Unit will no longer power ON

> specific 22 uF capacitor

Just a small can electrolytic, anything between 10uF and 100uF, voltage 25V and 50V.   In the photo it's the one with the arrow (in my unit it actually was 2.2uF, way too small!)

Here's a stupic question... I can totally remove and replace the capacitor.

But I've never seen the 45 degree wire connections to the PCB before. How do I release the wires from the PCB connectors, so that I can take just the PCB to my lab?

Okay, I fifured out how to remove the wires, and then the top PCB plus bottom PCB plate.

Remove the bottom PCB plate plus potted assembly looks daunting, having to unsolder all those leads.

Has anyone run things out to see whether I could simply add a capacitor to top-side only accesible pads< so that removal of the bottom PCB would be unneccessary?

> Remove the bottom PCB plate plus potted assembly looks daunting, having to unsolder all those leads.

Don't remove potted assy unless the power-FETs were blown.  To get to the board bottom, just unscrew aluminum slab from bottom plate.

> see whether I could simply add a capacitor to top-side

This "supply boot" capacitor connects to the UC2844 chip, neg to pins 8,9, and pos to pin 12 Vcc.  Since we want to increase the value, just add a new cap in parallel.

So, either fine soldering to SMT chip, or try chopping the capacitor in half with cutters, remove detrius and the rubber plug, which leaves two leads sticking up.  (First mark the + - polarity before destroying capacitor!)

The T.I. spec sheet for UC2844 gives 120uF, 35V for the capacitor.  Anything above 22uF should work. 

We have a model 5415D that is doing this.  We are getting power past the switch.  I'm glad I found this thread!

I found this capacitor at Newark's website for 34 cents...

Any "radial" electrolytic capacitor works, 25V or higher, with value between 10uF and 100uF.

JJabolonski and Wbeaty,  Thank you very much for the fix.  I had one of these on my bench and was baffled by the power problem.  I had spent alot of time tracing the power and then the lack thereof.  A quick search on Google turned up your posts.  I replaced the 2.2 uF cap w/ a 10 uF cap and it works perfectly.  I fix lots of lab equipment and have great experience, this expert honors the intelegence and help of others.  It saved me time.

Replaced the capacitor today, and it works!!  Thanks for posting!!

Hello Wbeaty and thank you so much for this thread.  I was presented with two 5415D's that would not energize following a prolonged power outage at Georgetown University.  I purchased four 47uF capacitors, two as backups, at my local Micro Center (wiped their stock out), performed the fix and all is well now.  As well as mounting the capacitors on longer leads - insulated, of course, I bent them back away from the regulator and also bent the regulator more away from the capacitor at about a 45 degree angle.   With all 3 'safeguards' in place - a higher value capacitor / capacitor bent away / regulator bent forward, I would think this to be a permanant repair.

Thanks again for your concise, detailed solution which saved my customer literally thousands of dollars!

Dave Heise

Laboratory Technical Support Services, LLC

Hello, I too have this issue with our 5415R. Working fine one day, then after power down, no display when you turn it back on. I replaced the 22uF cap, which was showing bad as per ESR meter.

Now, the unit turns on!! However, after displaying the model "5415 R" on the display, it immediately goes to "Error 17"?? Any ideas?