HP 547A Current Tracer question

[Borat]

I know of someone selling one of these but they are unsure if it's working and "don't know how to test it". I was wondering how easy they are to repair if it is (as I suspect) faulty? Probably a better way of putting it is: are the parts still readily available?

[timb]

I know of someone selling one of these but they are unsure if it's working and "don't know how to test it". I was wondering how easy they are to repair if it is (as I suspect) faulty? Probably a better way of putting it is: are the parts still readily available?

Ehh, it's pretty simple. All through hole parts. I think it uses a single custom IC, but that could be replaced with discrete parts if absolutely required.

Essentially, as long as the little current sensor isn't broken off the tip of the pen, you should be all right. They're pretty hardy devices, so not much to go wrong.

My unit has been *very* handy several times while debugging stuff. Especially when combined with the Logic Pulser pen! (It can pulse a great deal of current, which can help you find shorts and stuck gates.)

[Borat]

I think it uses a single custom IC, but that could be replaced with discrete parts if absolutely required.

That was really what I was getting at. Do you know what this chip is and if it's available today?

Essentially, as long as the little current sensor isn't broken off the tip of the pen, you should be all right.

Thanks for that!

[HKJ]

You can download the user/service manual from Keysight: http://literature.cdn.keysight.com/litweb/pdf/00547-90006.pdf?id=1850671
It includes schematic.

[timb]

You can download the user/service manual from Keysight: http://literature.cdn.keysight.com/litweb/pdf/00547-90006.pdf?id=1850671
It includes schematic.

That's really bad. Someone here scanned their copy and uploaded it. In fact, just the other night I fixed it up and turned it into a PDF. I'll upload it and link it this afternoon.

[timb]

I think it uses a single custom IC, but that could be replaced with discrete parts if absolutely required.

That was really what I was getting at. Do you know what this chip is and if it's available today?

No, it was a custom HP part. It's basically just an op-amp though. Like I said, it *could* be replaced with a tiny custom board, but I've never seen one go bad before. If anything it'll be one of the power supply or output transistors. Actually, the most common fault would be the "grain of wheat" bulb, which is a 5V 30mA lamp, if memory serves. I've got some, if you need one.

I've actually been meaning to design a tiny little board to replace the bulb with an LED. It's not a straight conversion since the probe puts out 0-5V to the bulb, and an LED won't light under 2.1V. LT makes a neat little voltage to PWM converter in a SOT-23 package, so my plan was to drop that in, so as the voltage from the probe increases, the duty cycle to the LED would increase, thus increasing the brightness in a linear fashion just like the standard lamp.

[TerraHertz]

Here's the schematic in hires. https://www.eevblog.com/forum/reviews/hp-547a-current-tracer/msg533967/#msg533967
Other posts in that thread included the rest of the manual.