[poormxdad]

Folks,
 
First post, but I've been here many times.
 
I have two pair of SR60s.  I honestly don't remember how old they are.  I'm using one with my digital piano.  Not bad, but I thought I'd try my hand at modding the second pair, which has been languishing in storage hell for several years.  Unfortunately, the left driver does not play.  I've jiggled the cable and the plug, but I get nothing.  Zero, zip, nada.  The right side plays fine.  I have the earcups open and can test the transducers with a multimeter.
 
With the meter set at 200k, the working driver shows 0.00 ohms, and the non-working driver 1 when measured across the solder joints.  Does that mean the driver itself is bad?
 
Thanks much,
 
poormxdad

 

[UnknownAX]

1. Set your meter to 200ohm. (=0.2k)
2. Measure from the base of the plug to the tip and the middle. (Be sure not to touch both of the probes while doing measurements.)
3. Measure both drivers.
4. Write down the values and post them here.

On working headphones all four measurements should show close to 32ohm. Using these measurements and a little logic you can tell what's wrong the the headphones. You should also repeat the first measurement on your working headphones to make sure the measurements are reliable.

 

[poormxdad]

Unknown,
 
As directed,
 
Base to tip  1
Base to middle  31.7
Base to left driver  1
Base to right driver 31.5
Right driver across the solder joint 31.5
Left   1
 
It's a cheap Harbor Freight multimeter, but should be good enough for yes/no answers.  What next?
 
Thanks,
 
poormxdad

 

[UnknownAX]

Apparently the left channel is shorted to ground instead of just being disconnected. It could be the plug, cable or driver. The plug would be the most likely place to cause a short like that. You'd need to disconnect one of the wires from the driver or plug to easily tell what the problem is...
With accurate measurements you could also compare the resistance at the plug and at the driver, but that isn't really possible with the short cable and resistance of the probe "connections".
The plug probably can't be opened, can it?
Do you see anything suspicious at the driver?

As you're already into modding them, you could "mod" the plug and solve the problem / find the cause for it at the same time... That requires soldering, though...

 

[poormxdad]

Sooooooooooooooooo, if I were to remove a wire at the driver and it measured good, that would tell me the plug or cable is bad.  If I cut off the plug and the driver measures good, I would know the plug is bad, and the driver and cable are good.  It would take me no time to cut off the plug and remeasure.  But if the driver still measures bad with the plug cut off, it's either the driver or the cable, and then I'd have to get a wire off the driver to be sure the driver is good.  Is that all correct?
 
What's the best way to disconnect the cable from the driver?  I have a decent soldering iron with several tips, but not much talent.
 
Thanks for your time,
 
poormxdad

 

[UnknownAX]

Yes, you can remove either the wire at the driver or the plug. If you don't want to change the plug for a different one, you'll have to try the driver first. The drivers of the sr60 look quite easy to solder, but there is always a risk of breaking them and the wire of the coil, which is attached to the soldering pad in some way, is seriously thin.
 
If you cut off the plug, you have to replace it. However, if the plug isn't the the cause, you'll have a bigger problem. Then you either need a new driver or a new cable. If the driver is broken then the cut-off plug is probably the least off your worries. And if the cable is broken (unlikely) , then the plug wouldn't be of any use anyway...
 
If you want to keep the plug, choose #1
If you don't want to (de)solder the driver and don't care about loosing the plug, choose #2
 
Quote:

 
What's the best way to disconnect the cable from the driver?  I have a decent soldering iron with several tips, but not much talent.
 

Choose a flat tip and heat the solder on the pad quickly. Pull carefully on the wire and it should come off. Try not to poke anything else with the hot iron.

 If the driver is constructed simply, the enamel wire of the coil will be somewhere in the solder blob, so be careful.

 

[Mad Max]

Grado drivers are easier to damage with heat than other headphones.  Make sure that the heat exposure is very brief.
 
Before anything, make sure that there is no flux residue on the left driver's solder joints.  A flux bridge can short left signal to ground.  Check first to see if that is the issue before anything.

 

[poormxdad]

 

Before anything, make sure that there is no flux residue on the left driver's solder joints.  A flux bridge can short left signal to ground.  Check first to see if that is the issue before anything.

