Mark V Combo blowing fuses on power up - high voltage

[LPWallace]

Hey all. I'm having some trouble with my Mark V combo I wonder if I could bounce off you all. I've
had it about 2 years, purely home use and never leaves my little home studio, and it honestly doesn't
have a whole lot of time on it. I generally run it through a Rivera Rockcrusher Recording for direct
recording, so I think I'm out of luck on the warranty. Never been powered on without a load though.

Since I've had it, it's blown the fuse a couple of times, separated by a few months each time. I
raised an eyebrow, but didn't worry too much about it. A few weeks ago I turned it on (Full Power) and
it immediately made a loud hum and blew the fuse. Replaced the fuse, not too concerned, but when
powered on it did the same thing. Had one more fuse, replaced it and this time watched the tubes when
powering it on, but it blew immediately again with not the slightest light or flash from any tube.

I ordered all new power and rectifier tubes, and per the troubleshooting video removed them all and
powered it on, and it stayed on. Good. Put in the new tubes, powered it on and was going through each
channel testing, but about 15 minutes in on channel 3 I heard a hum. Turned down the guitar, but it was
still there and getting louder. As I turned down the volume on the amp it got very loud...clearly
internal...and the fuse blew. At this point I think I've done all the troubleshooting I can do on my
own, and it'll need to go in for service (sigh), but I'm curious if anyone has any insight or ideas.

An important question though. A few months back I got a new UPS with a voltage readout, and I saw
that my line voltage from the wall outlet was running kinda hot...averaging between 124-128 volts. For
a while it was even more, hitting 130-131 in the overnight hours, and the UPS was actually kicking in
and outputting 110v, presumable because of the high voltage. Could this have caused cumulative damage
to the amp? I don't think I'm getting large spikes, and I do have a lower end Furman power conditioner
in the rack that I power the amp from, but I'm concerned about the sustained high voltage.

I'm extra concerned now as I have a line on a really good deal on a Mesa Mini Rectifier for a
"backup", but I don't want to burn that up, or my Mark V after I (hopefully) have it repaired. Any
insight is appreciated.


Thanks in advance,

Larry

 

[jb's 52]

Sounds like you changed all the tubes and you're still blowing fuses.
At this point, service is in order. I'd bet that you will need the grid screen resistors replaced.

 

[bandit2013]

I would second that. I lost a screen resistor on one of the one of the middle tubes. However after the failure had occurred (caused by red plating tube) I knew by the smell of burning phenolic along with the smoke that a power resistor had been overloaded. I did not attempt to operate the amp until I replaced not just the one that split open but all of them with ceramic coated flame proof metal film resistors that had a higher watt rating. Your standard home solder iron will not do the job properly. I would not recommend doing this yourself unless you have the knowledge and skills required for repair work along with electronics background as well as proper handling of high potential circuits. If it still has a warranty get it done by an authorized boogie repair shop. The fact you still had a load on the OT should not void warranty. Were you using Mesa tubes when it happened? If so, do you still have the tubes that caused the fault? If so you may need to provide them for the warranty repair.

 

[Old BF Shred]

I agree that, if it is still under warranty, you should take it to a Mesa authorized tech and let them worry about it. Also be sure you have Mesa output (and perhaps even rectifier) tubes in it (in case you had ordered another brand) when you do, as they may tell you that using non Mesa output tubes will void the warranty. I would not volunteer that you were using an attenuator.
Good luck! 8)

 

[Authorized Boogie]

Your incoming line voltage is REALLY high...and can create all sorts of problems. The amps like to see 117V, and at the numbers you've mentioned a lot of current would be running things HOT!!

I agree that, if it is still under warranty, you should take it to a Mesa authorized tech and let them worry about it. Also be sure you have Mesa output (and perhaps even rectifier) tubes in it (in case you had ordered another brand) when you do, as they may tell you that using non Mesa output tubes will void the warranty. I would not volunteer that you were using an attenuator.
Good luck! 8)

I suppose this is one approach, but the more info you provide the more we can do to assist you... :roll:

 

[LPWallace]

Hey guys, really appreciate the replies.

Yeah it had the original tubes up until failure, and I replaced with new Mesa tubes. There were no signs of scorching in the sockets, and I never noticed any smell or smoke...just the loud internal hum.

Swapping tubes is about the extent of repair that I'll attempt myself. I've gotten into working on guitars a little, but have no desire or background to try to be an amp tech. I just want it to stay on and sound good (which the Mark V very much does).

