Monster Pro 2500 High Pitched Whistle

[Danlampton]

I have this unit on the bench and it whistles when it is pluged in - switch can be on or off.

There is a half inch round component on the circuit board that is making this sound. It is labeled BZ101 but I do not have a schematic.

The front outlets are fine but none of the back outlets work.

Any ideas on what the component is and why it is whistling at me?

Thanks.

[Mark Black]

Well, I sort of doubt Monster will turn loose of a schematic but you should probably give it a try.

If I had to take a wild guess I'm thinking they may have incorporated a switching power supply to run the logic/relay circuits and that has developed a problem. Whistling sounds are one symptom a SMPS can exhibit when they are sick.

Any chance of some pictures of the board & suspect component?

[Danlampton]

Thanks for the response Mark. The black round circle in the middle is what I'm trying to identify.

Thanks.

[Mark Black]

Well, I don't see anything that really resembles a SMPS power supply. I was trying to figure out what that component is and it dawned on me - I think it's a buzzer (hence the BZ designation). And indeed it does look like some piezo signaling devices I have seen (check this out): PS1420P02CT TDK Audio Indicators & Alerts

Nothing revealed in the owner manual about any kind of buzzer or audible signaling (just a lot of Monster hype & VERY sparse instruction), so what its purpose might be is a mystery. I would think it is probably not the cause of your problem but rather a symptom...

Edit: I looked around and did find reference to "audible & visual alarm to indicate a surge has occurred" in the descriptions on some reseller sites, so now I REALLY think it's a buzzer/siren/alert kind of thingy.

[Danlampton]

Thanks for the detective work Mark. This helps so much.

[Enzo]

My reaction immediately to BZ101 was Buzzer. And I have to say I have never seen or heard of an amp that made noise to tell you it had a problem, at least not on purpose.

I se a large relay, so I bet the speakers remain disconnected from the circuit. Can you determine if there is DC on the amp output on the amp side of the relay?

[Steve Conner]

This is not an amp, it's a power conditioner.
PRO 2500 Rack Mountable PowerCenter™ with Clean Power™ Stage 2

The kind of thing that only exists so the managers at Monster Cable can eat.

Maybe the buzzer is telling you that the MOVs have eaten one surge too many, failed short, and need replacing.

[Enzo]

Oh. Well that is very different, isn;t it. Never mind...

[Mark Black]

For some reason this thing has piqued my interest...

So I did find something in the FAQ section of their website: "Audible alarm sounds when the protection circuit has been disabled. The product should be immediately unplugged. Contact your dealer or Monster Cable for service."

It may well be a leaky MOV as Steve suggested, or there may be a picofuse on the board that has opened up. Or there may be a secret reset procedure that would be revealed when you contact Monster.

In any case I think it's silly that there is no mention of the audible alarm in the operator manual - apparently Monster products are designed to be used only by people with internet service and inquisitive nature.

It will be interesting to see how long this thread lives before Monster files a DMCA for using their name. I can't think of any other equipment manufacturer website where there is a contact link "For Legal or Intellectual Property Matters" in the support section...

[Mark Black]

Danlampton I don't know if you are still following this thread, but I have new information and thought I would throw it out here in case it helps someone.

In one of those funny/strange quirks of electronic repair fate a guy brought in two Monster Pro3500 units today (I have not previously worked on any MonsterPower units and didn't even know they existed until your post). Curiosity got the better of me and I had to have a look inside at least one of them to see if it was similar to your Pro2500. I'm guessing after looking inside there are a lot of similarities.

That one had the exact symptoms you describe for your unit, with the high-pitched sound coming out of the buzzer and no output from the rear outlets. I found the cause to be an open (and somewhat hidden) thermal fuse joined to a MOV under heat-shrink near where the power comes into the PCB.

Now here's the thing: that fuse (NEC SEFUSE SF96E) is rated at 99 degrees C and/or 10 amps. AND IT FEEDS ALL OF THE REAR-PANEL OUTLETS!! They obviously designed things so if that MOV got hot (presumably from repetitive spikes or dangerous overvoltage) it would open the fuse and protect the gear plugged into the rear-panel outlets, but the fuse also becomes a choke-point for power availability due to the 10A rating. I'll bet the turn-on inrush current of one Mackie 1400i or Crown Macro-Tech 2400 would be enough to blow the fuse. Certainly the accidental plugging-in of a couple dimmer packs with stage lighting attached (as was the case with the unit I was working on) would do the trick nicely...

Additionally the two circuits labeled "Digital" and "Analog" (which have the most filtering) are switched through relays rated at only 5 amps, so don't be plugging any power amps into those outlets! The "High Current" outlets are run through a 30A relay, but are still downstream of that 10A fuse.

In a nutshell the total output from any combination of all the rear-panel outlets is limited to an absolute maximum of 10 amps, which equates to about 1200 watts (at least here in the USA with 120VAC power).

That's more stuff which seems like it should be stated in the owner manual, but of course it's not mentioned at all.

The only seller of small quantities for that exact thermal fuse I could find is on Ebay and located in Hong Kong. I found a 100C 15A version (NTE brand) sold through Mouser, but am not so sure of the advisability of jacking up the current availability due partly to the 5A relays. Heck - I'm not out to re-engineer this thing, just fix it. I'm sure I'll come up with something close enough in a few days from one of my less-usual suppliers.

Just thought I would share...

[Danlampton]

Thanks Mark. That is unbelievably helpful. I hadn't found that fuse - really didn't want to cut into the heat shrink until I knew what I would find.

[Danlampton]

Mark, I've found a few at 98C and 100C - both 10A.

THERMAL FUSE 98C 10A AXIAL - SDJ1 DF098S

I would think 98C would be fine. What do you think?

[Gibsonman63]

Same thing happend to me on a Monster power strip. They have a lifetime warranty. Just call for an RA number and they will send you a new one. I also had a clod-footed drummer step on two Monster instrument cables and break the ends off... the same night. GC exchanged them with no questions.

One of the few advantages of overpaying.

[Mark Black]

Hey Dan -

I would think either 98C or 100C would work just fine. The vagaries of simply slapping that fuse up against the MOV with no thermal grease and no particular attention to contact surface area probably far outweighs any few degree difference in rating.

Thanks for the link. Now if I can just think of a few more things I might need from Digi-Key to amortize the shipping cost...

[Steve Conner]

Don't forget to replace the MOV too. The fuse is thermal because MOVs have a known failure mode, they go leaky and catch fire.