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Blown fuse and its soldering to a PCB

I need competent advice:

I purchased a new amplifier (Dared MP-60, made in China). It is cheap and rather good sounding, but its left side got dead (left-side tubes stopped glowing) when I replaced the stock 5881 tubes with RFT EL-34 (everything was OK for 30 min. but next morning, when I was switching it on, the problem appeared), though it was permitted by the user manual and was authorized by the seller.

When I opened the cover, I saw four 125V 8A fuses covered with opaque plastic cases. The fuses have leads soldered to the PCB. We measured them and indeed one was blown.

What is strange that the seller says "you can use unsoldered fuse, but there is no place to place a unsoldered fuse on the PCB". I asked for explanations ("Does it mean that the whole PCB must be changed or that the unsoldered fuse should be replaced by another fuse which should be soldered to the PCB?, and she said "Yes, there is no place to place the unsoldered fuse on the PCB, it means the whole PCB must be changed".

Is this PCB a single-use dummy (if it is possible in principle)? How can it be that the blown fuse must be unsoldered but the new fuse cannot be soldered to the same place in the PCB?
transl
12 responses Add your response
timrhu
2,779 posts
 
Solder in a new fuse if you can get in there. I can't think of any reason it can't be done.
The problem I have had is sometimes the heat from soldering destroys the fuse so be as gentle as possible. Also, leave the leads in place if possible. It's easier to solder a fuse to a lead that is in place. Good luck.
Ag insider logo xs@2x
stonedeaf
101 posts
 
When I serviced this stuff -always hated this.If it is possible -I would solder in fuse holders instead.BEFORE you do this -look at both sides of the board - is this going to even come close to touching another trace or component if you add holders? Something? blew this fuse - new tubes are definitely suspect - will be a real PIA if you solder a new fuse in and have to do it again in the next 2 min. or 2 days.I'm personally more than willing to desolder and solder components on a board BUT - pcb's are not really designed with this capability in mind.If you do this enough at one point on a board -you will pretty certainly have problems - the worst being the creation of a cracked intermittent foil trace.
Basically -if it's under warranty -I would return it for service and include the tubes you were trying to use.If the fault was caused by the tube - the importer will quit possibly charge you for the repairs.
timrhu
2,779 posts
 
Basically -if it's under warranty -I would return it for service and include the tubes you were trying to use.If the fault was caused by the tube - the importer will quit possibly charge you for the repairs.
Now that's good advice. I forgot we were discussing a new piece. Something I rarely own.
Ag insider logo xs@2x
stonedeaf
101 posts
 
Final note: Most service depts. will stock what are commonly referred to as "pigtail" fuses - these come from the factory with the wire already soldered to the end caps - much easier to use than trying to solder to the fuse without overheating it and blowing it before you ever get it installed.
transl OP
156 posts
 
Given that the shipping cost was $270....+ $270 back with the amplifier price being $492...I'd rather repair it locally... I talked to a technician and he said that it's betteer to solder the leads to the fuse holder. I'll get the fuse first and then will try to figure it out.
transl OP
156 posts
 
Stonedeaf:

I don't believe the RFT EL-34 tube was a suspect - this set worked properly with Cary SLI-80 and another manually biased integrated amp. My technician insists that an auto-bias function may create problems when installing vintage tubes...
transl OP
156 posts
 
Thanks a lot!

I will contact Partsconnexion or Parts Express for that.
rodman99999
6,130 posts
 
If you can't locate a pigtail type fuse: Find a plastic inline fuse holder, ie:(http://cgi.ebay.com/FUSEHOLDER-INLINE-FUSE-HOLDER-WITH-14Ga-WIRE_W0QQitemZ270366963842QQcmdZViewItemQQptZLH_DefaultDomain_0?hash=item270366963842&_trksid=p3286.c0.m14&_trkparms=72%3A1234%7C66%3A2%7C65%3A12%7C39%3A1%7C240%3A1318%7C301%3A0%7C293%3A1%7C294%3A50) and solder the leads to the PCB. I can't understand what the problem would be with de-soldering and re-soldering to a PCB. We've been doing it for decades, in the electronics repair business. That's what solder suckers and solder-wick are for. Here's an inexpensive kit: (http://cgi.ebay.com/SOLDER-SUCKER-DESOLDERING-PUMP-HIGH-POWER-WICK-SOLDER_W0QQitemZ220376267737QQihZ012QQcategoryZ46413QQssPageNameZWDVWQQrdZ1QQcmdZViewItem)
markd51
763 posts
 
Here's a real stupid, but simple fix, and might work for you? I did this once to a Sansui Reciever, that had a similar type blown fuse on the power supply board, and did this to sidestep mucho headaches.

Go to Radio Shack, get yourself some Fuse Clips. Solder two pairs of Fuse Clips back to back. You can then clip one side of the Fuse Clips to the Blown Fuse, and then clip in the new fuse on top "piggyback" style.

The paired clips, will look like two "U's" back to back when soldered together.

As long as it's the same value fuse, all will work just fine, and this will permit you to do a quick fix, without ripping out boards, or the worry of damage to the board from heat. Hope this helps, Mark
magfan
1,583 posts
 
Not all circuit boards are created equal.
Glass/Epoxy boards that I have seen are kind of translucent light green will take more 'rework' than cheesy cheap boards. I have no idea what the cheapo boards are made of, but when cooked it charcoals nicely and eventually becomes low-level conductive. Traces of these boards lift more easily, but can sometimes be repaired by laying a piece of bare wire where the trace WAS and soldering it to what remains good of the trace at either end.
While you have the amp disassembled for repair, it may be a good thing if you make all 4 fuses replaceable.
Marks idea is pretty cool, and may make sense in this case of what sounds like limited clearance.
fluxus's avatar
fluxus
1 posts
 
Hi,
I have your same amplifier, branded Fatman iTube 252, and just the other day I turned it on and half of the tubes weren't glowing, with one channel being off.

I am using it with some RFT EL34, Melz russian 6sn7-ish, siemens 12ax7.

I suspect it may be your same problem, one of the fuses (or more) being blown.

How did you finally risolve your problem? Do you have any tip to give me? I haven't open my amp yet.

If you even have old pictures you want to share, feel free :))

After you fixed (hopefully) your amp, did it last long without problems, or you did you ran into blown fuses or other issues again?

Thank you!
ozzy's avatar
ozzy
7,461 posts
 

I installed a fuse holder on the exterior of my Oppo 95.

Drill a small hole on the exterior of your unit , then just solder wires from old fuse wires to the outside fuse holder and "whala" your done.

You can then experiment with pricey fuses.

P.S.
Don't

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