What do you guys think about the hot input voltage? That's my immediate concern. It's not spiking, and I have the Furman, but input voltage to the amp is averaging 124-128 volts. I'm about to pull the trigger on a Mini Rec for redundancy (because I'm finding not having a working amp to be unpleasant , but if I have to get a true voltage regulator to protect the Mark V (priority) then I won't be able to afford the backup amp and will need to tough it out with amp sims.

 

[LPWallace]

@Authorized Boogie... I made a substantial investment in a nice little guitar rig centered around the Mark V for home recording in an apartment environment, and it was always intended that it was going to roar into a attenuator/direct box, and I'll just be up front with that and it is what it is. The most important thing now is protecting that investment, and you've answered that question. Thank you.

Ok, so voltage regulator it is. Anyone have any recommendations?

Really did want that Mini Rec though :-(

Thanks all

Larry

 

[Authorized Boogie]

@Authorized Boogie... I made a substantial investment in a nice little guitar rig centered around the Mark V for home recording in an apartment environment, and it was always intended that it was going to roar into a attenuator/direct box, and I'll just be up front with that and it is what it is. The most important thing now is protecting that investment, and you've answered that question. Thank you.

Ok, so voltage regulator it is. Anyone have any recommendations?

Really did want that Mini Rec though :-(

Thanks all

Larry

Unfortunately at that line voltage, you'd probably suffer the same result with the Mini-Rec. Its imperative to get that voltage under control! Thanks!

 

[Authorized Boogie]

You may have another blown tube...so be aware of that.

Next time, run the amp on Variac power until you can get a handle on the wall voltage : )

 

[LPWallace]

Yeah I figured one or more of the new tubes would be blown...I'll let the tech sort that out.

You said that optimally the amp is looking for 117v. Would a solid 120v be safe? (looking for super-safe here).

http://www.sweetwater.com/store/detail/P1800AR

Appreciate the help

 

[Authorized Boogie]

Yeah I figured one or more of the new tubes would be blown...I'll let the tech sort that out.

You said that optimally the amp is looking for 117v. Would a solid 120v be safe? (looking for super-safe here).

http://www.sweetwater.com/store/detail/P1800AR

Appreciate the help

Yes, 120v is most common before the is any draw on the incoming. Safe : )

 

[elvis]

Reasonable power mains design should handle nominal +/-10%, or up to about 127V in the US according to NEMA.

http://www.pge.com/includes/docs/pdfs/mybusiness/customerservice/energystatus/powerquality/voltage_tolerance.pdf

The million-dollar question, though, is what are your mains really doing? Using a handheld RMS meter will give you some sort of average reading, but doesn't actually tell you what is going on. For example, you may be getting a pure sine wave at 126VAC and the meter may show 124-128VAC due to noise.

OR

You may be getting 120VAC plus some lovely 30V transient spikes from a motor or compressor on the same line.

You'd really want to look at the line voltage with either a decent oscilloscope or spectrum analyzer to diagnose. The meter will do its best to average whatever is there, but it's only so good at it. The mains may be so bad that they damage a voltage regulator :shock:

 

[Monstercastle]

Reasonable power mains design should handle nominal +/-10%, or up to about 127V in the US according to NEMA.

Exactly spot on. Saying the amp is designed for 117V is a bit of a generalization and not very realistic. My various meters around my electronics typically sit between 121-126 most days out of the summer months.

 

[LPWallace]

Just pulled the trigger on the Furman P-1800. While it doesn't seem to fluctuate more than 2-3 volts at any given time, over the last few months I've seen readings drift from 118 - 131v. Even if the meter on the UPS isn't totally accurate, it doesn't appear to be very stable. With another pricey amp coming in (yeah, I'm still getting the Mini Rec I'll make a further investment in good power to protect it all.

@elvis

Now you've got me concerned about damaging the voltage regulator, an expensive piece of gear in it's own right. I'm in an apartment in a private house, and while I'm coming off my own breaker box, the landlord does have a lot going on here (big multi coy pond arrangement out back, a lot of pumps and lights and such). The P-1800 seems to have good specs with regards to what you mention:

- Operating Voltage: 90 to 139 VAC
- Over-Voltage Shutdown: 140 VAC Nominal
- Approximate Input Voltage Capture Range: 97 to 137 VAC
- Spike Protection Mode: Line to neutral, zero ground leakage
***- Spike Clamping Voltage: 188 VAC peak @ 3,000 Amps***
- Response Time: 1 nanosecond

Do you really think it's possible that I may have issues that could burn through the voltage regulator? My knowledge of power/electricity is admittedly minimal. If I were to engage someone with the tools and knowledge, could you suggest the kinds of things I'd want to ask them to look for and address?


Thanks everyone for your help.

Larry