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 Post subject: Re: Zenith Z940 repair
PostPosted: Apr Fri 30, 2021 1:01 am 
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Posts: 16676
Location: Mountains of Mourne. Ireland.
Random image.
Image

That Littelfuse ←correct spelling) part number is ~50 years old, and I have no specification sheet. lol


Many glass fuses come it two flavors.
Look closely for markings to determine if it is F fast-blow or T slow-blow.
T (time) marking on the barrel indicates slow-blow.

NB: The fuse V rating is the maximum voltage, not the operating voltage.


Common size today is 6X30MM
Shop around for a good price.

Clean and gently squeeze the fuse posts if they are too loose.
If I'm not mistaken, Littelfuse N types are/was Slow Blow / Time Delay.

A quick parametric search at DigiKey shows these...
clear search filters to backtrack.

https://www.digikey.com/en/products/fil ... &sf=1&sv=0


Attachments:
Picture 19.png
Picture 19.png [ 81.74 KiB | Viewed 138 times ]
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 Post subject: Re: Zenith Z940 repair
PostPosted: Apr Fri 30, 2021 1:06 am 
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Joined: Dec Mon 28, 2020 11:52 pm
Posts: 165
Location: Davenport, Iowa
lorenz200w wrote:
pioneer07 wrote:


...I made the assumption that I could connect my new capacitors to these metal posts. I aligned the positive side with the symbol underneath (triangle, square or semicircle) and the negative side to the post with no symbol next to it. Was that an incorrect assumption?


Yes, bad assumption. The negative common connection is not brought out to any of the metal posts- it is connected to the aluminum can. It is impractical to solder to aluminum. That's why I suggested installing the new caps under the chassis using the old cap's terminals as tie points. You will have access to the old cap's negative terminal solder connection that way.

Lack of a symbol is a symbol itself. But it is just the positive terminal of another section of the multicap.


Thanks. Looks like I have some more work to do.


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 Post subject: Re: Zenith Z940 repair
PostPosted: Apr Fri 30, 2021 1:12 am 
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Joined: Dec Mon 28, 2020 11:52 pm
Posts: 165
Location: Davenport, Iowa
I would just prefer to have these caps in the space of where the old caps were, because there just isn't much room to work with on the underside. Lots of room above though.


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 Post subject: Re: Zenith Z940 repair
PostPosted: Apr Fri 30, 2021 1:28 am 
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Joined: Jan Tue 31, 2012 1:55 am
Posts: 16676
Location: Mountains of Mourne. Ireland.
This link on page one should show you all that you need to know about replacing filter capacitors.
Image
If and when I restuff a can, I drill a 3/16" hole in the center of the base and bring the insulated wires through / into the chassis and disregard the old solder tabs.

Insulate all leads inside the can.
and... if you've got OCD, you can line the inside of the can with a washed piece of plastic cut from a plastic "bottle"
HDPE – high density polyethylene. lol

Greg.


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 Post subject: Re: Zenith Z940 repair
PostPosted: Apr Fri 30, 2021 1:55 am 
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Joined: Dec Mon 28, 2020 11:52 pm
Posts: 165
Location: Davenport, Iowa
egg wrote:
Random image.
Image

That Littelfuse ←correct spelling) part number is ~50 years old, and I have no specification sheet. lol


Many glass fuses come it two flavors.
Look closely for markings to determine if it is F fast-blow or T slow-blow.
T (time) marking on the barrel indicates slow-blow.

NB: The fuse V rating is the maximum voltage, not the operating voltage.


Common size today is 6X30MM
Shop around for a good price.

Clean and gently squeeze the fuse posts if they are too loose.
If I'm not mistaken, Littelfuse N types are/was Slow Blow / Time Delay.

A quick parametric search at DigiKey shows these...
clear search filters to backtrack.

https://www.digikey.com/en/products/fil ... &sf=1&sv=0



Yes that image is what I've got. I'm very aware the 6x30 is a common size. That won't fit in this fuse holder though, I mean it might but it's unclear how it would latch (the little nubs that stick out are what hold this one in place in the current fuse holder). So I'd have to also replace the fuse holder to go to a 6x30 fuse. I guess it may not be a bad idea to mordernize the fuse and holder though.


