Help - BV120H - Nothing, no power, nada, zilch, ideas?

[trip]

Hey Guys,

Hoping anyone can give some insight on this, if it's a common failure or if any one has seen it before, I know Enzo is on here and he knows all so hoping I can get some guidance.

Quick background, amateur at this stuff, I think it's fun to pick up broken tube amps and fix them. I would love to learn everything there is to know but I'm not at that level yet. I've fixed a handful, less than 10. I know enough for safety, but my troubleshooting practices are limited, most problems have been visual or obvious so far.

Grabbed a BV-120H for cheapp, I know there's a lot of bad talk on this series but for 70 bucks with 8 new tubes you can't go wrong.

Low and behold I get NOTHING with power up. No indicator light, nothing reaching the tubes, basically dead. The 5a slow fuse right in front of the power is good, the 10 amp is good, there's 4 .25 amp fuses, they all test good although one looks a bit bronze, is it possible that one of these .25 amp fuses would cause nothing to work? Seems a bit far down the electrical path.

I also see other pics on the internet where I see 2 blue wires coming from the OT but mine only seems to have 1, from what I read I'm pretty sure that's only used for wiring to something other than 110 but I'm not 100%, I don't know if this one wire could be the cause.

Visually this thing seems really clean, nothing looks burnt or out of place.

It's just dead and I'm not 100% on where I should be looking but I want to figure it out.

Anyway, best advice on how to start trouble shooting this issue? What/where should I be using my meter to follow and find this issue? I'm really into this stuff and passionate about learning, and would appreciate any help.

Attached is a crappy picture pointing out where I'm not seeing the blue wire since I'm not around it atm. Will update with better later.

Any insight on this? Is it a common issue with the older bvs? I'm hoping/thinking it's an easy fix, this thing looks great inside to my amateur self at least.

[Leo_Gnardo]

First of all, let us know what the hellza BV .... oh Crate Blue Voodoo, now some folks might know about those.

No power getting anywhere? Check line fuse. Check power switch. Check AC cable. We hope the power transformer hasn't failed. That's a possibility but DO check the easy cheap-to-fix things first. Wouldn't it be nice if you found a solution there, sure would relieve a lot of panic.

Further in, you'll notice the Blue Voodoo has an unusual feature, the circuit board holding output tube sockets is attached to the rest of the world thru multipin connectors at each end. These are a source of problems, not to say your BV has 'em. Heat and corrosion do their dirty work here, and in some cases I've found output tubes getting no filament power because the multipin connectors handling filament current are roasted. In those cases I've run separate wires from the tube sockets to appropriate connections on the main circuit board.

In spite of their hassles, Blue Voodoos are good sounding amps when they're running right.

[The Dude]

Yes, do all of those things Leo suggested. Also, check the AC voltage across the white and black PT wires (primary). Post here. Then check (with power switch on and unit unplugged) resistance across the blades of the AC cord. Post here. Don't worry about "common issues". We just want to troubleshoot it like anything else. Also don't worry about the OT just yet. We need to find power first.

Schematics here:

http://music-electronics-forum.com/a...37-105xxh1.pdf

http://music-electronics-forum.com/a...0-29512h0_.pdf

http://music-electronics-forum.com/a...16-105xxp2.pdf

[trip]

Appreciate the help guys.

Unfortunately I don't have an area where I can leave my stuff out anymore so it might take another few days to get back to it (don't want to come home to stuff more broken than before)

The line fuse is new, the 10a is also new, all 4 .25s seem to test out good too, might replace one of those 4, the d plug is verified working too.

I'll definitely check the voltage across the PT mains and post here afterwards, kinda hoping it reads out normal so it's a simple fix (would suck to buy a new PT for more than the I got the whole enchilada for haha) Hoping this one will teach me a lot more about diagnosing, everything before has been mostly aided by visually broken components. Everything pretty much looks flawless in here to me, I could be wrong but idk if the blue LEDs are stock for these original ones, nothing on the board looks modified but I also didn't take it fully out of the chassis yet to look at the other side (knobs amr?)


Quick question, what is the proper way to test the power / stand-by switch?

Will report back after testing the voltage through the pt primary. I should be aiming to see the standard 120 ac right? (Alligator clips and one hand in the pocket!)

Thanks guys!

[trip]

Alright so I checked for ac volts across the white and black pt wires and I got absolutely 0, plugged it in turned it on and nada. I also took the resistance across the blades of the ac chord and it looks ∞... what else can I do to be sure it's the PT?

Yes, do all of those things Leo suggested. Also, check the AC voltage across the white and black PT wires (primary). Post here. Then check (with power switch on and unit unplugged) resistance across the blades of the AC cord. Post here. Don't worry about "common issues". We just want to troubleshoot it like anything else. Also don't worry about the OT just yet. We need to find power first.

Schematics here:

http://music-electronics-forum.com/a...37-105xxh1.pdf

http://music-electronics-forum.com/a...0-29512h0_.pdf

http://music-electronics-forum.com/a...16-105xxp2.pdf

[Leo_Gnardo]

Alright so I checked for ac volts across the white and black pt wires and I got absolutely 0,

That tells us power is not reaching the power transformer primary.

plugged it in turned it on and nada. I also took the resistance across the blades of the ac chord and it looks ∞...

Still leaves AC cable, fuse, fuseholder as suspects.

what else can I do to be sure it's the PT?

Break out your ohm meter. Measure the PT black & white leads. If you get continuity, maybe a couple of ohms then your PT is probably good and the problem elsewhere.

Measure AC cable blades to AC cable connections inside amp. And measure across the fuse holder. Might be all you need is a new plug on your power cable, that sure would be better than replacing the power transformer and finding you didn't need to do that, right? Internal breaks in power cable also commonly happen a within a couple inches of the chassis.

