I have an old Magnavox stereo that the FM doesn't work everything else works. So far I've recapped the FM board still doesn't work. I've checked the voltages on the board by this picture and pin 2 is supposed to have -15v but it has -20v all the other voltages are right could this be what's causing the FM not to work?
>>2997666Did you connect an antenna, Satan?
>>2997703I did I also didn't notice that you check that in AM mode so it is -15 only in AM mode so that's not what's wrong with it
>>2997794Make sure the variable capacitor is clean and moving freely with the tuner dial. Clean all switches and pots with contact cleaner. Check solder joints and reflow anything that looks broken.
>>2997666>FM doesn't workAs in no noise at all or just static?
>>2997837No noise at all
>>2997805I'll do this when I get off work
>>2997840You get sound out of it in AM mode though, right?
>>2997961Yes the AM radio works fine so does the phono
>>2997964Did you fix it yet?
>>2998122no
>>2998285Have you tried the "pencil method" ?Louis Rossman on YouTube has a video about a faulty speaker output on an amplifier. It's a common practice at old tech shops here in México.
>Get a second FM radio and put it next to it.>Tune the working radio between stations at the top end of the FM band (repeat at bottom end of the band if that doesn't work).>Put the non working radio into FM mode and tune up and down>See if you can hear the local oscillator 10.7 Mhz above of below on the working radio.If you can hear it that rules out that part of it at least.
>>2998285Did you clean the selector switches and reflow their legs? The power supply and amp are working, so just focus on the FM circuit. Probe for voltage readings at the transistor collectors in each FM stage. If you don't get a voltage reading then there is an open circuit or bad ground somewhere (possibly bad switch or broken solder joint). Otherwise a component failed or went out of tolerance.
>>2998319When I do this the other radio will go quiet at around 96mhz every time I go through the broken radios tuning
>>2998321I've checked the voltages at the transistors and they are all close to the diagram
>>2998349Then the FM local oscillator is working in the broken radio. Good.With an antenna connected do you get any stereo indicator when you tune passed stations or any voltage variations on the base of Q11? (Don't go turning trim pots)?
>>2998381>when you tune passed stationsI should add they must be stereo stations for this to work.
>>2998381>>2998382So this diagram I got doesn't exactly match the other boards in my stereo so i don't know where Q11 is I think its on this board while I had it loose I changed the caps on it and I now can tune in FM radio stations but its not very loud and the stereo light doesn't light and tuning gauge don't move at all when tuning. But this is a massive improvement. The stereo light comes off this board the tuner guage off the tuner board.
>>2998381>>2998382>>2998435this is what the diagram shows witch board Q11 would be on and its alot diffrent then mine
>>2998436forgot the picture
Update I just went ahead and recapped everything. Now everything works excepted the tune meter in FM mode it just moves a little it does work in AM mode and the stereo light doesn't work I can probably live with that. I should have just went ahead and recapped everything from the start I just didn't want to make another problem before solving the first problem.
>>2998435As my eyes have gotten poorer, one thing I like about old electronics is how big everything was. Trying to read the bands on a modern resistor is a pain in the ass.One thing I don't like is how poorly documented a lot of their stuff was. When I rebuilt a Commodore 64 and an Apple II I was able find vintage documentation about just about everything. Entire books written about how to troubleshoot and fix the different revision. The documentation they have on those machines now? Shit, people have high resolution scans of decapped chips! Don't worry about finding component locations on some random board revision.Want to find out what fucking Philco used in a radio they sold fucking 2,000 units of? Fuck off. They revised the circuit board 14 times, none of which are remotely similar, but only documented the first one. The last three visions use Tesla valves and a mercury-arc rectifier.
>>2998473I just screw around with this stuff sometimes kinda just guess most of the time but every diagram I've found for an old stereo has not lined up exactly with what I was working on
>>2997666>and pin 2 is supposed to have -15v but it has -20vWhat is the voltage across X14 and what is the part number of X14, the zener diode?
>>2998791I think my meter was f'd on that one I checked it again after I posted that and it was -15 on AM. I already put it back in the cabinet it seems to be working great after I changed all the caps. Now I just need to clean all the old greese off the record player it has too much drag on the arm the needle won't track
