High-voltage boards?

[EricE]

Has anybody experienced a problem with their high-voltage boards on their speakers? Specifically I have Quest Z's and the left channel is experiencing a sort of static/clipping sound. I have swapped speaker connection and cleaned them and it still seams to be the left speaker.

Mind you it is only during loud playback passages. During low to mid sound levels the speakers sound fine....????

I've been in contact with Jim at ML and it looks to be that item but I just want to hear other peoples experiences.

 

[Statman]

I had to change one of my boards in my Odysseys when I noticed the one channel starting to not play as loud as the other. Jim Powers helped me out a bunch walking me through the process. The only thing I realized when taking the speaker apart(removing both woofers and the board is that it does look rather "cheap looking" for what you pay for them, mianly the woofers and their magnets and the actual frames of the woofers! Works fine now!

 

[Jeff Zaret]

I had the power regulator board g outin my Sequell II's. I just lost all power to the panel on one side and it kept blowing fuses. The woofer did play a bit. I replaced both boards and everything was fine. I was not hard to do in the Sequels and I think the QuestZ's may be similar but I have been wrong before.

Good Luck

Jeff

 

[EricE]

Thanks for the replies gents,

I took out the rear panel last night and everything looked fine. I was looking for some frayed wires or some evidence of some hi voltage arching but I could not see anything to my eye. I may just replace the board and hope it fixes everything.

 

[risabet]

The boards are certainly lovely but you can't tell by looking! Go ahead and replace them. They're still under warranty I assume?

 

[Statman]

As risabet said you can't see the problem, it's usually one capacitor(usually) that's out of value that causes the board to act up at least that's what happened to mine.

 

[Peter Hogan]

Thanks for the replies gents,

I took out the rear panel last night and everything looked fine. I was looking for some frayed wires or some evidence of some hi voltage arching but I could not see anything to my eye. I may just replace the board and hope it fixes everything.

Hi,
Looking at the pics, I see in the first one the large blue capacitor has its blue heat shrink covering split in several places. This is not normal, and would indicate that it has been overheated at some point. I would check this component VERY closely. It may be the culprit, especially if it is breaking down internally at higher voltages (i.e. loud volumes).
This PCB is the crossover/equalization board, the one with all the orange capacitors is the high voltage bias board.

HTH,
Peter

 

[EricE]

Thanks for the informative info gents. Jim at ML also suggested to replace the caps and see if it solves the problem.
Thanks for the heads up peter. I thought that upper board was the high voltage board but the main 120vac power is on the bottom board... The large transformer and choke on the upper board does make sense to be the crossover.

Another strange thing that I don't understand is that I can play the Quest Z unplugged for the 120v mains and it still sounds OK. I thought the sound would die from the stators without the power plugged in. I did not try this on the other speaker though...

 

[DavidG]

Thanks for the informative info gets. Jim at ML also suggested to replace the caps and see if it solves the problem.
Thanks for the heads up peter. I thought that upper board was the high voltage board but the main 120vac power is on the bottom board... The large transformer and choke on the upper board does make sense to be the crossover.

Another strange thing that I don't understand is that I can play the Quest Z unplugged for the 120v mains and it still sounds OK. I thought the sound would die from the stators without the power plugged in. I did not try this on the other speaker though...

You'll find that the panel will hold some charge for a while after the power is taken off, hence they will play for a while. It's also why you're recommended to leave them powered down for several hours before vacuuming the panels.

Cheers,

David

 

[EricE]

Anybody know where I can get 470uf 100vdc caps online? I'm also looking for the 15uf cap but is it the same 100vdc rating?

 

[Peter Hogan]

Anybody know where I can get 470uf 100vdc caps online? I'm also looking for the 15uf cap but is it the same 100vdc rating?

Hi,
You can try here for the 470uF@100Volt cap:

http://www.digikey.com and enter 4262PHBK-ND for the search parameter.

and here for the 15uF@100Volt one:

http://www.digikey.com and enter 4089PHCT-ND for the search parameter.

HTH,
Peter

 

[EricE]

Thank you very much Peter.

