[jcassity]

if you have spare circuit boards lying around like i do,, try to harvest a variable cap off one of them... three leg usually a white rotator and blue body ,, that color code i think designates pico ferads... but either way, i used the same process to narrow down a faulty IF variable cap.

I only have a few resto's under my belt since joining here and i have already ran into 3 bad IF's but all three had to do with tuned slugs.

if you have a way to measure the capacitor size or by part number,, target the specs of C300A as your cap that you would want to duplicate into the spot of C301A.

[criageek]

Ok, I'm back to the FM oscillator theory.  I removed Z301 and everything looked ok. I disassembled and cleaned all the trimmers and while I was in there I replaced the 300pF mica cap and installed all new wires.  I also replaced C308 and C310 while I was at it.   I reinstalled the IF can and just tacked the wires in place in case I needed to remove it again.  I went through the entire AM and FM IF alignment procedure and it went well.  A couple of the trimmers are at the end of their limits, but I assume that's because I left the wires longer than they should be and there is some stray capacitance.  But everything aligned properly and C301A can be peaked as it should be.

But I still cannot get a signal through the front end.  When I just try to tune from one end to the other on the FM band there is absolutely no indication that the tuning cap is being changed...no change in pitch or volume...no squealing...nothing.

I recently read somewhere that I should be able to inject a signal to simulate the local oscillator.  I haven't been able to find that post again.  How do I go about doing that?  I know it needs to be 9.1mc above (or is it below?) the tuned frequency, but where should I inject it?  How strong does the signal need to be?  Directly injected or through a cap?  If I can tune a station this would tell me that the local oscillator in the radio is not running.

EDIT:  I should add that step 2 of the FM tests I referenced above still fail.  A signal will go through but it's a much lower signal than at step 1.

Thanks for the help!

Rich

[jcassity]

back to your post #150
-your higher AM and FM voltages are understandable because your prints will say the assumed utility voltage operation,, lets assume your prints say 117vac.

depending on the time of day and other factors, your utilty line voltage is higher than in 1947....lets assume you have 124vac. the percentage increase is what
you are seeing.


to your current post...........
I see two sets of FM instructions from post 141 and 150.
it appears the instructions from post 150 continue from the steps in post 141,,,, both start off as "STEP 1" ,, confusing.



on an FM set i just worked on,, down near the power input there is a cap off the HOT leg of power tied directly to ground.
parallel to that is a single wire spade connector hanging in the wind.
the instructions say to tie this wire directly to the FM termainal of the radio.
long story short,, the radio does not have a built in FM antenna ,, *BUT** it uses the actual power cord Line 1 or L1 or hot leg,,, as a "default" FM Antenna incase you dont have an external one on hand.
i am going to backpedal your posts to see if i see your FM being able to use an alternate means of signal reception other than an aerial FM.
reason i bring this up is on my set, with no external FM antenna hooked up, the radio got a lot of FM reception and thats because the power cord hot leg is the other antenna.
what this means is the power cord should be approx 56'' long to come close to the FM recpetion capability. Obviously the ground or return ref signal depends on the N leg to complete the antenna circuit.

In your case,, i am hunting down all the band selector switches "showinng" the FM selection is wired, then tracing out that path.



here is what i may try...

connect your box antenna back up,, or any other two lead antenna to duplicate normal FM operation needs.

set a small modern radio next to your set and tune to a station that comes in on FM.
power up your philco which is set to FM.
rotate your philco tuning cap to see if your philco interrupts the reception of the modern radio.



shut off moodern radio leaving the philco on.
adjust your sig gen to the frequency of the station that came in strong.
loosely wrap a few turns of insulted wire round your box antenna.
connect your sig gen to this wire you will have stripped back a tad.
turn up the vol on the philco set.
rotate the tuning cap left or right in an attempt to "hear" the sig gen signal,, hunt it down.
or..............
rotate the sig gen left or rith to "hunt down" were this signal is actually at on the philco.


it looks like you have a pair of wires factory installed from the 4 position terminal block.
with power off......... and with FM selected............
see if you have continuity from the 4pos terminal block terminal 4 to chassis.


jumper wire around C410 near L405 on your prints.
check you have less than an ohm from the 4pos terminal block terminal 2 out to pin 5 of the 6AG5.

[willydcamaro]

Hi Rich, I'm still having a hard time with this chassis. Do you have any before photos of the chassis ? Thank you,Bill

[Greggshere]

Here are a few shots of my 47-1230 Code 121 before I did anything to it. Maybe they can help some.

               

[willydcamaro]

Wow!! Exactly what I need. Thank you very much! Bill

[Greggshere]

Glad to help! Good luck!

[criageek]

Thanks for the great pictures Gregg! Those I posted are the best 'before' shots I have of the whole chassis, but the output transformer, bakelite capacitor block, and phono cord have been removed. In the first shot I've also removed the tuner sub-chassis. I do have several good detailed photos of various sections but nothing that shows the entire chassis before I started working on it.

Good luck Bill!

Rich

[willydcamaro]

Thanks again Rich and Gregg !!

[willydcamaro]

Hi Guys, do you have a picture of how you redid C102 and C103 ? Thanks, Bill

[criageek]

Hey Bill - I documented how I restuffed mine here: http://philcoradio.com/phorum/showthread.php?tid=16421

Rich

[willydcamaro]

Very well done Rich. Unfortunately I put new caps under the chassis already. Thank you again.Bill

[criageek]

Hey jcassity - thanks for all your help!  I haven't been ignoring you...just getting around to replying.  I'll try to cover all your points.

"...your utilty line voltage is higher than in 1947....lets assume you have 124vac."  I'm driving the radio with my variac set at 117v

"I see two sets of FM instructions from post 141 and 150."  Sorry about the confusion.  The Philco documentation has a set of AM tests.  If it passes those you move on to the FM tests that I referenced in post 150.  If either set of tests fail you move on to more troubleshooting tests.  The subsequent FM tests are referenced in post 141.

"i am going to backpedal your posts to see if i see your FM being able to use an alternate means of signal reception other than an aerial FM."  I don't think my radio uses the power cord as an antenna.

"set a small modern radio next to your set and tune to a station that comes in on FM."  I tried this but didn't hear any kind of difference in the modern radio when I tuned through the FM band.  I think this is just more evidence that the local oscillator is not running.

"it looks like you have a pair of wires factory installed from the 4 position terminal block."  I'm not following what you're referencing here.  What 4 position terminal block?  EDIT:  Just after I typed this it dawned on me that you must be talking about the connector for the FM antenna, right?  If so, yes, I do have continuity from pin 4 to ground.  I'll have to jumper across C410 and do that test later.

Thanks for your help...I appreciate it!  I'm still hunting.

Rich

[criageek]

Here's something else to throw into the mix.  I decided to try to clean the function switch as well as I can...all of the contacts are black.  I don't think this is causing my FM problem because I can see tracks on the flat rotating contacts where the stationary contacts ride on them.  But it can't hurt to try to clean them up a bit.  Anyway, as I was cleaning the rear side of the front section I noticed this:
   
It's cracked at the top. And it's definitely broken...I can move it.  I also don't think this is causing my FM problem but it certainly needs to be fixed.  I cleaned the area as well as I could with some 91% alcohol.  So, what's the recommended glue to use?  I'm thinking super glue but want to get recommendations.

Thanks,
Rich

[Phlogiston]

https://www.russoldradios.com/blog/whats...can-happen

Note Harry's comment at the bottom.

Russ