Aug 09 2017

Repairing the Melcor 390 Calculator Part 1 – An Exercise In Patience

So, after many many delays, I got the Melcor 390 calculator fixed. Oh, it was an absolute joy to get done soldering the capacitor in and finally seeing the LED’s fire up with “EEE1” and other garbage data, as this little calculator does when it’s first powered up.

If you don’t know what I’m talking about, check out these previous articles: I Got A Vintage 70’s Calculator, And Then It Blew Up! and Update On The Melcor 390 Calculator

Anyway, on to the repair process. I knew after asking online that the calculator had blown a tantalum capacitor, rated at 10µF at 16 Volts. Translation? The thing stored a somewhat tiny charge and was rated to handle 16 volts power – the calculator runs on 9 volts. The part, of course, was critical to the functionality, and beyond the circuit boards, the LED display, the keypad, and the integrated circuits, this was the oddball component that, of course, had to fail, but was easy to order, and order I did: a 10 pack for just a few dollars. I only needed one, but hey, that’s how these things go.

Normally packages take just a few days to get here, so I waited patiently, expecting to be able to repair the calculator in just a few days. I had actually ordered another unrelated package at the same time, and that arrived in a few days. These capacitors however, they took a ride.


Originally slated for August 1st, they finally arrived on the 4th. However, the USPS website thought they had been delivered on the 3rd, since that’s when they finally made their way “out” from the local post office. The thing is, they didn’t – it seems the package got lost time and time again during transit, not withstanding that it seemed to be tossed around the Memphis Distribution Center for about 4 days!

This is incredibly unusual, as normally I get packages in just a few days, as I said before. For it to take what seems like a solid week for me to get a small envelope carrying 10 capacitors. I consider myself a patient person, but even this took what felt like forever to me.

Still, on the 4th, they finally came. Of course, they would come while I was on my mini vacation, but they came finally.

In part 2, I cover the actual repair.

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