 
I certainly will, but...  How could it be working and then have a "flux bridge" without human intervention?  Could it just happen?
 
poormxdad

 

[Mad Max]

   
I certainly will, but...  How could it be working and then have a "flux bridge" without human intervention?  Could it just happen?
 
poormxdad

 
Yes, it happens on rare occasion.  The "human intervention" was when it was assembled and wired.  The flux bridge can be removed by simply scratching it off with a small screwdriver, very little force needed.  Even a toothpick might get the job done, I think.  I've only ever done it with a screwdriver.

 

[UnknownAX]

A flux bridge on a driver resulting in perfect conductivity and complete silence from the driver seems highly unlikely to me. I don't know what flux grado has in their solder, but often flux is not conductive and can be left on PCBs. Even the conductive kind is not nearly THAT conductive.
Definitely take Mad Max's warnings about the drivers seriosly, though. Certain drivers (apparently Grado) can be quite sensitive to heat.

 

[Mad Max]

It is "highly unlikely".  That's why it is rare.  Flux is often not conductive, but becomes conductive over time quite often, which is why cleaning it up properly is essential, but slip-ups happen.  I've encountered such issues on headsets and regular headphones, resulting in silence or near silence or mono sound depending on the headphone design and where the flux bridge was located.

 

[UnknownAX]

I've heard that some fluxes can pick up moisture and thus become conductive over time so that might be the cause for flux conductivity in older equipment. Circuits on PCBs are probably much prone to this, though. Decent equipment is usually cleaned throughly, but the chinese hand soldered stuff often has nasty flux residues left on. The solder/flux I use can be left on according to the datasheet but i clean it if the part is installed somewhere or sold. Cleaning it is a sticky mess, though!

 

[poormxdad]

Alrighty then...  Yesterday I got out my magnifying glass and set about making sure it DIDN"T LOOK LIKE there was any flux shorting the driver circuit.  No change in the measurement.  I consumed several beers today and cut the plug off.  No change.  Soooooooo, I cut off one wire from the driver.  No change.  Then I cut off the other wire and pried the driver out of the cup.  That teeny, tiny copper wire does not seem to make it all the way round the driver frame to the solder joints for the cable  Does it disappear into the cup, or does it wrap around?  If that's obviously the problem, can it be fixed?
 
Thanks,
 
poormxdad

 

[kramer5150]

Not sure the quality level of the meter you are using, but yes it can make a difference... most specifically in the OEM probes that come with affordable meters.  For the longest time I refused to believe this until I finally bit the bullet and splurged on a better $25 pair of probes for the Fluke 179 my co-worker gave me.  Up to that point, with cheap probes (even with the Fluke) I was getting all kinds of "off" measurements that weren't making sense and  driving me nuts and into a tail-spin.
 
Set your meter to read Ohms and measure:
TIP-Sleeve should be ~31.5 Ohms
RING -Sleeve should be ~31.5 Ohms
TIP-RING should be ~63 Ohms, (its the two coils in series, grounded together through the sleeve contact).
 
Since you've got the earcups open, and have cut the wires off the drivers... measure resistance across  the solder pads on each driver, likewise it should be ~31.5 Ohms.  If it doesn't then you have an open circuit somewhere inside the driver.  Either the solder pad(s) have become disconnected from the tiny lead wires, the lead wires have broken, or the voice coil itself has developed an open circuit.  I don't know if there is an easy way to repair either of the 3 scenarios.  I had a KSC 75 driver where the solder pad became disconnected from the lead in wire.  I tried to re-flow solder and re-connect it, but failed miserably in that the heat from the flowing solder melted and disintegrated (for lack of a better term) the really tiny lead wire.
 
I have heard about loudspeaker voice coil repairs that involved "unwinding" a coil or two and using that newly exposed length to bridge over and re-attach to the lead wires.  I have never heard about anyone successfully doing this with a headphone voice coil however.  I tried it on a busted HD580 driver... with no luck at all.
 
At any rate heres some pics of Grado drivers...  You can see the lead wires under the diaphragm material.

 

 

[mol]

poormxdad,
 
When you measure across the pads of the non working driver and get a reading of 1, where is the decimal point on the display?
 
I have a cheap meter with a four digit display that reads 1 when the resistance is out of range or when there is an open circuit (as when the probes are not touching anything).
1 in the first (left most) digit, then two blank spaces, then the decimal point then the last digit (also blank).