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 Post subject: Zenith Royal 500 7ZT40
PostPosted: Jun Mon 30, 2014 5:11 pm 
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Joined: May Fri 23, 2014 5:56 pm
Posts: 48
When I started on this radio it was totally dead. I had to do a lot of
solder connection cleaning and repair. I also replaced the cap's. Now
here come's the the problem. When I turn it on, I receive local station's
accompanied by a loud squeal.I have the same problem with a royal 50
I did the cap's on.Any idea's on what may be causing the problem.
Thanks Roger


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 Post subject: Re: Zenith Royal 500 7ZT40
PostPosted: Jul Tue 01, 2014 4:02 pm 
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Joined: May Fri 23, 2014 5:56 pm
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HELP
This radio was pretty much a basket case when I got it.One problem I just noticed
there is a capacitor missing on under side of the chassis. What I need is someone
to post a picture of the location of that capacitor and where it solders to the chassis.
I also don't know what size the capacitor is.Any help would be certainly appreciated.
Thanks Roger


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 Post subject: Re: Zenith Royal 500 7ZT40
PostPosted: Jul Tue 01, 2014 8:26 pm 
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Location: Utica, NY 13502 (USA)
For reference, here is the schematic for the 7ZT40 chassis.

Attachment:
Zenith Royal 500 Ch 7ZT40 Sch.JPG
Zenith Royal 500 Ch 7ZT40 Sch.JPG [ 61.42 KiB | Viewed 4736 times ]


I suspect the missing cap could be the cause of the squeal. Sorry I can't help with a picture.

Dave


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 Post subject: Re: Zenith Royal 500 7ZT40
PostPosted: Jul Tue 01, 2014 11:08 pm 
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Posts: 4351
Location: Richmond, VA
Here is a photo of mine after a recap.

Attachment:
500capBot.jpg
500capBot.jpg [ 131.73 KiB | Viewed 4725 times ]


From left to right, I used a 47uF to replace the oem 50uF. Next is a 3uF which I replaced with a 3.3uF. It connects to the wiper of the volume control on the other side of the chassis. Last, at right, is either a 16uF on early models or a 3uF on later models. Mine was a 3uF so I used another 3.3uF.

I have also shown the positive ends of the caps. Hope this helps.

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 Post subject: Re: Zenith Royal 500 7ZT40
PostPosted: Jul Tue 01, 2014 11:47 pm 
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Ed -The schematic shows two (2) 50 uf caps. I only can see one (the 47 uf) in your picture. Is the 2nd cap on top of the chassis?

Dave


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 Post subject: Re: Zenith Royal 500 7ZT40
PostPosted: Jul Tue 01, 2014 11:52 pm 
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The other 50 uF is on top, next to the VC.

Image

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 Post subject: Re: Zenith Royal 500 7ZT40
PostPosted: Jul Wed 02, 2014 1:26 am 
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Sorry, I didn't post a picture of the top as Roger asked for a photo of the bottom of the chassis.

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 Post subject: Re: Zenith Royal 500 7ZT40
PostPosted: Jul Wed 02, 2014 4:38 pm 
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Good Morning From Phx.
Today will be another Ho Hum 112 degree's and I don,t have a pool. I wanted to say thanks
to Dave for the schematic it helped to identify the capacitors. The picture that Ed sent correct
me if I'm wrong is of a hand wired 7XT40 . The 7ZT40 I have has a printed circuit board, and on
the under side has two capacitors.That's the picture I was looking for.One of the cap's is wired
from the circuit board to the earphone jack, I'm not sure if I have that one wired in correct.The
other capacitor is the one that I don,t know where it connects and is soldered in.Please bare
with me this is only the fourth transistor radio I've ever worked on. I just enjoy bringing life back
to these old Radio's
Thanks Roger


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 Post subject: Re: Zenith Royal 500 7ZT40
PostPosted: Jul Wed 02, 2014 5:26 pm 
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Sorry, I wasn't paying attention. I've got a 7ZT40Z1, it should be the same except for transistor brand. I will pull the chassis and post a photo.

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 Post subject: Re: Zenith Royal 500 7ZT40
PostPosted: Jul Wed 02, 2014 6:22 pm 
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Roger, here are some photos of the bottom of the 7ZT40Z1 chassis after a recap. Both the caps on the bottom were originally 50uF caps. I used 47uF caps. For the cap that connects to the earphone plug, use an axial. For the other cap, a radial lead cap works best, but either kind can be used.

