05-06-2025, 08:09 PM
Hi CGL18,
Here is a link for the schematic from the Early television Foundation:
https://earlytelevision.org/pdf/philco_g..._439-1.pdf
WARNING!! One side of the Chassis is directly connected to the AC Line! Fortunately, it is not the switched side. Please ensure that when connecting to house power that the Chassis is at neutral potential by measuring between the chassis and earth ground!
Avoid all temptation to adjust any slugs in the video or sound IF.
Slowly turn the tuner and "rock" the station selector back and forth. A lot of noise in picture and sound indicates possible poor contacts in the tuner, enough that no signal is provided.
Analyzing the schematic, there are several levels of B+. The 140V B+ is responsible for Video and Sound IF, and the Sound (quadrature) Detector. The 140V supply also supplies the screen of the Video Output tube, and the cathode of the Audio Output tube. However, the 140V supply is not used for the CRT, the Horizontal or Vertical sweep circuits, or the damper and no circuit fed by 140V is responsible for raster on the CRT. Therefore, this is the first place to check because if this supply is dead, it will cause exactly the problem that you describe. If this supply is good, the next step is to confirm B+ to the tuner and working forward, to the plate and screen of every tube in the Video and Audio IF sections.
The signal for the Sound IF comes from the Video Detector, so a bad diode section of the 5AM8 will cause the issue.
If the plate and screen voltages are good, check the capacitors that couple each stage and check all coils. the primaries are likely good or you will not have B+ at the plate. If a secondary of an IF or video coil is open, the signal will be blocked. Leaky caps will cause saturation of a tube (and possible red-plating).
Hope this helps.
Here is a link for the schematic from the Early television Foundation:
https://earlytelevision.org/pdf/philco_g..._439-1.pdf
WARNING!! One side of the Chassis is directly connected to the AC Line! Fortunately, it is not the switched side. Please ensure that when connecting to house power that the Chassis is at neutral potential by measuring between the chassis and earth ground!
Avoid all temptation to adjust any slugs in the video or sound IF.
Slowly turn the tuner and "rock" the station selector back and forth. A lot of noise in picture and sound indicates possible poor contacts in the tuner, enough that no signal is provided.
Analyzing the schematic, there are several levels of B+. The 140V B+ is responsible for Video and Sound IF, and the Sound (quadrature) Detector. The 140V supply also supplies the screen of the Video Output tube, and the cathode of the Audio Output tube. However, the 140V supply is not used for the CRT, the Horizontal or Vertical sweep circuits, or the damper and no circuit fed by 140V is responsible for raster on the CRT. Therefore, this is the first place to check because if this supply is dead, it will cause exactly the problem that you describe. If this supply is good, the next step is to confirm B+ to the tuner and working forward, to the plate and screen of every tube in the Video and Audio IF sections.
The signal for the Sound IF comes from the Video Detector, so a bad diode section of the 5AM8 will cause the issue.
If the plate and screen voltages are good, check the capacitors that couple each stage and check all coils. the primaries are likely good or you will not have B+ at the plate. If a secondary of an IF or video coil is open, the signal will be blocked. Leaky caps will cause saturation of a tube (and possible red-plating).
Hope this helps.
"Do Justly, love Mercy and walk humbly with your God"- Micah 6:8
"Let us begin to do good"- St. Francis
Best Regards,
MrFixr55
![[-]](https://philcoradio.com/phorum/images/bootbb/collapse.png "[-]")