[trip]

hmm I get 1.2 ohm between the black and white leads w just resistance (still hooked up to the board)
from the blades to the internal plug i'm getting .1 on all 3
about 1 ohm reading w conintuity between the b & w leads

i'm getting continuity between the black and white, plug leads, fuse holder

although i'm not getting continuity on the diode bridge D6 7 8 & 9 ,
i am on D 11 12 13 and 14.. but not 6 7 8 & 9.

getting it across the stand by switch between j26 and j44, beeps on off as i flick the switch, same with power switch between j31 and 33 so those seem to working,

but from end to end on any of those d6 d7 d8 or d9 diods i don't read continuity, they don't look burnt but is this leading me to think that bridge failed? (had this exact issue happen in a second hand 65605+112 but they did look slightly tinged)

am getting 121 ac between the ac plug so it's getting there

That tells us power is not reaching the power transformer primary.



Still leaves AC cable, fuse, fuseholder as suspects.



Break out your ohm meter. Measure the PT black & white leads. If you get continuity, maybe a couple of ohms then your PT is probably good and the problem elsewhere.

Measure AC cable blades to AC cable connections inside amp. And measure across the fuse holder. Might be all you need is a new plug on your power cable, that sure would be better than replacing the power transformer and finding you didn't need to do that, right? Internal breaks in power cable also commonly happen a within a couple inches of the chassis.

[Leo_Gnardo]

Crikeys, one of those cases where it looks like "all systems go" but it's not. You said no pilot lights either. Sometimes the ones inside switches fail so we can't count on them as reliable indicators of "power's on."

Let's see if power really is getting to the PT primary, set your meter for AC volts, clip your test leads to the power transformer's primary leads. Plug in, switch on, 120 VAC shows up or no? If yes then check voltages on the secondary taps, one set at a time.

[DrGonz78]

What about testing continuity from, I think it's the hot blade, AC hot input on amp to the fuse holder. It's the side that has ICL1 between power input and the fuse holder. I think ICL1 is a thyristor that limits inrush current on turn on. Perhaps that component is open or the solder connections have failed.

i'm getting continuity between the black and white, plug leads, fuse holder

Perhaps this statement needs better understanding on my part but reading it confuses me a bit.

[The Dude]

What Gonz said. I can't remember for sure. Is this one of the amps with a little circuit board where the IEC connector solders in? If so, pull that board and check all of the solder joints. Often, the input AC connections crack loose. There's also a thermistor there that comes loose. Sometimes, they even fall out and are rolling around in the chassis.

[Enzo]

If you don't get 120vAC right at the primary wires, then nothing on the rectifier side is going to matter.

You have continuity through the primary, but not through the mains wiring. SO go back and check the switch, the fuse/holder, any thermistor, and the wiring. And as Dude said, check for broken solder on the IEC connector.

[trip]

---Let's see if power really is getting to the PT primary, set your meter for AC volts, clip your test leads to the power transformer's primary leads. Plug in, switch on, 120 VAC shows up or no? If yes then check voltages on the secondary taps, one set at a time.

Nada, if I hook the leads up to the white and black while connected to the board and turn it on I get nothing, should I be doing these readings with the PT disconnected from the board? if i clip and read from one side of the ac plug and the other end on pretty much any component I get ac wall v but not up by the removable board the power tubes sit in,

better even, I don't even see this thermister there, I can't find the best pics online of other guts but I'm pretty sure it's not there, though I don't see a placement on the board for it, and I

[olddawg]

---Let's see if power really is getting to the PT primary, set your meter for AC volts, clip your test leads to the power transformer's primary leads. Plug in, switch on, 120 VAC shows up or no? If yes then check voltages on the secondary taps, one set at a time.

Nada, if I hook the leads up to the white and black while connected to the board and turn it on I get nothing, should I be doing these readings with the PT disconnected from the board? if i clip and read from one side of the ac plug and the other end on pretty much any component I get ac wall v but not up by the removable board the power tubes sit in,

better even, I don't even see this thermister there, I can't find the best pics online of other guts but I'm pretty sure it's not there, though I don't see a placement on the board for it, and I
[ATTACH=CONFIG]42681[/ATTACH][ATTACH=CONFIG]42682[/ATTACH]

What he said. There is another old tried and true test bench tech test that I'm hesitant to tell you to do. We used to call it a suicide cord. It's an AC cord (preferably with the high side fused) that you either clip or temporarily solder to the PT primary. It bypasses everything up to the primary and allows you to see if there are additional problems. I used to have several of them with different valued circuit breakers. The advantage is as a bench tech it saves you time if a unit has multiple problems or is missing it's weird detachable AC cord.

[Enzo]

He doesn't need a suicide cord, though it would work here.

The IEC connector for the mains cord has exposed terminals in back. Have you tried a different power cord by the way? Plug the amp in, is ther 120vAC at the two main terminals on the rear of the IEC connector? When you turn on the main power switch, does it light up?

Look at the schematic, the mains circuit is simple. The black and white transformer wires plug onto the board at push-ons J35, J36. Do they in fact connect to those two? Now from the IEC connector, the neutral goes directly to J36. The hot goes through a thermistor, which is right beside the fuse holder. Though your board appears not to have had one, in which case the hot mains lead runs to the fuse holder and out its other end to J31 for one end of the power switch. The other end of the switch is wired to J33, which is a direct shot to J35.

I hope you have a good mains fuse in there and of the proper value. But a good fuse is no guarantee the fuse HOLDER is OK.

[DrGonz78]

I am thinking this might be the thermistor but it is hard to see in the pic.