Welcome Guest! Be sure you know and follow the Phorum Rules before posting. Thank you and Enjoy! (January 12) x

Thread Closed
Thread Rating:
  • 0 Vote(s) - 0 Average
  • 1
  • 2
  • 3
  • 4
  • 5

Zenith 7H920 AM but no FM
#1

OK, here's my latest project. I replaced all electrolytics and wax/paper caps. Checked and replaced all resistors. Checked all coils. All tube test good.
AM sounds great. FM just hums. While turning the dial, I was able to disrupt reception on an FM radio on my bench. So I guess the oscillator is working. I checked the AM/FM switch (had a problem with one on a Philco once) and it appears to be OK. Any ideas where to look?
Here's the schematic: http://www.nostalgiaair.org/Resources/312/M0025312.htm

Thanks,
Eric

Eric
The Villages, FL
Member: Philco Phorum, ARF, ARCI & Radiomuseum.org

#2

Before any of the below is considered, you may want to clean all the tube pins and sockets by using DeOxit or similar and rocking the tubes a bit in the sockets. FM is very picky about signal path.

My first suspect would be the 19T8. These have in my experience a very high H-K leakage failure rate. If you have a scope and an isolation transformer, I would trace the signal beginning at the input to the 1st IF and go downstream from there until you lose it. If it's not there at the 1st IF, then you may need to replace the 12AT7.
#3

Thanks. I'll check this out and get back to you.

Eric

Eric
The Villages, FL
Member: Philco Phorum, ARF, ARCI & Radiomuseum.org





Users browsing this thread: 1 Guest(s)
[-]
Recent Posts
Testing a speaker and output transformer Trutone A2-G
Would an output transformer if weak, cause the problems I am seeing with lower B+ voltage? murfmurf — 01:22 PM
Testing a speaker and output transformer Trutone A2-G
Hello murf! I merged the threads. Please do not start new threads regarding the same radio. Take care, - GaryGarySP — 10:21 PM
Philco 42-345 Restoration/Repair
Regarding picture 5 on page 1 of this thread this capacitor is #40 on scematics diagram - 4mF+4mF. Black wire is "-...Vlad95 — 09:01 PM
Philco 42-345 Restoration/Repair
That's a dual 4 MFD, red and green are both 4mfd and black is common negative. You should be able to see them in the pow...RodB — 08:58 PM
Philco 42-345 Restoration/Repair
Can anyone help me figure out a capacitor that has 3 wires coming out of it red and green on one side and a black wire o...osanders0311 — 08:14 PM
Two small radios from France. Restoration and review.
Greetings; I think that it's possible that the assortment of components was the result of post war parts shortages, a...Arran — 12:18 PM
Philco model 38 code 121 not receiving signal.
Unfortunately I can't inject any audio into the volume control. It is in the primary circuit of the antenna coil, not in...Stormlord5500 — 09:32 AM
Philco model 38 code 121 not receiving signal.
Sounds good Gary I'll do that. I have plenty of stuff like that I can scrounge up. I am still kind of new to all this so...Stormlord5500 — 08:47 AM
Philco Battery-WWII vintage
Seems to me that this a general purpose or radio filament 6V battery of very high amp-hour capacity and very high "...MrFixr55 — 08:08 AM
Philco model 38 code 121 not receiving signal.
You should be able to inject an audio signal such as from a CD or mP3into the radio at the volume control. The set will...MrFixr55 — 08:14 PM

[-]
Who's Online
There are currently 262 online users. [Complete List]
» 1 Member(s) | 261 Guest(s)
Avatar

>