-
Further along reading voltages and 1 current that seemed odd since the unit was off.
And it lead me to some questions as to how to take the readings.
I desoldered L3 and put the ammeter in series at the connection. It read -22MA even with the unit turned off. Is that usual ? And I dont know where to put the + and - probes, hence the -22MA. It could be +22MA.
And when I take the voltage readings on the top of the PCB, I dont know at which end of the component to place the +probe or the -probe with the other at ground. So sometimes I have been doing it both ways and indicating both of the readings and separating them with a comma. Like on the schematic that shows the transformer, C61 is 19 , .08 etc.
Where the 32V should be, it is reading 38V. I dont know if that is within tolerances or not. I cannot read datasheets to see wassup. The resistor R10, just before Q2 transistor 2SC1815, reads 38,8 with a drop of 29.4. I guess the sum=38 so all is well.
Q2 transistor 2SC1815 reads a 0000V on the base. Does that seem right ?
I took the readings at each pin of the IC, LM7000 and wrote them onto the hand drawn LM7000. The LM7000 is way obsolete so if it is faulty it will be difficult to get a replacement.
So, are these readings what are to be expected and where should I start looking for faults. I have been trying to trace the schematic, left to right, top to bottom, as that is what another site recommended. However that scheme seems to fall apart quite often.
Oh yeah, when I was looking at the FE407, titled U1 Front end, its a sealed box so its tough to get many readings although I took a reading at pin 6 and it was 2.85V. Pin 6 says OSC so is that supposed to be a sine wave and should I be able to read it using AC volts ?
Since the blowing fuses situation seems to be stable and I am getting the correct voltages out of the power supply,
except 32=38, do you think that I should start another thread since this one seems to be getting quite lengthy and cluttered with my early fumblings ?
Thanks again
-
Generally unless otherwise noted, all voltage measurements will be referenced to ground, so put the negative probe on a node indicated by the ground symbol and leave it there for measuring voltages unless you have a specific reason not to.
When you take current measurements the polarity on the display just depends on which way you've got the probes, generally you want to have it whatever way gets you a positive reading. There is not really any such thing as negative current but the indication can be helpful in that it tells you the polarity of the circuit.
38V seems high for the 32V rail, as I recall from the schematic it should be regulated. You might check and see if the pass transistor that is supposed to regulate that has shorted, or if you forgot to solder something back that you removed. -
Hoping the tunner section is not fried over 38V
-
Does it or can it make sense that the 22MA of current is present with the until switched off ?
Are some parts of tuners designed this way ?
Thanks -
Hoping the tunner section is not fried over 38V
Corom, is there a fairly easy way/reading that i can take that would tell me if the tuner is fried.
As I look at the display and try the buttons, the only one that doesn't work is the mode which I think selects AM/FM.
The others when I tried them seemed to do what I remember, except for the "tune". It picks something, I forget what, but seem to remember 90.5.
Also if I hook up an antenna, is there a way that I can see if a signal is getting in ? -
It's possible there can be current somewhere with it switched off, especially if it has a remote that can turn it on or stores preset stations in memory.
From what you describe now, I think the problem is probably in the 32V supply being high. If that voltage is too far out of spec it won't be able to lock on the frequency because the 32V rail is used to bias the varactor diode which is the active element in selecting the frequency. As I recall, this voltage is regulated by a classic linear regulator circuit with a zener diode reference. -
Getting closer.
The AM side works and I have noise coming out of the speakers. Now for the FM.
It seems like the FM signal will share the same amplifier circuit as the AM, at least I hope so.
I am trying to solve the FM problem in the same way that I did the AM.
I injected a 1khz test tone into the circuit at where I thought it would do some good, and followed it until it got to the speakers.
So, I was trying to find a source of a 88mhz signal for injecting into the FM circuit. So far no luck.
From the pictures I just posted it seems like I should be able to trace the FM signal starting at pin 21 of chip LA1266.
Now some questions.
At pin 21 of LA1266, should I be able to see a FM signal on a scope ?
Where should I be able to see the beginning of the FM signal chain ?
LA1266 is the AM/FM tuner
LA3401 is this VCO Non-Adjusting PLL FM MPX
Stereo Demodulator with FM Accessories
and I mostly do not know what it does.
Thanks
-
So does the AM tuning tune the correct station corresponding to the frequency shown on the display? Are all of the power supply voltages correct now? That is the first thing to check before doing any other troubleshooting, if the voltages are wrong it won't work.
-
Thank you again all for the help. I am getting closer and think that I want to start another thread.
The voltages are correct, not blowing fuses, and I can tune an AM station and actually listen to it. FM is another critter though.
So, I am going to start another thread for the FM .
Bye and thanks again. -
you did not have to start another thread ...
-
Why would you start another thread?! That just makes it confusing.
-
The voltages are correct...
Including the 32V rail? What was wrong with it? -
If I remember correctly, it was too high, almost 40v. Also, I have given up on this for now.The voltages are correct...
Including the 32V rail? What was wrong with it? -
why not put a 100watt light bulb in series with the power cord to limit the current,bridge the fuse and see what component gets hot?