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 Post subject: Re: Zenith Z940 repair
PostPosted: Apr Fri 30, 2021 2:11 am 
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Posts: 256
Location: Saint Paul, Minn
What I have done is to remove that old fuse holder and put in standard 1/4x1-1/4 fuse style. I've done it to two chassis and it works just great and the fuses are available. One of the reasons I did this is when working on the chassis out of the cabinet I rubbed against the top of the fuse and the chassis - it only took ONE time if you get my drift. In order to fit the chassis , the hole has to be enlarged just s little bit, I used a step drill bit and it worked fine.

Those are type "N" fuses if I remember correctly.


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 Post subject: Re: Zenith Z940 repair
PostPosted: Apr Fri 30, 2021 2:15 am 
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Joined: Dec Mon 28, 2020 11:52 pm
Posts: 165
Location: Davenport, Iowa
lorenz200w wrote:
pioneer07 wrote:


...I made the assumption that I could connect my new capacitors to these metal posts. I aligned the positive side with the symbol underneath (triangle, square or semicircle) and the negative side to the post with no symbol next to it. Was that an incorrect assumption?


Yes, bad assumption. The negative common connection is not brought out to any of the metal posts- it is connected to the aluminum can. It is impractical to solder to aluminum. That's why I suggested installing the new caps under the chassis using the old cap's terminals as tie points. You will have access to the old cap's negative terminal solder connection that way.

Lack of a symbol is a symbol itself. But it is just the positive terminal of another section of the multicap.

IF somehow you managed to connect one of the caps such that the negative lead was at a higher DC potential than the positive lead, that cap is very likely ruined. Don't try to re-use it by correctly connecting it.



This is the underside of the C1 capacitor, which is just a single cap with 2 prongs. The positive side is the post with the square symbol, and I have to believe the post with no symbol has to be the negative side, since it is the only other thing with any wires connected to it. I see those 4 prongs around the outside you were referring to, but those are not being used (you can see 2 of them in this photo, you'll have to take my word for it on the other 2). The red/yellow striped insulated wire and then the green/yellow striped wire you see soldered to these posts come straight out of the transformer.

Attachment:
C1_1.JPG
C1_1.JPG [ 204.39 KiB | Viewed 132 times ]


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 Post subject: Re: Zenith Z940 repair
PostPosted: Apr Fri 30, 2021 2:21 am 
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Joined: Dec Mon 28, 2020 11:52 pm
Posts: 165
Location: Davenport, Iowa
egg wrote:
This link on page one should show you all that you need to know about replacing filter capacitors.
Image
If and when I restuff a can, I drill a 3/16" hole in the center of the base and bring the insulated wires through / into the chassis and disregard the old solder tabs.

Insulate all leads inside the can.
and... if you've got OCD, you can line the inside of the can with a washed piece of plastic cut from a plastic "bottle"
HDPE – high density polyethylene. lol

Greg.



I went down that rabbit hole on page 1 but it kept getting deeper and deeper. Someday when I have a lot more time I'll have to actually read all those threads that link to other threads...that link to other threads. I did skim some of them and I saw one image that looked kinda like what I have. Bookmarked that one.


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 Post subject: Re: Zenith Z940 repair
PostPosted: Apr Fri 30, 2021 2:27 am 
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Joined: Dec Mon 28, 2020 11:52 pm
Posts: 165
Location: Davenport, Iowa
SeniorSteve wrote:
What I have done is to remove that old fuse holder and put in standard 1/4x1-1/4 fuse style. I've done it to two chassis and it works just great and the fuses are available. One of the reasons I did this is when working on the chassis out of the cabinet I rubbed against the top of the fuse and the chassis - it only took ONE time if you get my drift. In order to fit the chassis , the hole has to be enlarged just s little bit, I used a step drill bit and it worked fine.

Those are type "N" fuses if I remember correctly.



I actually found a 5 pack of the exact fuses this takes on Ebay for $5 plus shipping. I'm going to go with these for now, but yeah, at some point I may do what you are describing. It will just make it a lot easier to find fuses for this in the future. Yes, these are "N" fuses.