I've placed an order today and I hope it all works well.

 

[roberto]

measure the high value resistors...

Thank you very much Peter.

I've placed an order today and I hope it all works well.

Hola EricE. Also check the resistors, some are 15 M. or higher. From the red color of the stat panel cable connector of the printed circuit board, there are about 5 resistors connected in series (brown, green, blue, silver or gold tolerance)...at the end of the voltage multiplier. I have had here in Costa Rica, and several times, an open resistors, so the panels fails to work as they should. I have never changed a capacitor. Only bad resistors. I have represent ML over 18 years here and of course I have to provide service to them some time once in a while. Hope this can help!!

Happy listening,
Roberto.

 

[EricE]

Hi roberto,

Are you talking about the resistors on the high voltage board?

 

[Peter Hogan]

Hi roberto,

Are you talking about the resistors on the high voltage board?

Hi,
They are on the high voltage board, but not the ones you have circled (those are part of the circuit that turns on/off the high voltage when music is present). The ones he mentions are at the end of the orange caps, at the left end of the board in the picture.
The small transformer on the board steps up the 120 VAC to about 500VAC, then each pair of orange caps and diodes rectifies and multiplies that, so you get about 500 volts added each step of the way. You have 6 pairs of caps, so your high voltage will be around 3000 volts. Then it goes through the 2 high value resistors on the left end of the board, and on to the panel.

HTH,
Peter

 

[EricE]

Thanks again Peter and Roberto.

I got the replacement caps from DigiKey the other day and replaced them. I had a quick listen for a while and it seemed to clear up the static/clipping sound. Later on I went to watch a movie again (specifically the LOTR ROTK) and durring the main battle scene the speakers passed the sound on greatly for a while but eventually it started again...

I may have to order a replacement high-voltage board afterall.

 

[EricE]

As an update, I found replacement caps and I installed them but the problem still persists... I've done a few more tests and I did find some issues that my give you a clue as to the source of my problems with the Quest Z.

I moved my Aerius i's for the rear channel to the fronts to see if there was a problem with the protection circuitry on my amp. To my surprise the Aerius' played very loudly and with greater high frequency extension. When I calibrate my HT system I usually find that I have to boost the output of the Quests by about 9db just to equal the output of the Theatre center channel and Aerius surrounds. I always thought it was the design of the Quests.... When I substituted the Aerius' and recalibrated the system, the Theatre center and Aerius' we almost at the same levels.

I'm thinking now that the Quest Z's have a problem with the HV boards and that the low output and recessed high frequencies are the symptoms of weak HV boards or transformers.

What are your thoughts on the HV boards?

 

[EricE]

I spent about 5hours yesterday fooling around with the speakers and equipment at home. Accidentally I was touching some cables behind the amp and a huge noise came through the front speakers (hummmmmm) It looks like there is a bad shield connection in one or both of the RCA interconnects. I found this out around 11:00pm.

I think I solved the problem! Can't wait to get home to reterminate the ends. All this time I was blaming the speakers for the problem. Then I thought it was the RCA inputs on the amp since the Balanced connections sounded OK.

As a side note I also swapped the Quest Z's to the rear and the Aerius i's to the front. I was listening to both the Z's and the I's strictly as surround with the other speakers disabled and WOW! The amount of bass and overall sound from the rear channels was amazing even with the processor set to small speakers in the rear with a 80hz cutoff. Now I'm thinking of selling the Aerius i's and keeping the Quest z's for rear channel duty and getting Ascent i's for the front.

 

[m2bozz]

Hello,

Does anyone know where I could purchase a high voltage board with all of the components?

Thanks
Mike

 

[Jeff Zaret]

The only place I know is from ML. I had a bad power board in my Sequel II's and they replaced it with no problem.
I would reccommend replacing both since they are the same age and you know the other one may die soon. I think both of mine were about $178.00 USD?? It came with instructions and was easy to change.

Give Jim Power a call at ML. Just dial there phone number, (785)749.0133 and ask to speak to him. He is a great guy and extremely helpful.


Jeff