Monster Pro 2500 High Pitched Whistle

[Mark Black]

Good point Steve.

The units I'm working on had a known over-current event (lighting plugged in) and the MOV's seem to be fine, but I would be pretty suspicious of the MOV's if I didn't know the history.

On the other hand the MOV's they chose (and there are quite a few in addition to the one next to the fuse) are all rated at a 750V trip so I wouldn't think they often get much of a workout. That's another thing I find a little odd...

[ziggyb]

Dan, or Mark or Steve: Were you ever able to repair the Monster Power PRO 2500 by replacing the thermal fuse and the damaged MOV components as specified by the helpful expertise of the gentlemen in this thread?
I had the exact same thing happen to mine last night at a very important gig and it was awful. Died in the middle of a song....
I am going to try to call Monster, but I am curious to know if this repair is feasible.
Hope you helpful dudes are still out there!
Thanks very much....Ziggy

[Mark Black]

Hi ziggyb -

I was able to repair both of the units I was working on by simply replacing the thermal fuses (I used the ones from Digi-Key that danlampton pointed out). Of course when I say "simply" I should add that it takes quite a bit of physical disassembly to access the solder side of the PCB...

Good luck with yours - I hope it is equally as simple.

[ziggyb]

excellent news!

Mark,
Excellent! I ordered the very same thermal resistor from Digi-Key for .98¢ today.
I have already disassembled the unit and have the PCB out on my workbench. I could not satisfactorily match up the MOVs, so I gave up on ordering those. From what I gleaned from your msgs, it sounds like the MOVs should be ok, however. The unit has 16 of them, and the best match I could find was they might be made by Vishay/BC. But the existing ones in the Monster only say "TVR 2075", and I could not match them up on the DigiKey site. They measure 20mm in diameter, and I only see 17 and 23 mm on the site. I don't know enough about the subject of Varistors to make an effective judgment call. I do not know how to test them to see if they are good. But as far as dropping in a simple replacement component, that I can do. I am a working bass player and a hobbyist, so my tech knowledge is modest when it comes to electronics. But I SURE DO appreciate your INVALUABLE help, as I was looking at buying a whole new unit with money I don't have! Sincerest thanks, and I am hoping for the best...

[Danlampton]

The thermal fuse took care of mine. You might need to replace the buzzer as well - or just leave it out of the circuit.

I burned up one fuse soldering it in place so be careful. For my second attempt I clipped some heat sinks on the leads above the board - I used alligator clips.

Your MOVs should be fine.

[ziggyb]

Monster Pro 2500 repair is in full swing

Dan,
Thanks for writing...
I tested my unit this morning by plugging it in and verifying that the front outlets work. The buzzer is happily squealing away (you can quiet it down by putting your finger over the hole on the top of it.) so I think it's ok. I stupidly overloaded the unit at our gig Saturday and that is what blew the TR.

I would like to know an answer to a question my drummer asked me: "Why doesn't it simply have a larger breaker on the front, or a second breaker that will trip if the load goes to a certain threshold? Why go to the trouble of installing a Thermal Resistor on the PCB which requires all this labor to fix?"

I guess the simple answer that occurs to me is twofold: #1) You're supposed to not be a dumbass (like me) and not overload the stupid thing in the first place! And #2) The TR is the best solution to prevent destroying the unit and all your precious soundgear because of your failing to heed #1)....
Does that sound like a fair assessment?
I know I will be a LOT MORE CAREFUL in the future and PAY MORE ATTENTION to the specs!
(;

[Danlampton]

Can't say why the circuit was made this way. I'm sure it is much cheaper a sensor and a driver and a breaker. Remember this particular issue isn't about the load but the heat (of course one can lead to another). I didn't order a new buzzer when I ordered the fuses and my customer didn't want to wait, but you will need to replace it or remove it or put up with that racket.

[ziggyb]

Are you saying the buzzer doesn't reset itself once it's tripped on? Is a reset possible with such a device? Hmmmm, that's interesting. If so, then yes, one possible solution is to disconnect it...Thanks for the tip!

[Danlampton]

The only one I worked didn't reset. That's all I can say.

[Mark Black]

A quick test to see if the thermal fuse replacement will shut up the buzzer is to simply clip a test lead across the old one. That's how I tested the units I worked on before ordering parts and as soon as I shorted across the fuse the buzzer went quiet. That was done initially with no load plugged in, and then operation verified with a 60w light bulb plugged in to each of the outlets.

In retrospect I think the units are a joke due to the 1200W overall load limitation and use of 5A relays on two of the sections. The only cool thing about them is the front-panel voltage/amperage display and the fact they sequence the power-up of the rear outlets, and in reality the sequencing could/should be done manually by turning the gear on/off in proper order.

Equivalent Furman units are MUCH better designed & built.

[ziggyb]

aargggh, it doesn't work....

I replaced the thermal fuse exactly as specified with the new one from Digi-Key, carefully put it back together and the darn thing doesn't work. The buzzer is still squealing away and the back outlets are not operational. Neither do the front panel lights under the voltage LED. There is an audible "click" from a relay when you turn it on, but nothing else. Front 2 outlets work fine.

Can anyone help? Does the buzzer need to be disconnected from the circuit in order for it to resume function? Or have I fried additional components that I am not aware of?

A little stuck after ordering a new thermal fuse. Appreciate any help!

[Danlampton]

Have you checked the fuse for continuity after soldering it in place? Like I said, I tripped my first one by the heat from soldering it.

[ziggyb]

Sending it back

Thanks for your input. I think that may be exactly what happened. I had my solder gun set for 600F. I wonder if I shouldn't have used a lower temp?....However, it seemed to take forever for the solder to melt, so yeah, that may have been it, and I only ordered one fuse...But in my defense, I did have no less than 3 small heat sinks connected to it! It is a thermal fuse after all, and it does respond to heat!

After some deliberation as to what to do next, I called up Monster (expecting the worst) and after waiting about 20 mins on hold, lo and behold, I was able to get an RMA # with instructions on how to ship it back. ( Mine is still on warranty, which is 5 years, BTW) Didn't ask if I opened it up. They ask you if it's squealing, and they ask you if it damaged any of your gear? I said no, and the nice girl said "Well, It did it's job then!" So, apparently these things are designed to die and protect your equipment if you get a massive surge. I could not argue that logic. (Mine got a pretty big spike.)

So, I am shipping it out today. Will take 3 weeks or so, hopefully I will get a new unit. I am hoping no one opens it up and checks for a replaced fuse and I left the heat shrink off since I chopped it up. I have a feeling they must get hundreds of these things in some big warehouse. I bet all they do is plug it in and if it squeals, it's replaced. Hope I'm right....
Thanks again for your prompt assistance!

[DIY_Guy]

Hey I hate to hijack this thread, but quick question. Can anyone tell me what the value of the Zener at ZD101 is? I have one here that has this Zener fried to a crisp and can't determine the value of it. Thanks!

[Mark Black]

Sorry from me - units long gone...