Entry level Equipment Recommendations!

[larrymoencurly]

Re: Entry level Equipment Recommendations!

The $3 Harbor Freight multimeter is surprisingly accurate, at least for DC and ohms (the only things I can verify), but one of the tips pulled out when I tried to measure an AC outlet (applied lacquer thinner and pushed the tip back in, hasn't come loose since).

[Jack Crow]

Re: Entry level Equipment Recommendations!

Hi Jack, can i have the drawing of your homemade curve tracer, and a picture of it?

Thanks

Hi again,
When in Kuwait I ran the electronics section of a military generator repair shop.

One of the things I did there is write a Power Point book on how to fix the units. It's huge over 150mega bits.

As part of the book I had notes on special tools, such as the XY tester.

I have a 'short' edition of the book that can be e mailed and it's in there.
So if your system can take an 11mb file I can send it to you.

Shoot me an e mail at...

ka2zev@yahoo.com

In the mean time I will try to re draw it.

The article also shows some sample displays of working and failed parts.

As for a photo of the one at home.
It's ugly. I have looked at better foot fungus.
A classic ham radio project held closed with tape.
Not a proud moment.
Yet it works.
Made from an old wall wart power supply.
If I take a photo of it I will be open to blackmail.

That's the story at this point in time. Sunday evening. 02-20-2011.

Keep it safe
Mike in VA

[Jack Crow]

Re: Entry level Equipment Recommendations!

Guys,
Found the sketch from my book.
Due to the creeky way this computer works I had to print it, then scan it as a JPG, and post that 'photo' on my Flickr photo site.

I have used one of these units for years. Got turned on to it by some very good repair guys that worked for PRD Electronics in Syosset New York.
Some time in the mid 80's.

Tools like this have been around for years in different styles.
A web search will bring up a bunch of different internal arrangements.

Like many instruments you will get one set of readings 'in circuit' and another with parts isolated.

I use the tool to pick out parts for later examination out of circuit. I used go go through a CB set in about 10 min. Diodes, transistors, some caps and coils. With it I can pick up the easy problems fast. Some for most switch mode p/s units. Amplifiers big and small. If you work on power analog electronics, this thing is great.

Here is a link.
http://www.flickr.com/photos/90108848@N00/5467708249/

Couple of things.

You need to think.
It's not as easy as it looks.
This tool requires a little brain work to make a success of the recovered information.

To make this work you need a dual channel scope set up as an XY display.

Like the instructions on the sketch say, set up the coax cables so that the display shows the standard things.

Open an H line.
Shorted a V line.
Diode across the probes, should display an "L" shape.

Test a transistor by probing B to E then B to C.
You should get two good angles showing the NPN or PNP junctions.
The red/black wires called out for on the sketch is just a name.
Since the test signal is AC, it hardly matters.

For discussion...

Let's pretend your checking out a home stereo receiver with a failed channel.

You can't use this in a system that is turned on or plugged in.

Unplug and disconnect the Unit Under Test (UUT) from everything.
Ground isolate the UUT!

The tester makes about 6 volts or so of AC at a fairly low source Z.
Some parts may not survive this much current.
Low value Pico fuses come to mind. It will light an LED if that's any help.

Semiconductors that are tested 'in circuit' will have all kinds of stray stuff on them.

The key thing to look at is the right angle junction.
In circuit readings will take some thinking to either approve or reject.
So use it often.

Things that indicate a bad semi.
A blown open joint. No conduction or a line indicating a resistance.
A curve rather than a sharp angle.
That indicates a leakey junction.

If the part is removed from the circuit and the display shows an angle other than 90 degrees, that's a warning.

Power FET's are a special case.
Put the probes S and D, then touch the G with a finger tip.
You will see how stray noise in the room will turn the fet on and off, and a twitch in the display.

Caps and coils will show a distorted circle. With a 60hz test signal your kinda limited to what the parts will react to.

Hope this helps.

Jack Crow aka Radio Mike
Herndon VA

[Jack Crow]

Re: Entry level Equipment Recommendations!

Hi all,
I go through the work of posting a print and it seems that nobody has gone and looked at it.

What gives.
Mike in VA

[Cosmicape]

Re: Entry level Equipment Recommendations!

Guys,
Found the sketch from my book.
Due to the creeky way this computer works I had to print it, then scan it as a JPG, and post that 'photo' on my Flickr photo site.

I have used one of these units for years. Got turned on to it by some very good repair guys that worked for PRD Electronics in Syosset New York.
Some time in the mid 80's.

Tools like this have been around for years in different styles.
A web search will bring up a bunch of different internal arrangements.

Like many instruments you will get one set of readings 'in circuit' and another with parts isolated.

I use the tool to pick out parts for later examination out of circuit. I used go go through a CB set in about 10 min. Diodes, transistors, some caps and coils. With it I can pick up the easy problems fast. Some for most switch mode p/s units. Amplifiers big and small. If you work on power analog electronics, this thing is great.

Here is a link.
http://www.flickr.com/photos/90108848@N00/5467708249/

Couple of things.

You need to think.
It's not as easy as it looks.
This tool requires a little brain work to make a success of the recovered information.

To make this work you need a dual channel scope set up as an XY display.

Like the instructions on the sketch say, set up the coax cables so that the display shows the standard things.

Open an H line.
Shorted a V line.
Diode across the probes, should display an "L" shape.

Test a transistor by probing B to E then B to C.
You should get two good angles showing the NPN or PNP junctions.
The red/black wires called out for on the sketch is just a name.
Since the test signal is AC, it hardly matters.

For discussion...

Let's pretend your checking out a home stereo receiver with a failed channel.

You can't use this in a system that is turned on or plugged in.

Unplug and disconnect the Unit Under Test (UUT) from everything.
Ground isolate the UUT!

The tester makes about 6 volts or so of AC at a fairly low source Z.
Some parts may not survive this much current.
Low value Pico fuses come to mind. It will light an LED if that's any help.

Semiconductors that are tested 'in circuit' will have all kinds of stray stuff on them.

The key thing to look at is the right angle junction.
In circuit readings will take some thinking to either approve or reject.
So use it often.

Things that indicate a bad semi.
A blown open joint. No conduction or a line indicating a resistance.
A curve rather than a sharp angle.
That indicates a leakey junction.

If the part is removed from the circuit and the display shows an angle other than 90 degrees, that's a warning.

Power FET's are a special case.
Put the probes S and D, then touch the G with a finger tip.
You will see how stray noise in the room will turn the fet on and off, and a twitch in the display.

Caps and coils will show a distorted circle. With a 60hz test signal your kinda limited to what the parts will react to.

Hope this helps.

Jack Crow aka Radio Mike
Herndon VA

This is awesome, thank you very much