Sanyo Clock radio repair

[user_12345a]

Hello,

I am trying to save an older but very good clock radio.

It's a sanyo RM-7024.

The volume is very low unless I push hard on the volume adjustment. (which goes back a forth and isn't a knob) It works fine with the sure-wake (bypasses the volume control and gradually increases volume level in alarm mode) on but it gets far too loud for me taste.

First problem: I can't get to the volume control easily.

As shown in the pictures, the volume control is just below the face of the clock.

I don't know how to take the front off. There are a couple of screws going to the face plate but they're impossible to get to with a screwdriver. There's a plastic piece blocking which has all the controls (and a small pcb with buttons) in the way and it's screwed into the bottom of the main board which isn't accessible. I've tried undoing the screws holding the psb to the case with no luck.

Help?

 

[user_12345a]

Second question: Assuming I get to the volume control, how would I go about fixing it?

Would some contact cleaner work or does the volume control have to be replaced?

I would hate to throw it away. If it was a cheapo pos I wouldn't bother. They don't build them like this any more.

 

[hevans1944]

I would try spraying some contact cleaner into the front slot using the small plastic tube that can usually be afixed to the push-button spray head. Move the slider back and forth while spraying and try to get the tip of the spray tube as far inside the slot as possible.

Don't get too carried away and spray so much that it drips back out. Some of the contact cleaners are also not very kind to plastic finishes, so try to avoid getting any on the outside case. Spray a little, operate the slide back and forth, test to see if that worked. Repeat one or two times if necessary.

The problem with contact cleaner is it leaves behind the original residue that was causing the problem. After a few weeks, or years, or whatever, the problem may re-occur. If the initial application works and the volume control is restored to normal operation consider yourself lucky.

If the problem re-occurs, you can try more contact cleaner, but I would then consider soaking just the electronics end of the clock radio in a bath of 99% (anhydrous) isopropyl alcohol. Do not immerse the loudspeaker end into the alcohol. Slosh it around for several minutes in a plastic tub filled with the alcohol. Drain as much alcohol as possible when you lift it out of the "bath" and then let it air dry for several days before applying power. You can also use a can of "compressed air," such as those used to clean computer keyboards, to blow out as much alcohol as possible to help with the air drying, but do not neglect the three or four days of air drying before applying power.

The alcohol soak is a "final resort" treatment to save your clock radio. Use at your own risk. I have used this method (successfully) to clean electronics circuit boards and such, but it is a gamble with something that has moving parts (like the tuning dial mechanism) that may lose lubrication and stick or bind afterward. Instead of full immersion, you may want to try squirting alcohol into the slot and letting it drain back out. Again, air dry for several days to make sure all the alcohol has evaporated before applying power.

Be careful around the alcohol, which is very flammable. No smoking. No open flames of any kind, including pilot lights. It is best to perform the alcohol bath outdoors where there is plenty of ventilation. The used alcohol can be disposed by simply pouring it on the ground where it will quickly evaporate. If you can't find anhydrous alcohol (normally sold in five gallon buckets at chemical supply houses), most drugstores carry 91% isopropyl alcohol (used to clean skin prior to insulin injections). Avoid the "rubbing alcohol" concentrations, which are generally around 80% alcohol content, as these evaporate too slowly and do not dissolve hydrocarbon residue as readily.

 

[user_12345a]

The volume control isn't an open hole - there's a plastic piece in front which moves with the level or whatever it's called. Not sure if anything would actually get to the control.

 

[davenn]

The volume control isn't an open hole - there's a plastic piece in front which moves with the level or whatever it's called. Not sure if anything would actually get to the control.

its an open slot that the slider moves back and forward in





Dave

 

[user_12345a]

There's no open hole on mine - there's a plastic piece which moves back and forth with the lever.

 

[davenn]

There's no open hole on mine - there's a plastic piece which moves back and forth with the lever.

yes that's correct and what do you think that lever moves in ?
That plastic shield is to slow the entry of dust etc into the pot it probably doesn't extend the whole length of the pot in each direction
and if you look carefully you may find where you can squirt in cleaner when the lever is at one end or the other

Dave

 

[hevans1944]

You need to use some common sense and a bit of creativity here. Perhaps a hypodermic syringe and a longish blunt needle will allow you apply contact cleaner more precisely. Again, a little bit goes a long way.

I think we are done here. Thanks @davenn for the nice photo of the linear potentiometer.

 

[user_12345a]

Success - at least for now. I sprayed contact cleaner around the volume control from the outside and internally as well.

I did mess up the casing a little bit and the cassette mount.

Thank you.

 

[user_12345a]

It didn't last long.

The problem came back.

What is the next step? Is 99% alcohol expensive?

 

[hevans1944]

You can get by with 91% isopropyl alcohol. Cost is a few dollars a quart. Just be aware that as soon as you open the bottle it starts to absorb moisture from the air. That means an open bottle doesn't remain 91% for very long!

Anhydrous 99% isopropyl alcohol is not normally available over-the-counter. When I used it, I bought 5 gal. drums, usually five at a time, from a local chemical supply house. I don't think it was very expensive, but what would you do with five gallons of the stuff? Anhydrous alcohol absorbs moisture from the air even more rapidly than 91% alcohol. You may find it sold in smaller containers, but I would try the drug store stuff first. Be aware that so-called rubbing alcohol is somewhere around 80% alcohol. Don't use that on electronics because it takes forever to evaporate and doesn't dissolve gunk as well as the more concentrated variety.

