Little Mark II -Two Fuses Wrong Voltage

spcmstrbtasp · #1 04-15-2011, 07:47 PM

So- I've had a Little Mark II that up until yesterday has performed flawlessly since 2007, when I bought it new.

However, yesterday at a rehearsal it seemed to not have the headroom it usually does. To remedy I had to turn the input gain higher than normal (around 2 o clock) to closer than (3 o clock) and the Master to above 10 o clock instead of the normal between 9 o clock and 10. In addition it sounded 'boxy'. I tried to remedy this by turning off the filters, but that did not seem to help tone or headroom.

(Driving an 8ohm Bag End S15D)

So today I go to try to recreate the issue without the band, and to convince myself that in fact it sounded inadequate.

After about 10 minutes of playing, and immediately following an adjustment to the Master gain, the entire amp quit working- lights out- no sound.

My first thought- I wonder if I blew a fuse. In 4 years that hadn't happened but there's a first time for everything.

Much to my surprise I the fuse holder holds two fuses. I can quickly see that the filament on the first one is in two pieces. Thinking that the one in the back position is a spare, I place it in the front position and try to power up the amp again- nothing.

So I take it home to look up the manual online- or locate it in my files.
After reading it I see that for the US it specifies 8A 250V T .5x20. Looking closely at the fuses now...I notice that they are marked 8A 125V. but there are two of them. I also notice that the fuse I'd moved to the first position looks like an explosion took place inside it- blown for sure. So now I think that one may not have been a spare. (As I said- I'd not inspected the fuses in the entire time since buying new, so I have to assume these were original.)

Can someone please confirm whether or not this is the case?

Now, I'm wondering if I should a- attempt to replace the fuse- and if so what type 8A 125 or a single 8A 250....if such exists, and as the manual specifies.

Or b- Take it / send it to an authorized tech?

or c- give up and call it a door stop/ attempt to sell and recover value for the Markbass Bag. I've read a few posts that allude to the fact that we've entered the era of disposable amps...and I shouldn't expect more.

Any suggestions?

Spc.

In the meantime I'm happy I held on to my AI Clarus, which hopefully will get me through the weekend.

Bubba Ghanoosh · #2 04-15-2011, 08:24 PM

I just checked mine. Same as yours: 8A 125V.
That rating should be okay, as long as you're using the amp here in the US. (But, yeah, even on the fuse holder it says to use only 250V).

It looks to me like the 2nd fuse IS a spare. Nothing is contacting it when it is in the outer slot, and it is completely isolated from the other fuse.
When a fuse is in the inner slot, however, it gets pushed into position in the contacts (those two little metal brackets).

Did both fuses blow at rehearsal? Is the amp going through a surge protector, or directly into the wall?

spcmstrbtasp · #3 04-15-2011, 08:32 PM

It was plugged directly into the wall, but this is normal and has probably been done 200 times or more prior to yesterday without incident.

Thanks for checking and confirming the rating on your fuses.

I think I blew both fuses today. At rehearsal, I only heard the sub par tone and apparent lack of headroom.

Quote:

Originally Posted by Bubba Ghanoosh

I just checked mine. Same as yours: 8A 125V.
That rating should be okay, as long as you're using the amp here in the US. Actually, I think it's better, because it will blow faster than a 250V fuse. (But, yeah, even on the fuse holder it says to use only 250V).

It looks to me like the 2nd fuse IS a spare. Nothing is contacting it when it is in the outer slot.

Did both fuses blow at rehearsal? Is the amp going through a surge protector, or directly into the wall?

Bubba Ghanoosh · #4 04-15-2011, 09:10 PM

The 125V fuse is NOT better. But, it is adequate for use in the US (115V-120V). The 250V fuse provides better protection from arcing when it blows, but you shouldn't be plugging the amp into anything more than 120V anyways.

I would test the amp at home (or a different outlet), through a surge protector, using either an exact same 8A 125V fuse or the fuse specified in the manual.

If the amp still works, you should invest in a surge protector. You've got some really nice gear.

spcmstrbtasp · #5 04-16-2011, 05:54 PM

Thanks for the advice about the surge protection. You are right.

Now I need to track down some 250v fuses.

I wonder if Peter Murray still visits the forums and can confirm that either size is correct.

-Spc

Quote:

Originally Posted by Bubba Ghanoosh

The 125V fuse is NOT better. But, it is adequate for use in the US (115V-120V). The 250V fuse provides better protection from arcing when it blows, but you shouldn't be plugging the amp into anything more than 120V anyways.

I would test the amp at home (or a different outlet), through a surge protector, using either an exact same 8A 125V fuse or the fuse specified in the manual.

