116X issues, burning up part #80 for meter - Printable Version
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+--- Thread: 116X issues, burning up part #80 for meter (/showthread.php?tid=21377)
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116X issues, burning up part #80 for meter - Lsparky59 - 05-31-2020
Gentlemen.
I have just gone through this receiver, 1936 model, and just for the record, I took pictures of every conceivable angle before I replaced any components. I restuffed the original bypass and coupling capacitors, swapped nearly all the resistors(only the ones that were bad by 20% or more) and replaced all the 'lytics.
This problem did not show up on the original dogbone (2K part # 80 on the schematic, it showed no signs of overheating. The only part that showed signs of overheating was the .3 uf capacitor that goes across the filter choke (101). Of course, this was swapped out. The only difference is that the schematic showed one .3 uf cap, while there was two .3 uf caps in the bakelite cover. I put two back in it. Production change?
When I first energized the chassis after rebuild, I did it slowly on a variac, and only did I noticed at around 90-100 V, that the resistor was slightly discolored and I could smell something cooking. I use 1 W flameproof resistors throughout the rebuild. I actually burnt several of these up trying to locate the cause of the problem.
Of course, I double check all my connections and work, comparing with the before pictures and no components are out of place. No shorts, no backward components.
I started back tracking by disconnecting all the wiring associated with the 2K resistor and shadowmeter. Starting on the B+ side and working my way back until I came to where the wires attach the longwave RF transformer. Both of the these go to the bandswitch wafer marked as #4 on the schematic. As you are looking at the chassis with the controls facing up, its the bottom two wires on the transformer that go to the bandswitch.
Jumping either one of the wires from the bandswitch back to the longwave transformer, results in cooking the shunt resistor. Another thing that I observed is as long as the bandswitch is in upper band (SW) there is no problems, so as you select the lower bands, the trouble starts.
I cleaned the bandswitch with Deoxit, thinking that maybe I had a carbon track causing the shorting issue, but that made no difference. While poking around the area I found a broken wire that goes from the bandswitch to the RF transformer (BC, SW and Police bands). It is quite confusing to know which terminal this would attach to and wondering if it may be the cause of the problem. I circled the wire on the attached schematic. I have also attached a pic showing the detached wire.
Something is making this shunt resistor draw excessive current and I can't quite put my finger on it. I'm usually pretty good figuring these out, since I do have an electrical background. But I'm just about ready to put the radio in the "land of misfit radios" (upstairs above my little hobby shop)
Thanks in advance for any help, tips, suggestions.
RE: 116X issues, burning up part #80 for meter - Radioroslyn - 05-31-2020
>It is quite confusing to know which terminal this would attach to and wondering if it may be the cause of the problem. I circled the wire on the attached schematic. I have also attached a pic showing the detached wire.
It could. The bottom of the coil is connected to the hv line thru #22 1K resistor. Other options are 23, and 47 (lower section). Something simple to do is measure the resistance from the chassis to each end of #22. The lower resistance determens which side of the resistor closer to the short. Measure w/the bs in the lower frequency position.
Happy Hunting!
RE: 116X issues, burning up part #80 for meter - Lsparky59 - 05-31-2020
Thanks, I'll give it a shot. Maybe someone with a really good picture or even the same radio where they can be kind enough to locate it for me as well. It's in a pretty obscured area.
RE: 116X issues, burning up part #80 for meter - Radioroslyn - 05-31-2020
I have a 116X chassis that is accessible to have a look at. Is there a way you can reference the position of your loose wire so I can figure out where on the coil it's connected?
RE: 116X issues, burning up part #80 for meter - Lsparky59 - 05-31-2020
I took this picture, hope it clarifies. If you look at the back of the chassis, with the controls and dial facing up, it is the forth bandswitch wafer from the top. If you count the terminals starting on the right side of the mounting posts for the wafers, the first two are tied together, the third wire down is red and the fourth wire down is the one that is disconnected from the RF coil. My test lead is pinting right at the wire in question. Thanks.
RE: 116X issues, burning up part #80 for meter - Lsparky59 - 05-31-2020
I already replaced the (new) .05 uf caps in 47 because I suspected they may have been the problem. I did this before I posted when I was still trying to figure it out. I haven't done 23 yet with the meter. Been a loooong day.
RE: 116X issues, burning up part #80 for meter - Ed Locker - 06-01-2020
I believe that the .3 bakelite block is really 2 .15's in parallel.
RE: 116X issues, burning up part #80 for meter - Lsparky59 - 06-01-2020
I believe you're right, but I don't think that would cause the issue I'm experiencing. I could be wrong.
RE: 116X issues, burning up part #80 for meter - Bill Bacco - 06-01-2020
If you haven't already done so, you might want to confirm the wiring on the rotary switch matches the schematic. It is possible that it was messed up prior to your repair. If I had the 116X schematic, I could possibly help troubleshoot the issue more.
RE: 116X issues, burning up part #80 for meter - Lsparky59 - 06-01-2020
I posted a reply. Dont know if you got it or not. I'm still a newb navigating my way around the phorum. Thanks in advance.
RE: 116X issues, burning up part #80 for meter - Lsparky59 - 06-01-2020
Except for a couple of electrolytics that were replaced, the chassis was untouched, it had the original Philco bypass, coupling capacitors, which I restuffed and had the original resistors, most which were out of tolerance and replaced. Except for the broken wire on the bandswitch to the RF coil for the BC. Police and SW bands. See my previous posts.
RE: 116X issues, burning up part #80 for meter - Radioroslyn - 06-01-2020
Sent over some pics of the 116X bandswitch via email as the Phorum limits file sizes. Hopefully this will be of some benefit.
RE: 116X issues, burning up part #80 for meter - Lsparky59 - 06-02-2020
It looks like that wire on terminal 4 on the 4th wafer goes to one of the bottom three terminals on the RF coil, but it's hard to tell from the picture.
RE: 116X issues, burning up part #80 for meter - Lsparky59 - 06-05-2020
It looks like that wire on terminal 4 on the 4th wafer goes to one of the bottom three terminals on the RF coil, but it's hard to tell from the picture. Any clarification to verify.
Thanks
RE: 116X issues, burning up part #80 for meter - Lsparky59 - 06-05-2020
It is the 4 wafer down from the front. The wire in question is on the terminal below the one with the red wire, it will be the forth terminal from the top ( the first two terminals are jumpered). I have put arrows on the picture you sent me to help clarify. For the life on me, the schematic is either wrong or there was a production change. Normally, I don't have any issues figuring it out, but this one is driving me crazy.
Thanks