51-934 code 122 - Printable Version
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RE: 51-934 code 122 - RodB - 09-04-2025
Leave the meter attached to the plug prongs. This is so you can determine if removing the wire made a difference.
RE: 51-934 code 122 - philco4me - 09-04-2025
Removing the wire now reads 0
See pic
RE: 51-934 code 122 - RodB - 09-04-2025
Wrong! The circuit is open. You will have to learn how to read your DMM.
RE: 51-934 code 122 - philco4me - 09-04-2025
Sorry DMM ?
RE: 51-934 code 122 - RodB - 09-04-2025
Digital Multi Meter. How can we help you when you can't tell us what is really happening?
RE: 51-934 code 122 - philco4me - 09-04-2025
Yes I am trying to teach myself this Is the first time I had A short like this so it’s a learning curve. I will Reconnect the wire and test again. Thank you for your Patience
RE: 51-934 code 122 - MrFixr55 - 09-05-2025
EDITED 09/05/2025, 5:35PM, to add content and correct a mistake
Hi Philco4Me,
Sorry, I have been away from your thread for a while. Sorry, this will be long. Don't get discouraged, you will get this.
First off, for Ohms (resistance) on your DVM, OL means infinite resistance or open circuit or open switch.
A short (at least in a 120V power circuit) or a closed switch will read a reading close to 0.000 ohms.
Do this as an exercise:
With your DMM (Digital Multi Meter) set for Ohms, note that with your test leads not touching a device or each other, the reading will be "OL". This means that the reading is either an infinite resistance (a perfect insulator) or that there is a resistance that is higher than the limit of the meter (usually 20 Megohms). Now, touch the pins of the test leads together. You will get a reading of 0.00 Ohms. This is a dead short. If the reading is more than 0.00 Ohms but less than 1.0 Ohms, this is normal, but write this number down before taking measurements, and subtract this from the reading, especially if you need to accurately read the resistance of a device with low resistance, like a 10 Ohm resistor.
So, looking at your last pic, checking between the power pins, and having a reading of "OL" indicates infinite resistance.
WHEN WORKING ON THIS SET, PLEASE REMEMBER THAT POWER IS APPLIED DIRECTLY TO THE METAL CHASSIS! (You may have referred to this as a "frame".) Please avoid touching the chassis as a dangerous shock can occur. To be sure, close the power switch and using your ohmmeter, verify what pin on your power plug connects directly to the chassis and ensure that pin is in the larger of the 2 holes in the power outlet. However, with the switch off, the chassis becomes hot again through the tube filament string. this is because the power switch is on the "Neutral" side of the power, between tghe power cord and the chassis. THEREFORE, WHEN CONNECTED TO POWER, PLEASE PERFORM ALL TESTING WITH THE RADIO'S POWER SWITCH ON. WHEN WORKING ON THE RADIO OTHER THAN MAKING MEASUREMENTS, DISCONNECT THE POWER CORD FROM THE POWER OUTLET. DO NOT RELY ON TURNING THE RADIO'S POWER SWITCH OFF TO MAKE THE RADIO SAFE FOR CHANGING COMPONENTS, ETC.
Next step:
With the tubes removed from the set, with those 2 devices that connected directly between the power connector and chassis ground and the rectifier wires disconnected (From your last pic, it appears that you did this), measure the resistance (Meter on Ohms) between the 2 pins of the power connector. What is the reading? If the resistance is higher than 500-1000 Ohms, or slowly increases, then connect to dim bulb, apply power and you should see that the bulb may have shown some brightness but should dim out quickly. This would correspond with charging of the power supply filter caps. If still a bright bulb, unplug the radio and cut the wire between the Selenium rectifier CR1 and the 22 ohm resistor (the "load" side of the rectifier). If the bulb is off now, the short is "Downstream" of the power supply (solder splash, shorted electrolytic capacitor, capacitor installed reverse polarity, etc.). If the bulb is still bright, cut the other wire to the rectifier. If the bulb is now out, the rectifier is shorted to chassis ground. Note the outcome of these tests and post in this thread. I recommend that you replace the rectifier with a 1N4007 these are available from any electronics supplier, eBay, etc. for pennies each. Please note that diodes and electrolytic capacitors have polarity. We will discuss that after you post the outcome of your tests.
Again, sorry for the length of this post. However, this will be a good learning experience. Unfortunately, the issues that you are having with this radio are your "baptism by fire". Again, please heed my warnings posted in CAPS, but don't get discouraged! Like an old Home Depot commercial said, "You can do it. We can help."
Good luck and keep us posted; we are happy to help!!
RE: 51-934 code 122 - philco4me - 09-05-2025
Thank you for the reply. I will work on this over the weekend and post results. Thanks again.
RE: 51-934 code 122 - philco4me - 09-06-2025
I did some testing as you posted and did change the rectifier as I was not sure the reading was good. I thought better to just change it. The short seems to be where the safety cap is attached (see pic). I will also Attach the meter reading. I will continue to keep testing and thank you so much for that post.
RE: 51-934 code 122 - philco4me - 09-06-2025
I have a feeling that safety cap is not on the correct pin. Not sure if someone else had made a mistake and since it’s a 122 code I can’t be sure. The old part was a Philco .47 plastic cap that I had Never seen before
RE: 51-934 code 122 - philco4me - 09-07-2025
Good news. I found The short. A brand new safety cap was the issue so for now I have The .47 in place for now. Now when I turn it on I have Nothing. Tubes do not light up I still have to reconnect the light but I don’t think that has anything to do with it. All new electrolytes have been checked and replaced.I will Keep trying but some progress is being made. Thank you all for your continued help
RE: 51-934 code 122 - MrFixr55 - 09-07-2025
Hi Philco,
Progress! Great! The pilot lamp won't make a difference in whether or not the tubes light up as it is a standard 7 Watt 120 Volt night light bulb. However, having it in may be of diagnostic help.
