Somebody give me a little nudge? Philco with no video

[AlanInSitges]

Thanks for that Tom.

I've been round and round with this a few different ways, with a scope probe, with a coupling capacitor, disconnecting the IF cable from the tuner, and just get no sign of anything.

I decided to take a working set and try the generator on that to narrow down the problem. I'm using a solid-state Sony TV-110. Feeding an RF signal from the Philips generator (a UHF channel 26 aprox), I can tune it on the Sony no problem, so I know the generator's RF output is working.

I've followed the instructions, such as they are, in the Philips manual, for injecting IF, which says to connect the RF lead, without matching transformer, through an isolating capacitor, to the input of the first IF stage, and tune the RF output to the receiver's intermediate frequency, which in this case is 38.9MHz. For reference:



Connecting the Philips generator's RF output to the Sony's IF input, I get no sign of anything on the screen except for some faint snow. Now, I know this IF input is working because I can put the tuner back on it and it works as expected. I have tried using a scope probe on X1 and X10 in place of the generator's RF lead, I have put a couple of different values of capacitor (68nf, .1mf) in series with the input, and sweeping from the bottom of the generator's range way up to the top, there is absolutely no sign of any signal - this is the same behavior on the Philco set that is the subject of this thread.

The generator has two low-band (which include IF) presets, a high-band preset, and two UHF presets. I've tried on both of these low-band presets with the same non-results. The UHF preset, as mentioned before, works as expected.

It is looking to me like maybe the generator isn't working on the low band. Is there another way I'm not thinking of to verify its operation (my scope only goes to 20MHz)? It sucks not being able to trust your tools.

If I'm unable to to verify that the generator is working correctly, I'm thinking about trying to patch the tuner IF output from the Sony to the Philco's IF input. Is there anything I need to keep in mind about that approach? Just strip the ends off of some coax and go to town?

Thanks again to everyone who's been helpful here.

[Electronic M]

Originally Posted by AlanInSitges

Thanks for that Tom.

It is looking to me like maybe the generator isn't working on the low band. Is there another way I'm not thinking of to verify its operation (my scope only goes to 20MHz)? It sucks not being able to trust your tools.

If I'm unable to to verify that the generator is working correctly, I'm thinking about trying to patch the tuner IF output from the Sony to the Philco's IF input. Is there anything I need to keep in mind about that approach? Just strip the ends off of some coax and go to town?

Thanks again to everyone who's been helpful here.

No problem.

If you supply a higher freq carrier than designed into your scope you can still glean some info. You won't be able to see individual cycles of the carrier wave or measure it's frequency (unless you have a digital frequency counter built into your scope), but you will be able to see it as a nice fat trace...The thickness of which will be modulated by the AM video carrier. You can check carrier presence, amplitude and modulation.

May want to clean the switches that control the output mode/frequency...Old push buttons can get tarnished contacts that won't work in some positions till cleaned.

Things to be aware of in tuner patch overs: If one set is hot chassis or has the chassis at some DC potential connecting the sets together could cause damage if you don't connect one and only one set to a line isolation transformer. Also, many sets especially tube era sets instead of having a discrete B- lead on the tuner instead used the shield on the IF coax as the DC return path for the B+...If you unhook the IF lead the tuner may loose power (unless you clip the IF shield to it). Lastly, if the set with the good tuner has its IF disconnected it will have no signal and may react to that by setting the tuner AGC line to a less than ideal value.....If you can navagate those pitfalls then using another sets tuner as an IF source is possible.