Crate Blue Voodoo 120 tubes not glowing.

[SenorHizzle]

Turned my BV120 on at practice yesterday, and had no sound output. I could see behind the front grill that the tubes and the orange back lights were not glowing. All of the front panel indicator lights, Power and Standby switches are on as normal.

I was able to open the amp and at least remove and test the fuses and all were ok. But that's as far as I was willing to go since I am not sure how to properly discharge the evil cap and dive in further. I have a fair electronics knowledge. I can wield a soldering iron, use multi meter, and follow schematics to a point and have built a few homemade effects, rewired guitars etc..

Anyone have suggestions where to go from here? I'm not sure at what specific points I'm needing to test and where to place the probes so that I'm testing accurately.

Thanks in advance!

[mozwell]

First check the fuses again, power off, remove each fuse & check it with a multimeter
F1 is 2.5A slow blow for 115V supply, 1.6A slow blow for 230 / 240V supply
F6 is 6.25A slow blow
F2, F3, F4, F5 are 0.25A normal fuses

Next check the power supplies, power switch on, standby switch off
Voltage on each side of R97 to 0V, one side is +14V, the other is +10V
Voltage on each side of R98 to 0V, one side is -14V, the other is -10V
Voltage on each side of R104 to 0V, one side is -80V, the other is negative (bias volts, maybe around 50V ?)

Voltage across R106 and R107, do you get 3VAC on each
Voltage across R113 and R111, do you get +3VDC and -3VDC

If these are all ok, then with power off, pull V1, power back on & measure DC volts between pin 4 & pin 9, should be 6VDC
Repeat for the other valves
V2 has DC heater
V3, V4, V5, V6, V7, V8 have AC heaters

With power off, Check any wiring connectors that plug into boards, unplug them & then reconnect them. Check any wiring that pushes onto a quick connect tab (or similar) are these tight

Post measurements here & we can find out where your problem is

Note there are high voltages in this amp, which can kill if you are not careful. TAKE CARE !

[The Dude]

In addition, check that the fuse holders are not cracked loose from the circuit board. These amps are notorious for cracked/cold solder joints. Look everything over carefully.

[Leo_Gnardo]

All tubes not lighting, or just the output tubes? The output tube board on Blue Voodoo's is mounted on a couple of multipin connectors and I've sometimes found the pins/sockets that handle filament current on those to be roasted, corroded, and not conducting as they should. In those cases I cut off the offending pins and fly a couple of wires from the main board filament traces to those on the output tube board. No skinny wire if you do this, 16 or 18 gauge ought to do the trick.

BV's a good sounding amp, worth the effort to make it work.

[Enzo]

Yep, just a couple days ago, I had a BV120H with half the power tubes and lights dead. That inline connector wasn't doing the job, so I ran a couple wires from near the heater power entry up to one of the bulb socket pins, very convenient for that.

[SenorHizzle]

Fantastic information!! I will troubleshoot and see what info I can get this weekend as soon as I can get the amp on my work bench!

[SenorHizzle]

**Current Update.

So far I pulled all the fuses again and tested them. The 10A Slo-Blow that bridges the heater circuit was blown. I tested it before and must have gotten a false positive reading. So, I replaced the "hard to find since RadioShack is now gone" fuse, and powered on the amp. 2 of the 4 power tube back lights on the right side on the amp lit up for about 2 seconds, and then went out.. None of the other tubes showed signs of life. I then powered down and checked the fuse, and it was blown.

I then decided to remove all the preamp and power tubes and power it up again with a new fuse. I had read on another board a bad tube may cause the fuse to blow. I observed the same result with all tubes removed. The same 2 backlights came on, and then off after almost 3 seconds. All other power and indicator lights on the amp are on, the channel indicator LED is on and switches as it should. so it seems to me (with my limited knowledge) that so far it appears to be an issue with the heater circuit. But, with that said I have not had a chance to place a meter on the points mentioned in the first reply. I was truly hoping this was just a matter of bad power tubes.. Seems likely it's something more sinister and costly.

[g1]

What are the backlights for?

The heater winding also powers the bridge rectifier for the DC heater supply (preamp tubes). There may be a problem there. D19, D20, D21, & D22.

[SenorHizzle]

I assume backlights are for aesthetic purposes. The BV120 comes with orange capped lamps, but I have Blue bulbs in mine cause of course, it's a Blue Voodoo. Plus it matches with my frankenstein'd guitar that I added blue LEDs to the neck and inside the body. That guitar is my profile pic. Has a clear Plexiglas pick guard, and the inner cavity is painted chrome.

I'll check out the bridge rectifier the best I can. I'll look up best way to test since not as familiar with it.

[Enzo]

There is the row of 6L6 tubes, and behind each one is a #44 or #47 6v lamp with a colored shield over it to provide an orange glow through the tubes. Strictly cosmetic. The bulb sockets are on the pc board with the tube sockets.

If it is blowing that fuse with no tubes installed, then dismount the power tube board. You have to unscrew the tube sockets I believe, and maybe another screw or two, but no mystery, then the board is plugged onto the main board by two rows of connector pins. If the fuse no longer blows, then the tube socket board has the short.

Oh, and before that, the first couple tubes use DC heater current, and there is a bridge of four 1N4007 diodes across the 6vAC, so check those for shorts, as well as the 4700uf ccap that filters the supply there. Oh, g1 already said that.

[SenorHizzle]

I tested the diodes D19-D22 in circuit with the diode setting on my meter. From what I could tell, they were working correctly. I read different postings about In -vs- Out of circuit testing and results can vary... I also used a continuity tester on them to see if was reporting a short. I also tested the resistors R111, R113, R106 and R107. They tested fine as well. SO I will do what Enzo has suggested next and remove the tube socket board and see what I can get. Though, with that removed there is no visible indicator that the circuit failed where as before I was seeing the backlights. But, since I know the circuit blows after 2-3 seconds, I'll power off and test the fuse. I'll inspect the socket board for shorts as well. I do need to test that cap C63 too. I didn't pull the board out this time to get to the solder side. Took me about 15 minutes just to get the glob of silicone off of the D119 and R113 next to that C63 cap!

[g1]

It's also a possibility there is a short in one of your lamp holders.

[SenorHizzle]

Good point. Could even be a bulb causing the problem. I'm fairly certain that flames will shoot from my head if it turned out was a bad bulb.

[g1]

In such case, please be sure to post pics .

[Enzo]

With the tube board pulled, there still is a visual indication. You no longer have the bulbs to see, but you do have a fuse that was blowing. Look at that, did it still blow or not. That is the visual indication.