Help with schematic - Printable Version
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+- The PHILCO Phorum (https://philcoradio.com/phorum)
+-- Forum: Various and Sundry Categories (https://philcoradio.com/phorum/forumdisplay.php?fid=37)
+--- Forum: Test Equipment (https://philcoradio.com/phorum/forumdisplay.php?fid=31)
+--- Thread: Help with schematic (/showthread.php?tid=25545)
Help with schematic - Martinj - 01-10-2025
Having trouble reading this schematic. EMC 300 meter and the ac does not work.
RE: Help with schematic - DaleHCook - 01-11-2025
What part are you having trouble reading?
RE: Help with schematic - Martinj - 01-11-2025
The dc+ is void for 3v scale. Thats what thru me off. Also you need the batteries for the ac operation.
AC is perfect....
1. DC+ is off, 2.9vdc may measure 5vdc but its off on a curve so 4vdc goes full scale on 10v scale
2. DC- is backwards. Meter sets ok or full right but on negative voltage it tries to keep going right vs coming back down. Switching the leeds , the measurement is off.
3. Ohms wont go to standing full scale. There is no ohms adjust just zero adjust and it does nothing.
RE: Help with schematic - DaleHCook - 01-11-2025
Have you checked the 117L7 tube with a quality tube tester? Do you have a known good 117L7 that you can substitute? Have you looked at the chassis for signs of repairs which may have been done incorrectly? Have you replaced the wax-paper and electrolytic capacitors?
RE: Help with schematic - GarySP - 01-11-2025
All good spots to start with. I would include cleaning all contact switches with the proper DeOxit. Start with the easy and inexpensive and move up as needs require. Take care and BE HEALTHY! Gary
RE: Help with schematic - Martinj - 01-16-2025
Cleaned the switches and replaced a broken 9ohm resistor. Dc+ volts still pegs meter full left. 117l7 is perfect. Since this meter does not have bridge circuit, what balances out the meter?
RE: Help with schematic - Martinj - 01-17-2025
I tried to trace the dc+ but got lost.
RE: Help with schematic - Martinj - 01-23-2025
I tried disconnecting the lines at these points and while the meter does not peg left, it does not read voltages correctly. I added some pots to add resistance in the line to the meter, no luck