GT-101 Troubleshooting Hints

Most customers assemble their GT-101's and find first time success. I guess you've visited this page because Edsel Murphy, author of "Murphy's Law", has visited you and your GT-101. That unsavory son-of-a-gun visits us all at one time or another, so as Bill Clinton used to say, "I feel your pain". Here are some hints to get your newly assembled GT-101 fully working.

Common Problems

In no particular order, here are some of the problems that have been reported:

power supply pcb assembled closeup

amp pcb assembled closeup

Blown Fuses 1

120 Volt Fuses

The original batch of GT-101's shipped with fast blow 3.15 Amp fuses. Those have proved perfectly adequate for 90% of the amps, and perfectly frustrating for 10% of the amps. The problem is that the fast blow fuse has a marginal I-squared-T rating given the rather large input capacitor. A more appropriate fuse would be a Medium Acting, or in the limit, a SLO-BLO 3 Amp fuse. If you're having trouble with occasional fuses blowing, this is a cause that should definitely be checked out and eliminated. If you need the medium or slo-blo fuses and can't find them locally, send an email to I can send registered owners of GT-101 the correct fuse by first class mail. But, please read Blown Fuses 2 first.

240 Volt Fuses

Yes, I made a similar mistake on the 240 Volt version of the GT-101, shipping 1.5 Amp fast blow fuses with those, too. It was only recently brought to my attention. A proper and robust fuse for 240 Volt operation would be either 1.5 Amp or 1.6 Amp Slow Blow fuse. An example of the 1.6 Amp slow blow fuse would be Schurter P/N 0034.3119.

Blown Fuses 2

Another source of blown fuses is an inadvertent swap of C6 and C7 on the power supply. The two look similar, but have rather different capacitance and voltage ratings, and are not interchangeable. The following picture shows correct installation. If you've swapped the caps, you will surely be blowing fuses.

check for correct power supply cap installation

Fuse Identification

The fuse type is marked on the end-caps. If you're over 42, you may need a good light and a Jewler's Loupe to read the marking. Here's a quick table of the markings that you might see.

While not foolproof, you can also get a pretty good idea of the fuse type by judging the thickness of the fuse wire. The Fast acting fuse has the thinnest, straightest wire. The medium acting fuse has a heavier, somewhat curly wire. The Slo-Blo fuse has a heavier and tightly coiled wire. These three variations are shown in the picture below.

fuse identification

Volt-Ohm-meter Checks

Visual Checks


Are you tired, hungry, or upset? Go away from the problem, take a nap, have a bite, and calm down. I know this may seem condescending, but I have solved many problems quickly after taking a break. Sometimes you can be too close to the problem to see it clearly.

Confessional Debugging

Explain the problem and what you've done to anyone. They don't have to be technical. It could be your spouse, your kids, your dog or cat. Sometimes just the act of explaining your situation aloud leads you to the solution.

In case none of that works

Take the best possible pictures you can of whichever assembled PCBs (both sides if possible, but certainly from the component side) are giving you trouble. Include pictures of the I/O connectors. Send the pictures with a description of the problem to I'll look at them, and usually we can find the problem inside of a few email exchanges.

If we can't get to the bottom of the problem by email and pictures, we can arrange a Skype session.

If none of that works, we can make arrangements for you to send the module in question in for trouble-shooting. If the problem resolves to a bad component, there is no charge for trouble-shooting or mailing. If the problem is caused by a soldering problem or swapped components, then you'll pay shipping both ways and a $25.00 repair fee for each module submitted for repair. We reserve the right to refuse to repair a module if its construction has made it impractical to do so. In that case, you may choose to purchase a replacement module in either kit or assembled form, assuming they are available at the time of your request.

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