I have a couple of old HP power supplies that each have 4 large 20 watt ceramic wirewound resistors inside. these power supplies are probably 40 years old by now and while they still work fine. when powered on, within minutes the room is filled with that old funky nasty smell of hot dust/dirt/mildew/ old electronics smell. I have opened each one up and using a soft paint brush and a vacuum i have cleaned them the best I can but I need to wash down those resistors to try and de-funkify them. Does anyone know if you can by aerosol alcohol? or is there a safe to use spray type cleaning product that I could hose down the boards with?
De-Stinkifying Old electronics with Hot Resistors
- Thread starter Zero Cool
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Where in the circuit are they, what function do they perform? If your not looking to keep the power supplies all original for collector purposes or something, perhaps replacing them would be a better option. Digi-Key has many options that wouldn't cost too much. Chassis Mount Resistors | Resistors | DigiKey
Mike
Mike
I would shy away from the modern cleaners as many of them contain acetone and other chemicals that attack plastics. It would suck to have your polystyrene caps dissolve off the board in the cleaning process. I'd try distilled water first. If that doesn't take care of it, maybe some rubbing alcohol.
Tom
Tom
Besides tomchr's concerns regarding chemical content and possible leftover residue, most aerosols come at a higher cost too.
How about using a low cost air brush type setup, and then use the 99% isopropyl alcohol that can be purchased at any pharmacy counter?
Either that or just put the alcohol in a recycled spray bottle, and then use a soft bristle paint or tooth brush to work it in.
How about using a low cost air brush type setup, and then use the 99% isopropyl alcohol that can be purchased at any pharmacy counter?
Either that or just put the alcohol in a recycled spray bottle, and then use a soft bristle paint or tooth brush to work it in.
Replacing the parts is a last choice solution! I think I am going to try and rig up a stand to hold them upside down and then use a spray bottle with alcohol in it and a paint brush. The smell is so bad I am on the verge of an allergy attack from 20 minutes worth of use yesterday. I can try distilled water as well. maybe as a rinse?
I have had a lot of success in the past washing boards like pc tower or laptops with water myself.
First I remove any components that could be affected by liquids, fans, batteries, drives, cpu etc.
Strip it down to the practical bare minimum.
I use a few drops of dish soap such as Sunlight in a cup of water, then carefully work it around the board with a soft brush.
I then rinse the board off thoroughly with tap water.
To dry it I either place it in front of a floor fan for a half hour or so, or blow it off with compressed air (faster).
With compressed air you have to be very careful, do not get too close to the board or components and make sure that you dial down the pressure.
Even at low pressures if you are too close, you could end up blowing some components right off the board.
I have cleaned/revived at least 100 various boards this way, some with bad coffee, cappucino, expresso, pop and even soup spills on them.
First I remove any components that could be affected by liquids, fans, batteries, drives, cpu etc.
Strip it down to the practical bare minimum.
I use a few drops of dish soap such as Sunlight in a cup of water, then carefully work it around the board with a soft brush.
I then rinse the board off thoroughly with tap water.
To dry it I either place it in front of a floor fan for a half hour or so, or blow it off with compressed air (faster).
With compressed air you have to be very careful, do not get too close to the board or components and make sure that you dial down the pressure.
Even at low pressures if you are too close, you could end up blowing some components right off the board.
I have cleaned/revived at least 100 various boards this way, some with bad coffee, cappucino, expresso, pop and even soup spills on them.
Often for really old and dusty electronics, I like to use 409 cleaner (NO electricity connected) as it really removes grime like old cigarette smoke, dust, etc. Then I would rinse it with water, and air dry it. Isopropyl alcohol is OK too, IF it is commercial grade, and not from the pharmacy.
Marlboroughs or Camels?
If it is that resiny stink from mouldering 1960's tobaco product, TSP substitute and a little detergent + warm water and a soft scrub brush, rinse with clean water and leave out in the sun...
Orange Cleaner is another good surfactant. You can get it by the gallon at Home Depot. It's based on some oil extracted from orange peels. Great stuff. I use it as a general purpose cleaner around the house as well.
Whatever surfactant or detergent you use, an alcohol rinse followed by a water rinse should take care of any residues.
Tom
Whatever surfactant or detergent you use, an alcohol rinse followed by a water rinse should take care of any residues.
Tom
That funky smell can be phenolics and polychlorinated biphenyls.
What model/age HP power supplies ?.
Dan.
They are HP 6299A's I'm guessing from around 1966-1970 ish era. Old enough to say "Harrison" on them. One of which must have been stored in an attic or barn for many many years as it had a LOT of dust and dirt inside which I vacuumed out using a soft paint brush to break up the crude and get in and around small components.
Quite a machine and very useful power supply if not power hungry, but too good to dump.
The manual states First Rev Sept 1966 - http://cp.literature.agilent.com/litweb/pdf/06299-90001.pdf
I also see three 75W resistors, two 20W and 3W and 2W resistors, all potentially smelly.
You could remove these stinkers and wash them.
I would give them washes in a bucket with detergent, then bleach to remove all surface contaminants...don't forget to wash down through the ceramic tubes, push a piece of cloth back and forth, then hot water rinse thoroughly.
If you have an old benchtop toaster/oven, you could then dry/bake the resistors at high temp to drive off moisture and any smelly volatiles remaining.
This ought to help, but the rest of the machine may need cleaning also.
Can you post internal pics please.
Dan.
The manual states First Rev Sept 1966 - http://cp.literature.agilent.com/litweb/pdf/06299-90001.pdf
I also see three 75W resistors, two 20W and 3W and 2W resistors, all potentially smelly.
You could remove these stinkers and wash them.
I would give them washes in a bucket with detergent, then bleach to remove all surface contaminants...don't forget to wash down through the ceramic tubes, push a piece of cloth back and forth, then hot water rinse thoroughly.
If you have an old benchtop toaster/oven, you could then dry/bake the resistors at high temp to drive off moisture and any smelly volatiles remaining.
This ought to help, but the rest of the machine may need cleaning also.
Can you post internal pics please.
Dan.
Yes a pair of them configured for Master-Slave mode is perfect for solid state power amp front end design! 😉
Yes in the rear are 3x 75watt resistors but they are not hot. inside are 4x 20watt ceramics that get hot. one of which I don't understand it's purpose. It's a 2.2K resistor right across the bulk 150Vdc supply. it's just sitting there cooking off 10 watts of heat!
There is a 5K 20 watt that connects between the 125V supply and the 150V supply.
a 2.2K 20 watt that is connected to the base of the pass transistor and a 1.33ohm 20 watt as the sampling resistor. plus a handful of 5's and 3's
But I can feel the heat off the 20 watters and so I believe those are my stinkers!
Yes in the rear are 3x 75watt resistors but they are not hot. inside are 4x 20watt ceramics that get hot. one of which I don't understand it's purpose. It's a 2.2K resistor right across the bulk 150Vdc supply. it's just sitting there cooking off 10 watts of heat!
There is a 5K 20 watt that connects between the 125V supply and the 150V supply.
a 2.2K 20 watt that is connected to the base of the pass transistor and a 1.33ohm 20 watt as the sampling resistor. plus a handful of 5's and 3's
But I can feel the heat off the 20 watters and so I believe those are my stinkers!
Yes, those are the first I would try cleaning.
Worst case is you ditch them and replace with new ones....these machines are worth spending a few dollars on...maybe.
OTOH, a modern simpler supply could be built pretty cheaply.
A 1:1 power transformer, cap multipliers and a variac would do a suitable job for your amp front end development application.
Dan.
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