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2385 reconnect PS00 to P400 pin question
- Thread starter sendust
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I reversed the string on the fly wheel, and now im traveling in the right direction for station tuning. The fact that the fm worked for a while and was very clear and strong , confirms connection, now i only get loud rumbling but meters show signal strength, should i recap fm board P100?
Wait... when you tune the FM by moving the dial pointer, the signal strength meter goes up and down as you go past known strong stations?
Does the STEREO light come on for some stations also?
If both of these are YES, then it is not the P100 board.
You should not just blindly start recapping boards to find the problem. That will only make it worse because you can't tell if you introduce a new problem.
What else did you touch besides the string to make the FM go out?
I didnt touch anything but i had an issue on the PS00 board, a tech repaired a broken board in the past, he added wires to jump traces and a wire came off and i lost sound, i repaired the wire and replaced board, dial string had to be removed to get front plate off to allow removal of PS00 board, After repair AM worked perfectly and fm worked very clear for 5 minutes, then just dead air. dial still works ,everything else works. As far as tuning i just have to get the string refed properly, Dont know why ive lost fm, i tried the 75 ohm tap for antenna no luck. I just get a crackling sound on FM. Maybe a wire going to the PS00 board is an issue? Stereo light does not come on when moving dial, it did when it worked for 5 minutes. I forgot to add, i had an issue with AM light coming on when on FM, so both would be on, it turned out the board with the led light had a wire jumped from the AM JY20 sticking out and came in contact with chasis causing the issue,
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Here is a block diagram, red boxes are potential problem areas and green boxes have nothing to do with ONLY FM issues.
- fm worked very clear for 5 minutes, then just dead air
- Stereo light does not come on when moving dial, it did when it worked for 5 minutes.
- You didn't answer my question: "does your signal strength and tuning meter work for FM"?
- Make sure all of the buttons are OFF: Tape Copy (OUT), Tape Monitor (OUT), MPX Noise Filter (OUT), Multipath (OUT), 15kHz and 9kHz Filters (OUT), Loudness (OUT), FM Muting (OUT).
- Selector to FM (not FM 25uS), Tone Mode OUT.
- No STEREO light. Does the Tuning meter move as you move across the dial. (From you previous post "now i only get loud rumbling but meters show signal strength")
- Turn MUTING LEVEL control on the back of the receiver CCW to MIN.
- Look for any wires that you may have knocked off when you were fixing the dial string.
Thanks i will check all wires today. The tuning meter moves as you move across the dial, dead air a little louder when on a station, the dead air is sometimes a loud rumble sound. I tried FM this morning ,loud rumble, i moved the dial and on one of the stations i could hear some talking faintly, so i stopped on it, then it came in to about 20 percent and got stronger, then it faded out and only rumbling again. Almost sounds like it cant pull in the station.
There is little chance a wire is off, checked all connections, also if receiver is off for a day or so FM partly works for about 5 seconds, it seems what ever pulls in the station is defective. I want to recap the FM front end board but im not sure where it is, the boards are not marked in this unit. Can you direct me where this board is ? thanks pete
The FM Front End is the P100 board and looks like it is located on the FM tuner capacitor (bottom right of the diagram below).
You may not be able to easily get to it and I'm not so sure that is the problem so unless you definitely know it is an issue, I would leave it alone.
Looking at the schematic, there are no electrolytics on the board to recap (see schematic below). Why do you want to recap this board???
Not sure if the FM was working, i never use it, I was just testing all settings after some repair and AM was fine FM was good for about 5 min then faded out to the rumble , Phono 1 and 2 and Aux perfect. It seems if i leave it off for 24 hrs i get a bit of FM for a few seconds ,so it seems whatever pulls in the FM is defective, Where is the variable cap? Just realized what the variable cap is, if im correct its not something that i can clean, if it was deflective ,would it not affect AM
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I thought the frond end fm pulled in the stations, I guess i am mistaken.
They look very clean but i took a qtip and dipped it in Doxit 5 then touched the points above the fins, i worked the wheel about 25 times ,then used a clean qtip and dried the area off, then i powered up and tried the FM. still noisy no signal, i ran the wheel back and forth for about 10 times and suddenly a station came in vey strong for about 10 seconds, then disappeared again, I tried back and forth for another 5 minutes but no luck. Something makes the station return once in a while, so im sure its not a loose wire. pete ps i did not touch the fins, not sure i should clean them or even know how
Does what i have described sound like a faulty small signal transistor, if so would that be on the p200 board? pete
I have a few antennas but i am using the ribbon type for now, ive tried it on the 300 ohm screws, ive tried it on the 75 ohm screws. makes no difference, i get the same signal on the meter when passing a station. Also im not sure but if it was just the antenna would i get the loud thunder,crackle sound that increases and decreases even if you dont move the dial.
That sounds like it might be a transistor going bad, but I don't know for sure. The problem is trying to locate it.
What kind of test equipment do you have and are you experienced in troubleshooting electronic circuits?
Also, each type of antenna is connected to the receiver differently and if you don't connect it to the correct input, it won't work.
When you say "ribbon type" do you actually mean 300 Ohm dipole antenna?
Yes, thats the type i have. If i know what to test i have good analog meter like simpson and digital Fluke meters. I rebuild tube amps for juke boxes and have recapped many stereo amps, but as far as using an oscilloscope , i own one but dont know how to use it properly. I can test for values and voltages if i am directed where to look.
