended up to that point, because it was self-paced, and it was computer based.

It was fascinating learning about simple circuits, and the relationship between current, voltage, and resistance.  Students learned about capacitance and inductance, how transformers and rectifiers worked.  How transistors worked in a few simple circuits.  The final pass/fail exam was in an electronics lab where you troubleshot a simple AM radio to figure out why it wasn't working.

To pass the final exam, students used a signal generator to inject a radio signal into different sections of the radio.  Then students would use an oscilloscope to determine where the injected signal was good, and roughly where it stopped passing through the radio.

I'm pretty sure this was the oscilloscope the school used to teach the class - The Tektronix Model 2235, also known by its military number, AN/USM-488.

I remember at the time thinking how beautiful it was, with that cool blue screen with the time and voltage graduations.  At the time it was the most complex and fascinating instrument I'd ever used.  That was before I got to play with submarines, generators, gas turbines and nuclear reactors.  I'm still quite fond of oscilloscopes though!
 
After getting a rough idea where the signal failed to get through the radio, students would have to use a multimeter to identify the specific component that had failed.  Excellent training!

For the record, I failed the final and got my butt chewed out pretty good.  I was freaking out about the second attempt, but managed to pass it.  After that, I was sent to Illinois for Electrician's Mate school, and then to Florida for Nuclear Power School.  I never used the cool knowledge or skills from BE&E school again... until now.

So I'm thinking that it would be fun and maybe even profitable to restore vintage or antique electronics.  To that end, I recently bought from an online auction, a 0-60 Volt Linear DC power supply.  It cost $10 to purchase, but the shipping was another $30.  Holy cow!  Linear power supplies require a massive transformer, which adds a great deal of weight to the device.

The note on the online auction said "not tested".  From now on, my working assumption of that statement will be: "Doesn't work, and is probably not repairable". :)

This power supply will be a very useful piece of test equipment - if I can get it to work.  It's pretty vintage itself.  If I can get it working, that will give me a bit of confidence to go forward.  Might as well show some pictures of it.  Click on any image to enlarge.

Cosmetically, it arrived in fair condition.  There was some red spray on the face.  I got a little too aggressive and used brake cleaner.  That softened the plastic on the meters, and they developed a nasty haze.  I had to buff them quite a bit to get rid of the haze.  On the painted areas, I got rid of most of the rest of the paint with a Dremel tool equipped with a pointed buffing tip.

The fuse cap on the right is missing, and so is the 1-1/4" fuse.  I'm assuming that since it is near the output jacks, it is an output fuse.  I took a chance and powered the unit up.  The voltage meter deflects only a little when the main power is switched on and the voltage knob is cranked up to max.  So we have an issue.

Below, cleaned up.  Cool neon glow-bulbs!

 It was pretty grimy inside.  Also all the screws that hold the top and bottom on are missing.

It cleaned up well.  What components have we got here?  The gray object at the right is the heavy input transformer that made this so expensive to ship.  It drops 120 Volt line voltage down to about 80 Volts AC.  Power then goes to the top right section with the little fan, where it is converted to DC at about 80 Volts.  Next it goes into the big orange capacitor which smooths the remaining ripple out of the DC.  Such capacitors are called filter capacitors

Below is what the rectified DC voltage looks like with and without a filter capacitor.  Diagram courtesy By SpinningSpark real life identity: SHA-1 commitment via Wikipedia.  Filter capacitors simply accumulate a charge while the voltage is high and discharge when the voltage falls off, helping to maintain voltage. 

Below, the rectifier section with a cooling fan, before cleaning.  This seems to be working OK.  It has been cleaned since, and looks pretty nice now.  This is as-found.

The left side of the cabinet contains a circuit board that I believe are the controls for adjusting the DC output voltage.  I've probed the major components with a volt meter, and they work.  What doesn't happen is we don't see an output voltage.  Below, that circuit board as it arrived.

Below, cleaned up.  This appears to have had some work done, and I'm leaning toward this section being the issue - or at least part of the issue!  We shall see.

***UPDATE***

OK so I've poked around in this power supply inspecting it visually, and checking things with a meter.  It's pretty clear that someone has been here before me.  I'm not all that knowledgeable about this sort of stuff, but I found an obvious issue just coming from the 120 Volt input line.  The hot and neutral leads were installed backwards.

Resolving this doesn't solve the problem of lack of an output, but it does show that whoever removed and re-installed the power cord (and whatever else was done) wasn't particularly competent.

First off, the cord goes through the back of the panel without a grommet to keep it from getting cut.

 

This is after I pulled the cord out of the hole and soldered the white and black wires to the correct terminals. It's a temporary connection, so I'm not too worried about the solder joints for now.

Some of the tools needed.  A soldering gun is a good choice for big terminal lugs like the ones above.  It takes a lot of heat to get those bigger chunks of metal warm enough to melt solder.

 Here's how it was initially wired.  I'm not the sharpest tool in the shed, but even I know that the hot is supposed to go straight to a fuse.

 I've been looking online for a manual for this thing.  The only manual I found so far was for a different model by the same company - for $25.  More than I paid for the power supply!  I think I will spend more time researching and trying to figure it out on my own...