Troubleshooting clarity - both L + R panels DOA

[wfissell]

Hi,

Bought a pair of clarity (craigslist) for not much money and in that context unable to test. Turns out neither electrostatic panel is doing much so I can't learn much from the swap-panels-and-see-if-its-the-panel test. Have query into ML service but thougth Id ask here if there are low-voltage test points I can measure to distinguish power supply from audio transformer.

I read a lot of about dust and ES panels. I have no idea the provenance of these. Any diagnostic/therapeutic cleaning I should/should not do?

- blue LEDs on, off appropriate to sensing music
- no change with changing/swapping powersupplies.
- woofers and the little rear-facing tweeters doing fine.

Will take the panels off in a bit and sniff around.

Thanks in advance.

 

[JonFo]

If the blue light is on, then the power supplies and music sense seem to be OK.

My first guess is that a prior user hooked them up to an underpowered receiver, turned up the volume, and fried the step-up transformer in both units (and likely his receiver). Square waves (distortion) are not good for items in an audio path.

So you will need to test the voltages going into the transformer and those coming out, and if nothing (or less than input), then the tranny is toast. Remember to adjust the voltage selector on your meter to a 75x level when measuring the output.

And to make sure you don't repeat the same issue once fixed, what amplifier do you have for them?

 

[wfissell]

Hi, thank you.

What sort of voltages are on input and output? I have an oscilloscope and can have a looksee at actual numbers and waveforms, but before I get an unpleasant surprise... wanna know what I am touching. Also, I have the service manual that ML sent me- I think I can deduce ins and outs.

I am driving with a quad 405. I do not listen at high levels and this will prolly be ok. I have an early early Crown DC300A - predates the sexy front panels and has zero ICs - all discrete components. I could use that if the 405 is underpowered.

Thank you for the help.

BIll

 

[JonFo]

Good to hear you have the schematic.

The transformer we are talking about is the big one, the audio signal step-up transformer, usually labeled as Tx1 in the ML schematics.
On the input, the voltage will be somewhere below 100v AC, so that's a good range to start. The output will be HV and in the 7.5Kv range. The Aerius uses a 70:1 Tx. I'm not sure what the clarity is at, but 75:1 is a safer bet. But be careful.

Hopefully, others who have checked the transformers can chime in with suggestions and cautions.

 

[wfissell]

Hi, I actually do not think I *do* have the schematic. I have one for the HV powersupply but thats all. If its availabel, please send a link!

Bill

 

[JonFo]

Ah, then yes, you need the schematic for the crossover element of the Clarity, contact ML, they should be able to send you that.

Also, FYI, another thread about clarity debugging: https://www.martinloganowners.com/threads/martin-logan-clarity-problems.17299/

 

[wfissell]

Hi, HV boards *appear* good but I do not have a way of testing 2500V (thats whats listed on the schematics) - anyone wiht suggesttiosn on how to test I am all eas.

thank you

 

[JonFo]

I've attached two documents describing how to check the HV voltages. I'm not sure who wrote them, but I had them in my stash of ML-related documents.

And related, you should check the voltage output from the small T1 transformer on the HV PCB, so this thread goes into that topic: https://www.martinloganowners.com/threads/aerius-low-output-possibly-hit-by-surge.19874/

 

[Jazzman53]

The diagnostics JonFo referenced above should nail down the problem but I will venture a guess that's consistent with the symptoms.

I think it's probable that both panels have lost volume due to degraded diaphragm coatings, and that may be the extent of the problem. However, when panels start going away the tendency is compensate the volume loss by progressively cranking up the amp power, which can ultimately smoke the transformers.

If the panels are weak but the transformers are OK, the sound will be bass-heavy, and the midrange will lack volume but should not sound distorted at normal amp power.

My guess is that your panels need replacing or refurbishing.

 

[wfissell]

My guess is that your panels need replacing or refurbishing.

I tested two new audio transformers from ML service and nothing.

The panels are not just quiet. they are silent. The digikey parcel with the 1 gohm resistors should arrive today.

thank you for the help.

 

[wfissell]

I used the 1 G Ohm resistor in line with the 1 M Ohm input impedance of the oscilloscope to do some probing. With the stat panels connected, theres about 850V DC at the HV lead on the power supply, with a fair amount of high frequency ripple on top - maybe 150V peak to peak.

With the stat panels disconnected the voltage is a bit higher, more like 2.2kV. At 1kV per division and 10microsec/div sweep, the left image is with stat panel and the right is without stat panel.

Thanks in advance for the help.