My latest problem involves a "restored" Philco 42-PT95 (i.e. recapped by Atlas Audio in Pittsburgh)
Above 900 Khz the radio works fine, tunes nicely and has quality sound. Below 900 Khz, when the tuner is moved, static comes out of the speaker. When you stop, the static stops.
Additionally, I can't seem to tune any stations below 900 Khz.
I have emailed said company, but I am hearing silence from them. I may be on my own on this one.
Probably one of the rotating plates on the tuning capacitor is rubbing against the stationary
plates. (Rotor shorting stator) If you slip a piece of paper between each pair you will find out which one is touching when the paper "grabs". It is most commonly the first or last plate of each section that is involved, and the cure is to ever so slightly bend the rotor in the opposite direction. Also, this exercise will dislodge any dust or foreign mater that could give the same symptoms. Works 99% of time.
OK so here is my latest adventure. I am hoping someone can give me some guidance or at least some explanation as to why it has happened ?
I did what was advised and passed a piece of paper through the variable capacitors (tuning capacitor). This helped. Instead of getting cracking static below 900 kHz [and no stations below 900 khz], this move to 700 Khz, and I was able to tune stations in that 700 - 1600 range. Additionally (and this is important) all stations were located at the correct dial position. In other words when I dialed 1450 the station at 1450 played.
I decided to use tuner cleaner on the tunning capacitor. Result:
- The cracking static below 700 disappeared
- Stations were no longer in the location they should be. For example AM 1450 was no located at about 800, 1390 was at 720, and 970 was no located at about 1100.
What has happed ? More importantly, how can I fix this ?????
Help .......
(This post was last modified: 10-30-2012, 08:55 AM by winkydink.)
Sounds like you over-sprayed and contaminated the trimmers or left behind too much coating on the plates on the tuning gang with residue - some cleaners leave behind a de-oxidizing oily compound, mainly usefull in switch contacts, but bad for a tuning cap or trimmer.
A non-residue cleaner is what you need that totally evaporates - many "tuner cleaners" leave behind lube compounds.
This residue changes the capacitance of the trimmers (or tuning sections) on the gang, throwing the alignment way off.
You'll have to carefully open the trimmers and clean the micas sheets and plates and re-align the set, it sounds like.
Can you point me to a link or web site that describes this proceedure ?
Stupid question, but I must ask. When you refer to the "trimmers" are you talking about the tuning capacitor.
Do I need to physically remove the tuning capacitor ?
What a mess, what a nightmare. I guess every mistake I make now is one less I will make in the future, but this has just been a terribly frustrating experience. Hopefully the damage can be undone.
Thanks again Chuck and everyone else for your help.
The trimmers are on one side of the tuning gang - usually one trimmer for each stator section of the gang. The non-moving plate sections are called stators (stationary) and the rotor is the moving halves of the gang.
BEFORE un-screwing each trimmer adjusting screw, COUNT the number of turns to remove it, so it can be put back in an approximate position so it will be close to current position and compression when re-alignment is performed. Otherwise re-aligning can be more difficult.
Removing the screw should let the top/outer plate lift enough to get the micas sheet(s) out to clean and also clean the bottom and top plates before re-assembling. Also clean any residue on the bakelite or fiberboard stator brackets holding the stator plate sections in the gang frame.
Use isopropyl alcohol that does NOT contain glycerin, i. e. "rubbing" alcohol.
As far as the gang plates, I'd use a fully evaporating cleaner, isoprop comes in spray cans too, which would let you flush the rotor and stator plates. Just a couple drops of light oil on the two rotor bearing would be in order too, since the alcohol spray will remove any lubrication there as well.
You may have to un-wire and remove the gang from the chassis if you cannot access the trimmers to clean.
The gang and trimmers should clean up fine for re-alignment.
If you sprayed on those, they need cleaning, ONLY if you sprayed them.
If not, do NOT touch them and only clean the tuning plates that you did spray. Hopefully this will help. Otherwise you need to take it to your local antique radio club meet and have it looked at.
* With regard to "non residue" "fully evaporating" cleaner, the only isopropyl alchohol spray that I can find (internet search) is a hand pump spray. Is this what you are refering to ? Is there other type/brands [Deoxit ?]. Most tuner/cleaners (as I have found out) contain some type of oil or lubricant which is what got me into this mess in the first place.
* Assuming that I can clean the mica and upper lower plates of the trimmer and the gang, basically what are my steps. [I have been reading and want to be sure that I am on the right track]
- remove the trimmer screws and count number of turns it takes to remove each screw.
- clean mica and upper/lower trimmer plates with fully evaporating cleaner.
- clean gang with fully evaporative cleaner
- reassemble gangs and put screws back in using the same number of turns that it took to remove them
- begin realignment proceedures.
- where exactly are the rotar bearings.
* With regard to realignment. Some questions.
a) Do I adjust the trimmer screws at any time during the realignment [Is this done first, before the adjustment of the IF transformers ?]
b) Is there any article on this Phorum or your site that is a "Realigment 101" ?
It is a learning process. I have dug myself a hole about 10 feet deep, I am trying to claw my way out.
Thanks again for the help.
(This post was last modified: 10-31-2012, 07:58 AM by winkydink.)
Isopropyl does come in aerosol spray cans.
Try Mouser Electronics, DigiKey, MCM Electronics, etc.
A pump will not be forceful enough. Cotton swabs will also help scrubbing between the plates. Careful not to bend any plates.
You have the cleaning steps basicaly correct - work slowly and take your time.
If you do not have the test equipment and service info to re-align a set, you need to have someone do this, like a local club member or the club may offer services. You have to follow the alignment steps in the service manual.
Sounds like you need to hookup with someone at a local club to help you learn this. It's a "hands-on" kinda thing and just reading about it won't make much sense. Having some electronic knowledge/experience is a plus.
I agree about the local club aspect. Unfortunately I am in central PA and the closest clubs are in Harrisburg (2 hour drive) and Pittsburgh (3 hour drive), so no easy solution with regart to that. I will see how close I can get and possibly either farm it out or seek some advice over thanksgiving with some relatives.
I have received the Isopropyl aerosol in the mail yesterday [from Mouser Electrontics], and plan on attempting to undo the damage that apparently I have done.
Stay tuned.
(This post was last modified: 11-08-2012, 01:20 PM by winkydink.)
Well, if you didn't touch them yet turn down until closed, record exactly how many it turns and fractions it took. Then you can untuurn and completley disassemble, carefuly clean up the fragile mica pieces with rubbing alcohol, lt the pieces dry overnight, put it back together tight, then back off from your notes. You should be pretty close, but for sure an alignment may be helpful.
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