Immersing in alcohol


70% isopropyl, actually. And I'm talking about my 9810 printer, which I started trying to clean today.

What a mess! Massive quantities of tarry black goop that obscure some components so much that I can't even see what's under it.

Is there any reason I couldn't let large portions of the printer mechansim (circuit boards, printhead, mechanical bits at the front, not the motor of course!) simply soak in a tub of isopropyl for a few hours?

UPDATE: It seems this is a common method of cleaning electronics, but with 90+% iso rather than 70%.

Edited: 28 Aug 2011, 4:35 p.m.


I can't think of anything in the (other types of) hp printers i have had apart that alcohol would destroy but the already-destroyed rubber rollers. I wonder where that much goop came from.

Re:soaking. I use the "little bit for the printer, little bit for the printer rebuilder" method.


The 70%, with more water, will be slower to evaporate. The other risk is that some part may retain water.

What about the Carbon Tet replacement? Trichloroethylene, I think. Risk to plastics?


Most good drug stores (not most of the chain ones) sell 99% isopropyl alcohol.


Is it generally agreed that 99% is the best to use on restoration projects due to the low risk of leaving water behind?


So far, I've gone through a quart of 91% just cleaning the printhead and its associated ribbon cable and PCB. Yuck.


Hm. 1.5 quarts of 91% alcohol later, and the 9810 printhead/flex cable/PCB has graduated from "buried in goop" to "very dingy". Most of the remaining goop is cosmetic, but some isn't: for example, the minute traces in between the printhead resistors.

I don't think it would be a good idea to heat that goop up!

I think I've reached the limit of what I can do with alcohol and a toothbrush. Any suggestions on where to go from here? I have some acetone, but I know it can dissolve plastics (it's good for hand cleaning after getting the goop all over them, though...)


Err, yes. That gunge is really nasty, and gets everywhere. I've even had it inside the edge connector between the keyboard cable and the backplane (located unfer the printer) where it can cause bad conenctions.

The only way I've found to get rid of it is to completely dismantle the printer. Some parts are not likely to be affected by any common solvent (e.g. the side plates, metal spindles, etc), others might be (like the plastic gears). I remember trying all sorts of things on my printer, but I think propan-2-ol (ispropyl
alcohol, isopropanol) was what I used most of the time. And yes, I used a lot of it. Propan-2-ol will not attack any part of the printer AFAIK.

Acetone/Propanone will not damage any of the metal parts. I am pretty sure the plastic bearings in the front section are PTFE and will not be attacked by acetone either. Try it carefully on the flexible PCB (I am pretty sure it's OK) and on the printhead.

I can see no good reason not to leave most of the bits sitting in a bath of solvent. It's not going to damage them. But I wouldn't leave the printhead or PCBs soaking in acetone, just in case.

You probably want to separate the printhead from the driver PCB 'tail'. Loosen the allen setscrews in the clamp and it'll all come apart. Realigning it when you put it back is not that hard. Take great care when cleaning the head (you can crack it!) and the flexible PCB tail.

There's probably no need to dismantle the motor (the gunge rarely gets that far back!), but it is possible. From memory, you take off the rear cap (3 screws) and the plastic sleeves under it. Then take off the drive pinion and spacer, the circlip and washers from the spindle, and slide the rotor out. Handle that with care, it's brittle!. Then unlock the rear plate on the stator by rotating it, take that out, the large spring washer, and then take out the stator parts one after another. Mark the coils so you get them back in the same order and the same way up (otherwise it may run backwards when you reassemble it).


You probably want to separate the printhead from the driver PCB 'tail'. Loosen the allen setscrews in the clamp and it'll all come apart. Realigning it when you put it back is not that hard. Take great care when cleaning the head (you can crack it!) and the flexible PCB tail.

I had hoped to avoid this since I worry about getting the alignment right when reassembling it. But the gunk is way down in the crevices, and I suppose I should if only for completeness.


There are 3 things you have to get right when you refit the printhead :

1) The traces on the end of the flexible PCB tail line up with the pads on the printhead

2) The printhead is 'level', not sloping too much to one side or the other relative to the clamp and the PCB tail

3) The printhead is about the right distance above the clamp (this can be compensated for by the adjustment cams, but they have a limited range).

It's a bit of a fiddle to get right, expect to have to slacken off the clamp and refit it a couple of times. I am sure they had some kind of jig to hold it at the factory, but I've never needed to make one.


Again I refer you to Trichloroethylene. Carbon tetrachloride was "the" non-destructive degreasing solvent of choice before it was phased out. Trichloroethylene is its replacement. As always, you should test on some hidden area of plastic before wholesale use.


At work there is an old HP35 lying around. It was used by one of our Surveyors back in the 1970s. Unfortunately he has a reputation of being rough with calculators. In the same period of time he has gone through about twice the calculators I have. Calculators have been stood on droven over and one left out in a field. He finally remembered that he had left the calculator in the field and when he returned he found that a bush fire had been through and burnt the calculator.

I have keept some of his calculators; the ones with damaged screens. They work in a sort of a fashion.

Getting back to the HP35. None of the keys work, where the charger plugs into the calculator is badly damaged, the charger is damaged and of course the battery pack is no longer usable.

I have often thought about trying to restore it, but I suspect that it is probable beyond restoration. I have never tried anything like restoration before.

Your talking about imersing parts in alcohol aroused my interest.

Just how hard is this all to do? I guess I cannot do any further damage to it. We are moveing office in a few weeks time. Already old stuff is getting thrown out. So I just might make the decision to bring the calculator home.


The HP35 is ridiculously easy to open and work on. I doubt that you will need to soak anything, as it can be completely disassembled so you can get at all parts to clean directly. By all means, take it home, or send it to me :-)

Take a look here and here for some disassembly information.

Good luck!



When I was first servicing DP equipment we used trichloroethylene a lot for cleaning but be careful it will dissolve some plastic, and adhesives. My brother is a survey technician and he told me that they used it to test pavement, they would use the trichloroethylene to dissolve the asphalt out of the mix.


I had very good results immersing my HP 41 in an optician's ultra sonic cleaner bath. No part of the calculator dissolved and after drying everything worked fine and looked like new.


Hm. I have a Branson ultrasonic jewelry cleaner. It's small but the printhead would fit...fill it with acetone, insert printhead, hope vibrations don't crack it...


Why acetone? The optician had a very soft cleaning fluid in it. It's the ultra sound that's supposed to do the job!


Acetone because you need some sort of organic solvent to have any hope at all of getting this goop off. 6 hours soaking in alcohol didn't do it; I suppose I could try ultrasound with alcohol first.


So...are these clean enough?


That looks pretty good. The resistive elements are naturally black. I'd just try it. If the some columns are missing when you print, then check it as normal (check the resitance of the element between the driver transistor and diode on the driver PCB, check the diode). If that all checks out, clean the head again. But I don't think that will be necessary


I find it best to immerse myself in alcohol instead :-)



After this post I decided immerse to myself in alcohol, I have noticed a reduction in accuracy of my calculations.

Interestngly this seems to be independant of the calculator used.


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