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 Post subject: Re: Zenith Z940 repair
PostPosted: May Tue 04, 2021 3:55 pm 
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Joined: Dec Mon 28, 2020 11:52 pm
Posts: 165
Location: Davenport, Iowa
I drilled a hole in the bottom of those aluminum can capacitors and ran insulated wires to the solder joints as suggested. I replaced the C1, C2A, C2B, and C2C capacitors, connecting the positive side to the terminals with the square, semicircle or triangle symbol. I connected the negative side to the terminal with no symbol. This seems to be the correct way judging by the schematic. But I just tested it and blew the fuse again. I did also replace the fuse + holder with a more modern 6x30 equivalent, so it will be easier to get more if I keep blowing them.

Here is the power circuit. The capacitors I've changed are on the right but I have not replaced C3 yet. I'm looking for suggestions on how to troubleshoot this. Thanks

Attachment:
Power.JPG
Power.JPG [ 261 KiB | Viewed 106 times ]


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 Post subject: Re: Zenith Z940 repair
PostPosted: May Tue 04, 2021 4:25 pm 
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Joined: Feb Tue 02, 2016 2:38 am
Posts: 256
Location: Saint Paul, Minn
If I read your description correct, you tied all of the capacitor's negative leads together. You have them backwards, as this is a positive chassis ground set. I hope you haven't turned it on yet (oops I see you have), as it is going to blow the fuse and most likely damage the newly installed capacitors -C1 for sure will be compromised as it is the first filter.

I don't think anything else would be damaged as the filter is almost a short when wired backwards.

Steve


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 Post subject: Re: Zenith Z940 repair
PostPosted: May Tue 04, 2021 4:39 pm 
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Joined: Dec Mon 28, 2020 11:52 pm
Posts: 165
Location: Davenport, Iowa
SeniorSteve wrote:
If I read your description correct, you tied all of the capacitor's negative leads together. You have them backwards, as this is a positive chassis ground set. I hope you haven't turned it on yet (oops I see you have), as it is going to blow the fuse and most likely damage the newly installed capacitors -C1 for sure will be compromised as it is the first filter.

I don't think anything else would be damaged as the filter is almost a short when wired backwards.

Steve



Ooof. This seems to contradict this comment on page 1 of this thread, where they said the terminals with the symbols were the positive leads:
viewtopic.php?p=3370976#p3370976

I want to be absolutely sure you're right before I do this.

I have another question. Another previous comment said that I needed to tie into the 4 prongs around the outside of these aluminum cans. When I got this unit, there are no wires going to those at all. I'm wondering: maybe there was an internal connection that I broke when I sawed off these capacitors? And since I broke that connection, perhaps I DO need a wire to tie into those outside prongs now? It would go from whichever side of the cap is supposed to be ground to one of these outside prongs.


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 Post subject: Re: Zenith Z940 repair
PostPosted: May Tue 04, 2021 5:17 pm 
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Joined: Feb Tue 02, 2016 2:38 am
Posts: 256
Location: Saint Paul, Minn
It could be possible that the unmarked terminal is the common positive terminal, does that terminal have a wire that connects to the chassis? That would have to be a can with 3 capacitors and the unmarked as the common. If so, you have your answer. That would also make sense why the mounting ring tabs didn't have any connections to them. I'm sure you didn't saw off any connection. If there wasn't any connection, the fuse wouldn't have blown. If you look at the schematic you will see little "+" marks on the connection that goes to ground (chassis).

Hope this clarifies you question,
Steve


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 Post subject: Re: Zenith Z940 repair
PostPosted: May Tue 04, 2021 5:31 pm 
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Joined: Dec Mon 28, 2020 11:52 pm
Posts: 165
Location: Davenport, Iowa
SeniorSteve wrote:
It could be possible that the unmarked terminal is the common positive terminal, does that terminal have a wire that connects to the chassis? That would have to be a can with 3 capacitors and the unmarked as the common. If so, you have your answer. That would also make sense why the mounting ring tabs didn't have any connections to them. I'm sure you didn't saw off any connection. If there wasn't any connection, the fuse wouldn't have blown. If you look at the schematic you will see little "+" marks on the connection that goes to ground (chassis).

Hope this clarifies you question,
Steve



After giving this another look, I believe you are correct. The C3 cap has a black wire connected to the positive side that, through a couple point-to-point wires ultimately connects directly to the C2 cap with no resistors or anything in between. In other words: right now I have the positive side of C3 connected to the negative side of the C2 caps. Oops.

