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47-1230 Blown R315 1K Resistor - Printable Version

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47-1230 Blown R315 1K Resistor - Pepperoni - 04-23-2016

I recently performed a re-cap of this 47-1230. The radio has been working fine since. Then a couple months later, a puff of smoke and it died. A visual inspection revealed that the R315 1K resistor had fried. I have the paperwork from Chuck but I'm having trouble sizing it for posting here so I've added the link from NA to the schematic. Problem is in "Section 3" of the schematic.

http://www.nostalgiaair.org/pagesbymodel/606/M0013606.pdf

The problem appears to be on the Z302 IF side of the resistor. I isolated the red wire from Z302 and my resistor doesn't fry. I checked the resistances of Z302 and I may have an anomaly. Reading from the red wire to the blue wire I have 11 ohms. This matches the schematic. Orange wire to yellow wire is about 4 ohms.? But from the green wire to pin 4 of the 7R7 tube I see about 7.2 meg. This is way over the 10 ohms on the schematic. I hope I'm measuring the correct points. This 7.2 meg is seen across the green wire and the white wire which connects to pin 4 of the 7R7. White wire not labeled "White" on the schematic.

I believe my problem is inside the Z302 IF but I wanted another opinion before I open up that can. Am I going in the right direction with my troubleshooting?

Pepperoni

RE: 47-1230 Blown R315 1K Resistor - Radioroslyn - 04-23-2016

Hi John,
Well the obvious is shorted C317. Check the resistance from the plate to ground would think it should be more than 5K or so. Check for shorting connections or wires shorting from the recap.

Terry

RE: 47-1230 Blown R315 1K Resistor - Pepperoni - 04-23-2016

Appreciate it Terry. I opened up the Z302 IF can and found C302A, 27pf mica cap reading 88 ohms when isolated. Replaced that with a 25pf silver mica and the radio lives again. I guess that cap just got tired.

Thanks again,
John

RE: 47-1230 Blown R315 1K Resistor - Radioroslyn - 04-23-2016

(04-23-2016, 04:30 PM)Pepperoni Wrote:  Appreciate it Terry. I opened up the Z302 IF can and found C302A, 27pf mica cap reading 88 ohms when isolated. Replaced that with a 25pf silver mica and the radio lives again. I guess that cap just got tired.

Thanks again,
John

I saw that cap but it looked like it has some fairly high resistor hooked to it so was thinking that if it did short that it would load the B+ that much. I hate those newer Philco diagrams where there all split up!
Good Job!!

Terry