[wreutz]

Hi all,

maybe someone can give me a hints what's wrong with my MP566:

I built it some years ago, since then using it for live sound for my main vocal channel as the first stage followed by an EQ573 and CP5176.
Working like a charm and never let me down!

Three days ago it suddenly stopped working. Input led went dark and no switch changing or on off of the lunchbox fixed the problem. I removed it from the lunchbox as it was in bright sunlight and got a bit hot but not tooo hot! After some hours I reinstalled it and it worked. Day after that it worked and today I'm testing things at home and after initially working it suddenly stopped.

I changed the tube to an older one and it seemed to be the fix at first but after about half an hour it again stopped working.
Then I noticed that it emitted a strange sound like a square wave or low frequency digital noise (just lows and mids, no highs as a sound description).

Swapped the tubes again and now it's working for the moment.

My question now is:
is this a sign of a dying tube or is there something else broken? No obvious signs visible like blown up parts or goo or nasty stuff ...

Any help greatly appreciated 😉 

[JPK]

I don't think it is the tube. More probably the high voltage converter U5 or a resettable fuse PTC1 or PTC2.
The high voltage converter doesn't like being very hot.
When it happens again check the high voltage (+225VDC) on TP2 as well as the heater voltage (-4VDC) on TP8, against 0V.

[wreutz]

Thanks for your help!
Had no time over the weekend to work on this and now I got my replacement tube. As you guessed, it didn't fix the problem. After about half an hour the problem returned - then after turning off the lunchbox for about 5 minutes got it working again and it started like the sound was faded in.
So maybe your guess with the high voltage regulator is correct.
I will investigate that further and will order the replacement parts anyway as it's a good idea to have spare parts around 😉 

[wreutz]

Ok, now I got the replacement part for the high voltage converter and replaced it. After continuous run for over an hour I guess it's considered a fix. 😉 

Bought it almost exactly 8 years ago, just one broken part is a good outcome!
I really like the Sound Sculptor kits for it's quality and sound 😉 
and the good help on this forum

[JPK]

Just make sure it doesn't get too hot 👍

[wreutz]

Sorry to bother you again.

I used it this weekend at a festival and I worked like a charm. about 45 min prior to the gig and the 1 hour and one of the main vocals was using the MP566 in the insert. So far so good 😉
After the hour the gave an encore and just in that moment the main vocalist was gone on the PA and no input signal on the MP566.

So two questions:
- I know, don't let it get too hot. BUT it worked in that API 500 casing for the last 8 years! and in the rack I have one rack unit with a mesh for ventilation above the API rack.
- second: I didn't change the resettable fused yet. As you mentioned, I want to try that next.

While removing the PTCs from the board I noticed that the ones used in my revision of the board are 200mA and in the newer documentation 300mA resettable fuses are used 😳 
Could this be a cause for the problem as well (obviously the high voltage converter was worn out too over the years as it worked way longer than with the old device installed)?

Is it save or even a good idea to use 300 mA PTC instead of 200 mA for revision 1.3? (last modified 07/07/2015)

[JPK]

Yes you should upgrade the PTC's to 300mA ones.
In the mean time you could short them with wires. The PTC's are there to prevent shutting down the whole lunchbox in case of a module failure.

[wreutz]

Thank you!

I guess that fixed my problem.
Both the DC converter and the two PTCs had to be replaced and the upgrade from 200mA to 300mA finally fixed it!
Thanks for your fast and continuous support!

Tested the preamp for 2 ½ hours and had yesterday a gig and no problem at all!

Really love your modules!

[JPK]

Great news!