Don't worry about the safety caps, leave them out for now. The purpose of these safety caps is to filter out any interference on the power line to the radio or any interference generated by the radio from entering the power line. The reason why they are called safety caps is that they are not supposed to short or overheat when across a power line. Having been bitten by a chassis that went hot, I can tell you that the original EMI filter caps were not safety caps. The radio will work without them.
For the next phase of testing, you will need to be taking measurements on a live radio. REMEMBER SAFETY. REMEMBER THAT THIS IS A HOT CHASSIS! Use the "one hand in your pocket" technique. In other words, to prevent a dangerous shock, wear non-conductive rubber soled shoes, sit on a non metallic chair. If you have not reconnected the rectifier wires, do this. If you replaced the rectifier, it is important that the side of the rectifier with the band (the cathode) be connected to the 22 Ohm resistor and the other lead goes to power.
Using an alligator clip, clip one lead to the chassis. Set the meter to AC, and with the radio power switch on and the radio plugged in, measure between the chassis and a known ground. The voltage should be essentially zero volts. If it is 120 V, reverse the plug. At this point, the pilot light should be lit. If so, you have power to the radio. If not, disconnect power and check the power switch. If you tripped the breaker testing the radio, the current that passed through the power switch may have been enough to blow it. With the radio unplugged, measuring across the power switch, you should read close to 0.00 Ohms. The meter should display a number, not "OL". If you read OL, then "jumper out" the switch so it is permanently on. The pilot light should light and if the tubes are all installed, they should light. If all else is well, you should get sound. If no sound and /or the tubes don't light, set the meter to DC and measure the cathode side of the rectifier, which connects to the 22 Ohm resistor. You should read at least 120V and likely much higher. If this passes and the tubes are not lit, it is because a tube is burned out. If all were well, each tube will have a voltage drop across its filament equal to the correct voltage of the filament. Think of a set of Christmas Tree lights. For example, a 50C5 will have a 50V voltage drop between pins 3 and 4 if it were lit. The 19C8 would have 19V across pins 4 and 5. The other tubes would have 12V across pins 3 and 4 except the 12AT7 which will have 12V across pins 4 and 5.
Set the meter to AC Volts, and with one lead still clipped to the chassis, use the schematic, and measure pin 3 and pin 4 of the 50C5. You should read 120V on both pins. If you read 120V on pin 3 of the 50C5 but 0V on Pin 4, then the filament of the 50C5 is burned out. If you read 0 Volts on both pins, you still have a wiring issue. If 120V on both pins 3 and 4, go to the next tube, the 12AT7 and measure pins 4 and 5. You should see 120V on both pins. If 120 V on one pin and 0V on the other pin, then that tube has an open filament. Keep working down the "string" in the order as listed on the schematic. When you find the tube that reads 120 on one pin and zero on the other, that tube has an "open" (burned out) filament.
To make things more complex, look at the bottom of the schematic where it shows the filament string. You will note that there are chokes in each side of the 12AT7 filament. In addition, there are several capacitors between various tube filaments and chassis ground. If the chock is burned out (open), this will cause the tubes to not light. If any of the capacitors are shorted, especially the one between the 50C5 and ground, it will burn out one or more tubes between the shorted cap and the source of power.
I know that this is complicated but do it one step at a time. Anything complex is made up of simple things. You cleared the short, now continue and find out why the tubeds don't light, using the above instructions in the order that I listed.
Do not be afraid to help, remember SAFETY, ask questions. We are happy to help you score a big success with this one.
RE: 51-934 code 122 - philco4me - 09-08-2025
Success. Tubes lighting getting static. I can Not thank you enough for guiding me thru this. When it’s all back together I’ll post a pic. funny enough it seem to start working when I replaced the light bulb. Again my thanks for your patience
RE: 51-934 code 122 - MrFixr55 - 09-08-2025
Hi Philco,
Is this a Christmas tree style light or a miniature 6 volt one? If memory serves, this is a 122 and you could only find a 121 schematic. If this is a 6V miniature bulb it may have been in series with the heater string but with a resistor bypassing it. If it is a Christmas tree style bulb it should have nothing to do with the filament string. If you dare and if it is a Christmas tree style bulb (or the lower wattage indicator type bulb with the same "candelabra" base as the Christmas tree bulb) remove it and see what happens.
Check all solder joints and connections to ensure that they are good mechanical connections where solder flowed well but not to the point that it "bridged" over to another connection.
Congrats on the progress and keep posting!
RE: 51-934 code 122 - bridkarl - 09-08-2025
Just a thought -- my multimeter has the option -- which was $10 extra - for extended probes. These extensions are a good idea I think -- they keep my hands a little further away from the chassis. Handy for testing resistors layered down in the radio. Just noting from the pictures of the multimeter in place.
As to this project -- I replaced the 120 volt "christmas tree" style bulb with a C7 Led bulb. Works fine. Not sure that's an option here, but it's much less heat and lower wattage and will never have to be replaced.
I also noted what looks like a silicon rectifier in the corner there. Might be worth looking at. I also tend to plastic sleeve cap leads. Probably overkill, but it looks good and prevents any accidental shorts when caps are next to each other, the chassis. I think this is on the right track overall. Looks good.