Crate Blue Voodoo 120 tubes not glowing.

[SenorHizzle]

In theory, that would work, but it's a ceramic fuse.

[Enzo]

Fair enough, then we pop the fuse from its holder and check it with a meter.

[SenorHizzle]

Bulb sockets checked out fine. The bulbs themselves also were testing good. I didn't have a chance to get into much yesterday.. but one really odd thing I noticed, before I did any testing, I removed the fuse and placed my meter across the fuse holder and tested for continuity, and It tested positive. That didn't seem right to me at all. I then removed the Power Tube board, and tested again. This time, no continuity. I then went over that board with a magnifier and bright LED light looking for any sort of short, or bad solder trace.. anything that could be causing it. I found nothing again. Pulled out the main board next and did the same thing on the solder side near the fuse holder and all the surrounding components. I followed the tracings from that to the Power Tube board connectors. Still didn't see any issues. I think trying to fix this thing is making me mental! But i'm determined.

[g1]

but one really odd thing I noticed, before I did any testing, I removed the fuse and placed my meter across the fuse holder and tested for continuity, and It tested positive. That didn't seem right to me at all.

Not sure what your meter considers "continuity", what was the ohms measurement? Some resistance will be normal due to R106 & R107 and other parallel circuitry.

[Enzo]

If the tubes or bulbs were in place, that would explain the continuity. If not, then something is shunting the supply. At that point flip the meter to ohms. There is a big difference between zero ohms and say 50 ohms, but both will show as continuity. If pulling the tube board stops the issue, leave it off and measuer across the bulb socket pins, two are one circuit and the other two are the other. If one pair of sockets shows low resistance but not the other, then that low one is the side with the issue. Of course, no bulbs in them.

[SenorHizzle]

Ok, I see what your saying about the parallel circuits reading. The continuity option Is on one of my meters, it's a pocket digital multi meter I got from Radio Shack back in 1995 when I was working there. It's been my #1 goto for easy testing. I believe that it's using Ohms functionality? Gives an audio beep to confirm continuity.

[Jazz P Bass]

It would help to keep in mind the limits of your tools.

Continuity test is great if you are looking for 'is it there'.
It may even be a diode test function.

Reading the actual resistance is much better when troubleshooting a problem.

As Enzo stated, the difference between zero ohms & 50 ohms can help lead to the problem.

[Enzo]

And a word about testing fuses in their clips. Follow me here:

When a good fuse is in the clip, we have a complete circuit. Your transformer winding has very low resistance itself, and the tube heaters, especially a number of them in parallel (plus even some parallel light bulbs in your model) have a total parallel resistance of not much as well. with the fuse out though, if we measure across the open clip (or a clip with an open fuse in it), the one probe of our meter sends its test current through the winding, out the other end of that, then through the tube heaters, and arrives back at the other end of the fuse clip to your remaining probe. The transformer and tube heaters do not add up to more than a few ohms, which looks to your meter like continuity. SO making that measurement at the clip can fool you because even a blown fuse will show a low resistance reading. That is why we MUST pull the fuse from its clip to check it.

[SenorHizzle]

Removed the Power Tube board, popped in a new fuse. Powered on for about 10 seconds. Disconnected the power, pulled the fuse out to test, and was blown. So something on the main board is still my problem. Again, I will trace out the leads and solder points that run from the circuit. I still haven't ruled out that the power transformer could be the problem sending bad voltage\amps out the 6v leads that plug into the board.

[Enzo]

No, the power transformer is not blowing the fuses AFTER the power transformer. Don't blame your car for taking the wrong exit off the freeway.

[g1]

The schematic does not show us which of the components in the heater circuit are on the power board, and which are on the main board.
You will have to tell us or post more pictures.
TR1, and the rectifier and filters for the DC heater supply, are they on main or power board?

edit: I guess the drawing called "tube bd. schematic" shows everything that is not on the main board?

[g1]

Preamp tubes V1 and V2 get heaters from DC heater supply, but V3 and V4 run off the main heater supply so that's something else to look at.

[SenorHizzle]

It's Alive! I traced down every solder point, every component that was near any point of contact, every connection and anything else I could get into.. and found nothing. Not a single bad solder joint, bad trace or loose connections. Then frustratingly I figured i'll put it back together again, pop another fuse in, and turn it on just to see if it blew like it has done 4 other times... and it came on!! Tube were on, back lights were on! Next step is to plug in a guitar and make sure it's all good. That's my current update. Electronics are some quirky devils! One bonus is though, I have REALLY sharpened my intermediate electronics skills on this one! I think I missed my calling, cause love tinkering with electronics, should have just studied that instead!

[g1]

Were you using slow-blow fuses all along?

[SenorHizzle]

yes, bought the exact match fuses. Made sure to buy slow-blow. Who knows, they could have had them mislabeled?? Bought them from my local Radio Shack franchise store.