Quad ESL 988 strange issue - diyAudio
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Old 11th July 2014, 09:32 PM   #1
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Location: San Juan
Default Quad ESL 988 strange issue

The issue I have with one of my 988's is that it might be having a problem with the delay capacitor-coil board. This speaker has a lower output level than the other one. It has no strange noises nor sparks and it seems all the panels are working.

The previous owner used to ship the speaker panels for service without the electronics attached so to economize in shipping cost. Upon inspecting the electronics I noticed the cap boards were dislodged from one of the coil boards, so it was probably mangled via shipment. I have been trying to fix this by reconnecting the solder joints. Yesterday, I noticed that there were 2 additional connections that were dislodged -more like cold joints- , fixed them and it got better but still output is lower. I believe that there must be something going wrong with the coil cap board which I have not been able to find. It seems it has to do with voices.

Has anyone had a similar problem? Maybe one of the coil leads in the printed circuit got damaged or cut and there is no continuity in the coil.

I have seen complete cap-coil boards for sale in the internet I wonder if this might help.

Thanks in advance.
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Old 12th July 2014, 11:08 AM   #2
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Hi,

It could be a lot of things but I'd first check out the high voltage if it is up to spec. Or exchange the high voltage supplies between speakers to see if the problem moves along with it.

Were all 8 panels serviced or only the panels from one speaker? I have seen a lot of panels from a certain manufacturer(s) that loose sensitivity over time. Panels go down in output over the years between 5 to 15 dB or even stop working completely.

Those are the two most likely candidates IMO. Swapping parts between speakers would be a good idea to find the culprit.
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Old 16th July 2014, 08:35 PM   #3
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Got it fixed. Cold solder joints that were fixed. Thanks.
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Old 26th July 2014, 05:05 PM   #4
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Default Not really! Interesting discovery.

Jumped the gun. The problem persists. What I did was to breadboard a second volume control , so i now have a volume control for each channel.

I can dial now a balanced image without any frequency response issues. Doesn't this rule out any panel anomalies a point to an eht board issue.

Thanks for reading.
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Old 29th July 2014, 01:02 AM   #5
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Default Update

Swapped the mother boards and the problem persists in the same speaker, so it is not a problem with the eht circuit.

Thank for reading.
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Old 29th July 2014, 03:04 PM   #6
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Have a look at the Neon charge indicator lamp. It should be flashing at around 5 times per second. Compare it with the good speaker. This would tell you if the panel has a leakage path (neon is on solid or flashing very fast).
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Old 29th July 2014, 04:47 PM   #7
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Quote:
Originally Posted by Mike Beck View Post
Have a look at the Neon charge indicator lamp. It should be flashing at around 5 times per second. Compare it with the good speaker. This would tell you if the panel has a leakage path (neon is on solid or flashing very fast).

NO!!! the "charge indicator light" fires whan the differential between the HV supply and the net voltage charge on the panels reaches 70 volts or so. With good panels in a dry environment, the light may "only" fire once every 20to thirty seconds or do. In a "dry" situation, if the light fires continuosly, then you have a bad panel (or two). The panels don't have to be "arcing" to break down. Look at them carefully in a dark room and you my see a "glow" or glows here or there in suspect panels where charge is accumulating and "escaping/leaking".

If the indicator fires continuously, (a) bad panel(s) could be lowering the high voltage which could reduce the net volume. A distorted signal typically means that the protection circuit that fires the Triac across the transformer primary may be activating (correctly or not). Or there could be some problem with the voltage clipper circuit on the transformer secondary.

Charles
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Old 31st August 2014, 06:50 PM   #8
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Hi Manolo47,

I assume the ESL 988, is like the ESL63 which has a small neon ligh hidden under a rubber button. I quiet agree with Mike and Charles you should check the "indicator" light flash rate, and tell us all.

I think both of them are a little off, on the flash frequancy but Charles great numbers is closer to the ideal than Mikes timings which I think are a sign of his ESL speakers failing.

Quote:
Originally Posted by stellavox View Post
the light may "only" fire once every 20to thirty seconds or do. In a "dry" situation,
20 to 30 seconds is exceptionally low leakage. I observed my ESL63's flash every 12 - 4 seconds depending on the weather in rainy Hamburg. Ideally they would never flash, but high voltages do leak.

If the 988 does not have in indicator light you could add one to the ESL bias supply.
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Old 1st September 2014, 01:38 PM   #9
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Default Indicator light and other findings

The 988 has the indicator light inside the electronics enclosure and it blinks ver fast, like it never really goes off.

So, that would mean there is a leak. But, i have checked the speaker in question
Operating without any lights on and without the sock and could not see any sparks or glow.

One thing i noticed yesterday is that this low output was intermittent, that is, for about 2 hours yesterday both speakers had the same output.... Someone might make something out of this. Also the difference in outputs is 4db. I mitigate this by installing a Dact attenuator in the "good" channel preamplifier input and lowering the input signal by only 2 clicks, which I believe would be 4db. Everything falls into place. The affected speakers appears to have full frequency response and does not emit strange noises. I understand there is a leak somewhere and shortly plan to dismantle the speaker to check al the panels, stator glues and diaphragms and electrical connections. I will start with the middle 2 panels though it seems that these might be the culprit though one stars to notice the misbalance once voices are up. Again, someone might make out something out of this. Thanks.
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Old 1st September 2014, 08:15 PM   #10
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Quote:
Originally Posted by Manolo47 View Post
So, that would mean there is a leak. But, i have checked the speaker in question
Operating without any lights on and without the sock and could not see any sparks or glow.
According to the service manual for the ESL63 (you shodul get this as the speaker pannels are the same) If you try leaving it runnign for 24 hours it will probably get worse and you will be able to see the sparks or glow.
Quote:
Originally Posted by Manolo47 View Post
One thing i noticed yesterday is that this low output was intermittent, that is, for about 2 hours yesterday both speakers had the same output....
This suprises me, and makes me wonder if its dirt / dust inside it? Maybe you shodul inspect the dust cover for holes. When you do consider stripping it down do avoid a dusty enviroment.

Good luck, it is most likely a damaged pannel, fittign a new diaphram may well resolve the issue.
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