If the amp still works, you should invest in a surge protector. You've got some really nice gear.

billfitzmaurice · #6 04-16-2011, 08:42 PM

Gear intended for European use will specify 250v fuses because they run at 220v. Using a 250v rated fuse here, where the supply is 110v, is not of any particular benefit.

eastcoasteddie · #7 04-17-2011, 09:07 AM

Radio Shack should have those fuses...heck, they have fuses that I use on a power supply module for a $300K piece of industrial cooling equipment...

christw · #8 04-17-2011, 09:27 AM

Quote:

Originally Posted by eastcoasteddie

Radio Shack should have those fuses...heck, they have fuses that I use on a power supply module for a $300K piece of industrial cooling equipment...

and yet mine didn't have any pots worthy of bass guitar use when I stopped by yesterday.

Sneakypete · #9 04-17-2011, 09:54 AM

A fuse is a fairly crude protection device - just a filament that melts when it gets too hot. If yours looks like it's exploded - all black with little splatters of melted fuse on the inside of the glass it means it got hot VERY quickly! Don't worry about the voltage - with fuses it's always the current rating that's most important followed by the quick/slow blow choice. Hate to say it but it sounds like a power stage or output stage fault to me and definitely a job for an experienced amp tech. Good luck.

Funkinthetrunk · #10 04-17-2011, 10:05 AM

Quote:

Originally Posted by spcmstrbtasp

Thanks for the advice about the surge protection. You are right.

Now I need to track down some 250v fuses.
-Spc

Personally, I think it's time to find a tech....throwing in a 250v rated fuse isn't going to make this amp work again. Just my opinion.

spcmstrbtasp · #11 04-17-2011, 10:33 AM

I agree-

Experience with Markbass stuff may be hard to find.

Long out of warranty...I might just have a yellow and black paper weight/doorstop on my hands, if I what I've read about repairing these is true...

It was really good while it lasted. I wonder what happened to cause catastrophic failure.

Thanks for the input all.

Quote:

Originally Posted by Sneakypete

A fuse is a fairly crude protection device - just a filament that melts when it gets too hot. If yours looks like it's exploded - all black with little splatters of melted fuse on the inside of the glass it means it got hot VERY quickly! Don't worry about the voltage - with fuses it's always the current rating that's most important followed by the quick/slow blow choice. Hate to say it but it sounds like a power stage or output stage fault to me and definitely a job for an experienced amp tech. Good luck.

eastcoasteddie · #12 04-17-2011, 11:16 AM

Quote:

Originally Posted by christw

and yet mine didn't have any pots worthy of bass guitar use when I stopped by yesterday.

lol....yeah, pots are a different story....mine doesn't have any either...

spcmstrbtasp · #13 04-17-2011, 04:04 PM

And...Radio Shack only had up to 5A fuses... my luck is running out.

spcmstrbtasp · #14 04-17-2011, 06:10 PM

Can anyone suggest a source besides Radio Shack for 8A 250V or 8A 125V glass fuses for a Mark Bass Little Mark II?

Also, should I be looking for SLO BLO or Fast Acting fuses?

JimmyM · #15 04-17-2011, 06:13 PM

nothing wrong with the radio shack fuses. i usually use slo blos myself because i was told fast acting fuses are a little too intolerant of what amps do.

**Freddels** · #16 04-17-2011, 07:04 PM

RadioShack.com

http://www.radioshack.com/product/in...ductId=2103761

spcmstrbtasp · #17 04-17-2011, 09:09 PM

Quote:

Originally Posted by Freddels

RadioShack.com

8.0-Amp 250V 1¼x¼" Slow-Blow Fuse (4-Pack) - RadioShack.com

Freddels I saw those too, but...

Close, but not quite. The LM II OEM fuses are 20mm x 5mm, which is smaller than 1 1/4 in by 1/4 in.

5x20 is closer to 3/4 in.

Bubba Ghanoosh · #18 04-17-2011, 10:32 PM

I did some surfing and I think the "T" designator stands for a slow blo fuse.

You may have to order them. Try Digi-Key.

You can call or on-line chat for technical help.

Good luck.

JimmyM · #19 04-17-2011, 10:57 PM

Quote:

Originally Posted by spcmstrbtasp

Freddels I saw those too, but...

Close, but not quite. The LM II OEM fuses are 20mm x 5mm, which is smaller than 1 1/4 in by 1/4 in.

5x20 is closer to 3/4 in.

you're kidding! they can't even use standard size fuses?

BassmanPaul · #20 04-18-2011, 09:53 AM

If you have already blown two fuses with the amp no good will come of blowing a third and possibly more damage may occur. I too feel you have lost at least your output transistors. Is the bag End your normal cabinet or does it belong to your rehearsal place? Did you check your speaker cable between fuse changes?