Attachment:
500Bcap1.jpg
500Bcap1.jpg [ 154.05 KiB | Viewed 4692 times ]


Attachment:
500Bcap2.jpg
500Bcap2.jpg [ 139.47 KiB | Viewed 4692 times ]


Attachment:
500Bcap3.jpg
500Bcap3.jpg [ 161.13 KiB | Viewed 4692 times ]

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 Post subject: Re: Zenith Royal 500 7ZT40
PostPosted: Jul Wed 02, 2014 7:13 pm 
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Location: Sunnyvale CA
Ed Morris wrote:
Roger, here are some photos of the bottom of the 7ZT40Z1 chassis after a recap. Both the caps on the bottom were originally 50uF caps. I used 47uF caps. For the cap that connects to the earphone plug, use an axial. For the other cap, a radial lead cap works best, but either kind can be used.


These pictures are great! Did you redo all the soldering on this one? All of my Zeniths from that era are much gloppier and grainy than these. I see a couple were there are only partial fillets but overall they look WAY better than any of mine.

Brett


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 Post subject: Re: Zenith Royal 500 7ZT40
PostPosted: Jul Wed 02, 2014 7:39 pm 
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Joined: May Fri 23, 2014 5:56 pm
Posts: 48
Ed
Thanks for the pictures they were exactly what I was looking for.You mentioned axial/radial
caps. Does this mean axial wire out both ends verses radial wires out the same end. Go
easy on me remember I'm new here.Now that I've got the info I need I'm going to finish
putting the 7ZT40 together I'll keep you posted on what happens.One more thing I just
purchased a non working ZXT40 I guess I'm a glutton for punishment.Just saying thanks again
for those pictures.
Thanks Roger


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 Post subject: Re: Zenith Royal 500 7ZT40
PostPosted: Jul Wed 02, 2014 7:57 pm 
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Brett, I may have touched up just a couple joints or iffy traces, but it is mostly as I got it.

Roger, yes the axial leads come out both ends of the capacitor. Radial leads come out the same end. With axial leads, the negative lead is usually pretty well marked, but radial leads can be a little tricker as different brands use different methods of identifying the negative lead.

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 Post subject: Re: Zenith Royal 500 7ZT40
PostPosted: Jul Wed 02, 2014 10:25 pm 
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Ed Morris wrote:
With axial leads, the negative lead is usually pretty well marked,

Actually I go by the "pinch" around the circumference on the positive side, although the arrows pointing to the negative end are also good indicators.
Ed Morris wrote:
but radial leads can be a little tricker as different brands use different methods of identifying the negative lead.

The universal ID for radial leads is that the positive is longer than the negative.

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 Post subject: Re: Zenith Royal 500 7ZT40
PostPosted: Jul Wed 02, 2014 10:59 pm 
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Thanks for the tip on the leads, Fifties. I didn't know about the difference in the leads.

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 Post subject: Re: Zenith Royal 500 7ZT40
PostPosted: Jul Thu 03, 2014 4:06 am 
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Joined: May Fri 23, 2014 5:56 pm
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Hey guys
I finished repairing my mistakes installed the caps correctly.I now have great volume
but only pickup two local stations.The two stations are loud and clear the rest are very faint.
I live in Phx AZ. so there's a lot of am stations. I have a little royal 50 that brings in all of
the local stations loud and clear no problem. Is this weak reception normal for the 7ZT40
Thanks Roger


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 Post subject: Re: Zenith Royal 500 7ZT40
PostPosted: Jul Thu 03, 2014 4:25 am 
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The eight transistor models are better than the early 7 transistor models, but I would think your 7ZT40 would pick up all your local stations, and even more distant stations at night.

Some of the more knowledgeable guys here should have some suggestions on what to look for.

Glad to hear you got your audio section working well.

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 Post subject: Re: Zenith Royal 500 7ZT40
PostPosted: Jul Thu 03, 2014 4:42 am 
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Rgr T Dgr wrote:
Is this weak reception normal for the 7ZT40
Thanks Roger


Definitely not. They certainly aren't as hot as a the types with RF amps (500D and subsequent), but there should be no problem at all getting many stations. I would suggest an alignment, or at least tweak the antenna trimmer. This is pretty safe to do and hard to mess up very much, and can make a huge difference. Tune it to a weak station around 1400 and slowly tune the antenna trimmer cap to max out the volume.

Other possibilities are the IF alignment, or a bad transistor in the RF/IF.

Brett


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 Post subject: Re: Zenith Royal 500 7ZT40
PostPosted: Feb Sat 21, 2015 6:57 pm 
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Please orientation of the four batteries. thx


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 Post subject: Re: Zenith Royal 500 7ZT40
PostPosted: Feb Sat 21, 2015 8:14 pm 
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henrypal wrote:
Please orientation of the four batteries. thx


See the photo in Fifties' first post in this thread, above. The four AA cells all go with the positive end pointing up, or toward the PC board, not the bottom of the radio.

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