A Zenith 8G005YT restore - Printable Version
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+--- Thread: A Zenith 8G005YT restore (/showthread.php?tid=14687)
RE: A Zenith 8G005YT restore - klondike98 - 07-20-2016
I swapped out two new 1LN5 tubes just to see if that might solve my problem...no it didn't. With the speaker connected I can still tune in the local AM station but only very faintly. It seemed that adjusting the volume control did not do much to change the volume...hmmm. I suppose I could see if I can find another 2nd IF transformer and swap that but that will likely mean finding a junker set to pull it from....grumble grumble...
I guess I need to find a signal tracer and see if I can find where I'm losing signal.
RE: A Zenith 8G005YT restore - Phlogiston - 07-20-2016
(07-20-2016, 06:38 PM)klondike98 Wrote: I swapped out two new 1LN5 tubes just to see if that might solve my problem...no it didn't. With the speaker connected I can still tune in the local AM station but only very faintly. It seemed that adjusting the volume control did not do much to change the volume...hmmm. I suppose I could see if I can find another 2nd IF transformer and swap that but that will likely mean finding a junker set to pull it from....grumble grumble...
I guess I need to find a signal tracer and see if I can find where I'm losing signal.
Though I seldom use mine, when you have a problem like yours, it may be very helpful.
You should be able to find one for $25 or so.
RE: A Zenith 8G005YT restore - klondike98 - 08-30-2016
Back to the Zenith… the schematic link is here (ignore the red highlighting).
I did get a signal tracer and here’s what’s going on:
Set signal generator RF at 1050 KC and turned modulation on.
Injected signal at the antenna and tuned the radio to 1050.
I can hear tone at the radio speaker but I have to turn the radio volume to full (this is the same as when I tune to the local AM station, I can hear it but only on full volume).
Signal tracer probe on antenna = I can hear the modulation tone through signal tracer speaker.
Signal tracer probe on grid (pin 6) of 1LN5 R.F. = I can hear the modulation tone.
Signal tracer probe on grid (pin 6) of 1LC6 Converter = slightly louder tone
Signal tracer probe on grid (pin 6) of 1LN5 I.F = louder tone
Signal tracer probe on grid (pin 6) of 1LD5 = very very faint tone
Signal tracer probe on Dp (pin 4) of 1LD5 = very very faint tone
Sounds to me like signal is getting lost in the 2nd IF transformer which is consistent with me not being able to get it to peak when trying to align it. Or is it possible its a bad 1LD5? I've switched out 1LN5s with no changes. Voltages are all good. So…I’m at the end of my troubleshooting skills. The coil shows continuity so perhaps one of the caps in it has failed? Unfortunately there are no values on any of them. Any suggestions for a next step? Try to find a replacement 2nd IF transformer. Thanks for any help on this one!!!
RE: A Zenith 8G005YT restore - Radioroslyn - 08-30-2016
one of the caps in it has failed?
Good chance!
I would pop the cover off of the IF transformer,chop out the two caps inside. Reinstall cover and solder replacement caps at the bottom terminals. You may have to experiment a bit to find the proper value but it's probably between 75-125mmf. I'd start with 100mmf and see if I can get a peak by adjusting the slugs. They say it's a virtue!!!
RE: A Zenith 8G005YT restore - klondike98 - 08-30-2016
I was afraid that might be next, unfortunately there are 4 caps in the 2nd IF transformer, one each across the primary and secondary and then 2 in the circuit just below the secondary but inside the transformer can....oh, and they are all buried in wax... this surgery could be interesting
RE: A Zenith 8G005YT restore - Radioroslyn - 08-30-2016
The two below the IF coils are not very critical two 220mmf will work fine, they filter rf out of the audio signal going to the volume control. The ones that are critical are the two across the coils, resonate the coils to the IF frequency.
RE: A Zenith 8G005YT restore - klondike98 - 08-31-2016
Thanks Terry!
RE: A Zenith 8G005YT restore - klondike98 - 09-10-2016
I did some surgery on the 2nd IF transformer. Took out the two caps across the transformer coils and replaced them with two 82 pF caps. Pic shows the first new cap in place and the one remaining old cap at the bottom. Buttoned it up again and ….. nada …. No signal at all coming through the 2nd IF transformer now. I was about to take it out and try some 100 pf caps when I thought about an observation I had made while signal tracing. I recalled getting signal at the output of the filter circuit in the 2nd IF can… probably shouldn’t be seeing that and decided to try disconnecting that at the point where the slate colored wire (SL) connects to the 1LD5 filament line. Heard signal now at the speaker!! So that filter circuit must have failed. I was able to align the 1st and 2nd IF transformers now although the only AM channels I can get are the local ones. I think this still needs more work but it will be the next guy will have to do it.
[Image: https://www.dropbox.com/s/sfwktjx8lb2u53a/zenith8G005_33.jpg?raw=1]
[Image: https://www.dropbox.com/s/sa6vk7cxk422dcf/zenith8G005_34.jpg?raw=1]
RE: A Zenith 8G005YT restore - klondike98 - 09-22-2016
[Image: https://www.dropbox.com/s/7x6ls4dtjlaojqb/touchdown.jpg?raw=1]
[Image: https://www.dropbox.com/s/xwwu2z1zd6icv68/8G005_schematic.jpg?raw=1]
I just didn't feel good about this set not working well and found a parts chassis at Ktown so I pulled it apart again. Its always in the details.... I was losing signal around the 2nd IF transformer and the reason was not the transformer but faulty recapping by the repair guy
. I had the 0.05 cap circled in green connected to pin 4 of the 1LD5 rather than the correct position of pin 3.... ack! I had already modified the 2nd IF transformer by swapping out caps and they were not the correct value. I was getting signal through but could not really peak it properly. Terry pointed out that I should probably have something closer to 100pf caps in there while I used 82s. Anyway, since I had already picked up the parts chassis I swapped out the 2nd IF transformer from it and the set aligned nicely and I'm getting all bands at nice volumes. Thank you to each of you who commented and helped along the way and especially thank you Terry (Radiorosyln)! I can now get this set back to its owner in decent shape.
RE: A Zenith 8G005YT restore - sam - 09-22-2016
Aww come on bob
buy a parts chassis cheater
Congrats on getting it working
And great Job terry
RE: A Zenith 8G005YT restore - Eliot Ness - 09-26-2016
Good job Bob
Sometimes having another chassis to compare comes in quite handy.
RE: A Zenith 8G005YT restore - Paul Philco322 - 10-10-2016
I understand these can be complex jobs but play like a dream when done over. Super Deluxe Bob.
Paul
RE: A Zenith 8G005YT restore - klondike98 - 10-10-2016
Thanks! This model is, I think, a bit less of a pain than later models but it did pull in a lot of stations when I finally got it going. I like it so much I've picked up another off ebay and will be working on it soon. With the parts set I have and the one that's coming I should be able to get it going.
RE: A Zenith 8G005YT restore - Radioroslyn - 10-10-2016
Please No no no I can't take it anymore!!!! Tubes,capacitors, transformers, signal here no signal there I'm going mad I tell you I
said madd!!!!!!
Have fun w/it
RE: A Zenith 8G005YT restore - KCMike - 10-10-2016
(10-10-2016, 07:42 PM)Radioroslyn Wrote: Please No no no I can't take it anymore!!!! Tubes,capacitors, transformers, signal here no signal there I'm going mad I tell you I
said madd!!!!!!
Have fun w/it
Terry you have been a great help to lot of people here.I wish I had a electrical problem to ask about. Pulling my hair out trying to get the mechanical problems with a Sears silvertone record changer figured out.
