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MC 1502 Miss Snow White

AudioWizard

AudioWizard

AK Subscriber
Subscriber
Customer brought in this MC1502 in yesterday with a blown fuse thinking it had a bad power tube. Noticed that it had a white film all over the tubes and chassis. Questioned the customer about that, he said he has an humidifier in his house. Decided to remove the bottom panel to check it out. Board covered in this white power, all the Wima's are white! Checked all the power tubes (KT88) all good, no shorts, some weak. Took it out back and blew it out, still has a white film, but much better. Installed new KT 88's as per customers request. It runs, but who knows about the other side of the board? So a total disassembly required , so I can do a cleaning of the main board both sides. Check out the pic of the diodes, a band of white powder, weird ! So a question, is this powder conductive?
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It's most likely mineral residue from the water and humidifier he's using. Ultrasonic and impeller humidifiers are known to do this. The residue is most likely made up of calcium and magnesium, is not conductive, and is unfortunately attracted to electronics. That stuff is probably everywhere in the room or rooms that he's using the humidifier.
 
Hello AudioWisard

I never seen that before in any MCINTOSH I got for repair during these last 45 years
I think that cleaning everything everywhere will cost a lot in time and money , and this will come back again after some months !


No trace of white powder on all pcb except on the power audio board + power pcb and choke !

There is a choice to decide
audio system (MCINTOSH or any other brand) in house or humidifier
 
It seems to be mostly where the high voltage is. I have never seen this before either in 47 years! I can only imagine what the inside of the customer house is like or his C2700 preamp. Basically I have to remove everything accept the transformers to properly clean, the clock will start next week. Good news he is getting rid of the humidifier !!!
 
@jayvis is spot-on, minerals from a non-evaporative humidifier’s supply water, a heavier-than-air dust that tends to cover everything, but dust is attracted to high-voltage, a tube-amplifier will have the highest voltage in the room (unless the owner also has a CRT TV or computer monitor!).

I’m thinking it’s probably non-conductive but, ... there is usually some salt in that water also, ... and with humidity it can be both corrosive and conductive. I’d probably give the whole thing a nice alcohol spraying to see if it can all be washed off.
 
I'd be tempted to button that ol' girl back up and hand it back to the customer. Otherwise, you're married to it . . .
 
What would McIntosh do if that amp were sent there? That would likely be your best course of action, and that's not going to be inexpensive.

The world needs more determined folks like yourself. I wish you the very best of luck with it.
 
I could always order a complete board if I had to, I just did this just recently on a MC-611 that a cat got sick on. Was lucky that the board was in stock and not have to wait for the next production run. That's what is nice on current models parts are available.
 
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