 

[Gryd3]

You can get by with 91% isopropyl alcohol. Cost is a few dollars a quart. Just be aware that as soon as you open the bottle it starts to absorb moisture from the air. That means an open bottle doesn't remain 91% for very long!

Anhydrous 99% isopropyl alcohol is not normally available over-the-counter. When I used it, I bought 5 gal. drums, usually five at a time, from a local chemical supply house. I don't think it was very expensive, but what would you do with five gallons of the stuff? Anhydrous alcohol absorbs moisture from the air even more rapidly than 91% alcohol. You may find it sold in smaller containers, but I would try the drug store stuff first. Be aware that so-called rubbing alcohol is somewhere around 80% alcohol. Don't use that on electronics because it takes forever to evaporate and doesn't dissolve gunk as well as the more concentrated variety.

@hevans1944 , what about this stuff? -> http://www.thesource.ca/estore/product.aspx?product=4408726&language=en-CA

I've looked at the 'ingredients' and if I remember correctly it contains isopropanol, (bu|pro)pane and a couple other chemicals.
I've used it mostly to clean off gunk and button contacts and it seems to dry pretty quickly.
Ideas?

 

[hevans1944]

I have never used the product, but it looks like a typical electronics solvent. My favorite is a 50-50 mixture (by volume) of 99% isopropanol and trichlorethylene (TCE). Unfortunately TCE is banned from use for electronics cleaning now. In the Air Force we would soak 20mm Gatling gun barrels in a heated solution of TCE to clean them. It was widely used as a hot-vapor de-greaser and solvent in the electronics industry, especially for PCB manufacturing. And it used to be sold mixed with isopropyl alcohol as a general electronics solvent for flux removal and cleaning. Like all aromatic hydrocarbons, TCE is toxic to breathe and must be used with adequate ventilation. That's assuming you can get your hands on any of it. You might have better luck trying to buy chlordane than you would TCE. Of course chlordane does not work as a contact cleaner, but it's death to termites if you can find it.

My recommendation to the OP was to use a "bath" of isopropyl alcohol to dissolve any gunk left behind by other contact "cleaner" products. Dip it, slosh it around, drain it. Allow to air-dry for several days until all the alcohol has evaporated. After that, he may want to apply CAIG DeoxIT Fader F5S-H6 Spray, available here, to restore lubricity to the slider potentiometer moving contact. I've never used this stuff either, but it looks like it would be a good idea to do so after the alcohol bath cleaned away most or all of the gunk.

There is another DeoxIT product that the radio amateur community swears by for use on antenna coaxial cable connections, DeoxIT metal cleaner. DO NOT USE THIS ON THE SLIDER POTENTIOMETER!

 

[user_12345a]

to restore lubricity to the slider potentiometer moving contact.

Does alcohol damage the potentiometer/De-lubricate it?

 

[user_12345a]

I think i'll skip the tce - sounds like nasty stuff.

 

[hevans1944]

The alcohol will de-lubricate the slider interface to the potentiometer as it dissolves and washes away whatever junk has accumulated. That's why you should follow up with a little bit of CAIG DeoxIT Fader F5S-H6 Spray after cleaning. This will add a small amount of lubricant, but hopefully not enough to trap more contaminants. The alcohol should not cause any further damage to the potentiometer, but if the contact and/or the surface it slides on is already damaged (usually by trapped debris) then it may not help either. This is truly a last resort remedy when "conventional" contact cleaners fail to provide a permanent repair.

These slider-type potentiometers usually have a special audio logarithmic taper that allows the loudness to appear linearly proportional to the slider position, since human ears have a logarithmic response to sound pressure levels. This taper is created by the underlying conductive strip, usually a plastic material impregnated with conductive carbon, to which the slider makes electrical contact. The material does eventually wear out, but that requires tens of thousands of back and forth trips of the slider contact across the conductive surface... unless there is abrasive debris present to accelerate the wear. That is the purpose of the alcohol cleansing: to remove contaminant particles.

If alcohol cleansing followed by re-lubrication does not provide a permanent repair, the slider potentiometer will have to be removed and replaced. It may be difficult to find an exact replacement because of the age of your radio.

 

[user_12345a]

I take it regular contact cleaner doesn't lubricate?

Would silicon lubricant work if I can't find what you recommend - like this stuff: http://www.canadiantire.ca/en/pdp/3-in-1-silicone-spray-0381562p.html#.VPyHQ6KfrEc

Between the contact cleaner, lubricant and alcohol, it could cost more than a new clock radio.

 

[hevans1944]

Regular contact cleaner does lubricate. It contains both a solvent and a lubricant.
Do not use any kind of silicone lubricant on electronics moving parts, such as your slide potentiometer. The silicone residue is a non-conductor that IMO adds nothing.
You probably cannot purchase a new clock radio that is as nice as the one you already have. But that's your call.

 

[user_12345a]

I saturated it with contact cleaner - now not only is it very soft, it's crackly and has a high pitch noise.

Bad sign.

 

[user_12345a]

Is there a difference between automotive contact cleaner and circuit grade-cleaner/

I used something that i later discovered is for automotive use only, not circuit boards. Is this potentiometer doomed now?