Sunfire True Subwoofer Mk II Parts ID

[wrf 5,023]

I've acquired a Sunfire sub that should be scrapped, but I'm too stubborn to toss it out.  It suffered some sort of disastrous event that left transistors dead, caps swollen, an inductor that had one end lifted from the board and two so called jumpers that had been vaporized.  Of course there may be more damage I've not yet found.

 

But, I need help in identifying two components labeled JP1 and JP2.  I suspect they are fusible resistors of some sort, but values and wattage are a mystery.  I need enough info to order a pair.  The schematic available on the site here - called the "tracking downconverter  schematic" is about 90% accurate for the sub.  Unfortunately, there are not part numbers for JP1 or JP2.  I offer up the following photos.

 

1-  Schematic showing how they are used in the circuit

2- JP1 and JP2 in their original, unmolested state - photo courtesy of PMAT

3- Photo my board with JP1 vaporized and JP2 seemingly hanging in there

4- Photo my JP2 removed from my board next to a 1/4 resistor.  It measures open on a ohm meter.  PMAT measured .1 Ohms in circuit on his board.

 

Any suggestions would be appreciated.

 

 

 

 

 

 

 

 

[loner_t 2,568]

I can open one of my EQ10s, if that is the specific sub in question.

 

Bill Flannery may be another good resource to ask a question.  He is usually prompt and responsive.

[compwaco 1,129]

If it would be any help I can send you the amp out of one of my subs to help measure and compare to.

[wrf 5,023]

 

 

I can open one of my EQ10s, if that is the specific sub in question.

 

Bill Flannery may be another good resource to ask a question.  He is usually prompt and responsive.

 

Its  Sunfire True Subwoofer Mk II.  Thanks for the offer.  I may pester Bill if I run into a brick wall.  I'm a bit reluctant to bug him for DIY advice. 

[wrf 5,023]

If it would be any help I can send you the amp out of one of my subs to help measure and compare to.

 

Wow.  Thanks for the offer but this is really just a wild crusade to save a very dead sub that is suffering from a variety of problems.  I appreciate your offer. 

[RodH 4,866]

They look like solder in fuses. 0.1 ohm on a good one makes sense.

Digikey has them. As a last resort you could start with 2A and move up as work progresses? 

[danowood 2,167]

If I recall, James (retriever) was the sub guru on here, but haven't seen him around much for some time.

[wrf 5,023]

I believe Retriever has nailed this.  Its a zero ohm resistor.  You can tell because of the black stripe seen in one of the photos.  Black is zero in the resistor color code.

 

Based on the size I would have to guess it's 1/8 watt.  1/4 components are easily available at Digikey.  

 

One step at a time, and I'll have that sub thumping away again. 

[morris 390]

I have a MKII amp that doesn't work. I pulled out JP2 and measured 0 ohms, verifying that it is a zero ohm resistor.

 

You are welcome to use my amp if you need it. It's already out of the cube. 

[UncleMeat 1,173]

Watt's the difference between a 0 Ohm resistor and a 1/8W fuse?

[morris 390]

I was wondering about that too.. Fuses are rated in amps, resistors in watts.

It sure would be a lot easier to use fuse instead of a zero ohm resistor.

[wrf 5,023]

From my research, zero ohm resistors are essentially used as jumpers.  They have the added benefit of behaving like high amp safety fuses as well.

 

Consider this.  There is really no such thing as a zero ohm resistor.  Resistance is more like a few milli-ohms.  So -- for a 1/4 watt zero ohm resistor that is really a 2 milli-ohm resistor the following holds.

 

How many amps will this little beast handle before it vaporizes?

 

P = V * I

V = I * R

 

Substituting for V we get

 

P = I * R * I

 

Solving for I

 

I = sqrt(P/R)

 

Using P=1/4 watt and R=.002 Ohms

 

I = sqrt (.25/.002)

I = 11.18 amps

 

So -- our itty bitty 1/4 watt zero ohm resistor is really an 11 amp fuse.

 

Why not use a fuse? These are used for safety.  I.e.  Keep the house from burning, not protect the subwoofer.  Further, a zero ohm 1/4 watt resistor can be inserted on the board with the same machine that puts all the other resistors.  The same can't be said for an 11 amp fuse.

 

In the case of my poor abused subwoofer, BOTH the positive and negative sides of the output transistors were shorted. Direct short between high and low rail (depending on what the FETs were doing). Those little guys saved the board from having traces blown off.  Note that one of the FETs in the high rail is also shorted.  God knows what happened to this subwoofer, but it must have been exciting.

 

There is likely more damage.  I'll post later after I replace the dead semi conductors, zero ohm resistors and do a complete recap.  Several caps are completely shorted.   L2 - the inductor at the top was completely blown off its mounting points.

 

 

[UncleMeat 1,173]

Wow with all of that damage, what's the condition of the driver VC?

[wrf 5,023]

It LIVES!!!

 

Currently spread across the bench and probed in almost every possible way, the Sunfire Sub is alive and thumping.

 

I've learned a LOT and I'm still confused about the grounding inside this little monster.  But, it works.

 

Here's a scope trace that shows the output waveform and the tracking downconverter controlled rail voltages.

 

Not sure why it isn't tacking better, but that's a mystery to solve tomorrow.   Maybe at higher levels it behaves more nicely.

 

Once I'm sure it is working WELL, I'll write up all the parts that had failed and mistakes I made along the way. 

 

50Hz sine wave. 

 

 

[RodH 4,866]

House curve?