There is not a clear or easy way to tell where it is grounded. That's part of why I'm struggling here (along with the info on page 1). The two wires that connect to C1 both go into the transformer and disappear. But if you look at that schematic I posted, it does say there is a red/yellow wire that is supposed to go to the negative terminal of C1, and I have it going to the positive terminal. So yeah. That is a problem. Thanks. The other wire that goes to C1 appears to be green/yellow and I cannot see how that one is grounded, as I said. It must be grounded inside the transformer. I will replace these caps with new ones and flip them the right way and see what happens.


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 Post subject: Re: Zenith Z940 repair
PostPosted: May Tue 04, 2021 6:38 pm 
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Location: Saint Paul, Minn
I looked at the picture you posted of C1 under the chassis in an earlier post. It looks like the center tap of the transformer (red/yellow) is connected to the other terminal of that cap. If you look closely there is a wire going from the unmarked terminal of that cap (c1) to the chassis with a bare wire. That should be the positive side of the capacitor. C2 has 3 sections, but all of the positive sides are connected together. On the side of the cap you will see the values for each section, then a _ symbol and something like Com POS which means common positive. That common positive connections will also be connected to the chassis in some form. You will notice that all of the supply voltages show a - in front of them to signify they are a negative voltage with respect to the chassis. Many of those can caps did not use the outside can for a connection, that's why you won't see a connection to those mounting rings. Hope this helps.


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 Post subject: Re: Zenith Z940 repair
PostPosted: May Tue 04, 2021 8:26 pm 
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Joined: Dec Mon 28, 2020 11:52 pm
Posts: 165
Location: Davenport, Iowa
SeniorSteve wrote:
I looked at the picture you posted of C1 under the chassis in an earlier post. It looks like the center tap of the transformer (red/yellow) is connected to the other terminal of that cap. If you look closely there is a wire going from the unmarked terminal of that cap (c1) to the chassis with a bare wire. That should be the positive side of the capacitor. C2 has 3 sections, but all of the positive sides are connected together. On the side of the cap you will see the values for each section, then a _ symbol and something like Com POS which means common positive. That common positive connections will also be connected to the chassis in some form. You will notice that all of the supply voltages show a - in front of them to signify they are a negative voltage with respect to the chassis. Many of those can caps did not use the outside can for a connection, that's why you won't see a connection to those mounting rings. Hope this helps.



Yes I finally spotted the chassis ground also for C1. I can see how the common positive side of the C2 capacitors connect to the positive terminal of the C3 capacitor. The C2 and C3 positive terminals do not go to the same chassis ground as C1 though. I think this is how they are grounded:

Attachment:
Capture.JPG
Capture.JPG [ 328.89 KiB | Viewed 83 times ]



Only problem is that I just tried it this way with all the positives grounded instead of the negatives...and blew the fuse again. Baffling.

Should I replace C3 before I go any further? Could C3 be shorted internally? That's the other big cap in this circuit I haven't replaced yet.


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 Post subject: Re: Zenith Z940 repair
PostPosted: May Tue 04, 2021 9:00 pm 
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If you have a meter, now would be the time to start checking what kind of resistance you get from the negative supplies to the chassis. If all you replaced was C3 and it shorted what you would have some severely overheated R139 and R140 resistors. Have you replaced C1 or C2 as well? If so, that would be the first place I would look as that will take the brunt of the current if it was installed backwards. Also You may want to check the power supply diodes X1 and X2 as the surge current may have caused one or both of them to short. You don't want to continue blowing fuses until you find out what is wrong. Blowing the fuse means there is a serious problem and you don't want to stress the transformer any more than you need to. To check the diodes you will need to lift one side of them before taking the resistance measurement. If you are using a digital meter, you will have to use the diode function because some of the meters don't have enough forward voltage to check them correctly.

Steve


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 Post subject: Re: Zenith Z940 repair
PostPosted: May Tue 04, 2021 9:11 pm 
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Joined: Dec Mon 28, 2020 11:52 pm
Posts: 165
Location: Davenport, Iowa
SeniorSteve wrote:
If you have a meter, now would be the time to start checking what kind of resistance you get from the negative supplies to the chassis. If all you replaced was C3 and it shorted what you would have some severely overheated R139 and R140 resistors. Have you replaced C1 or C2 as well? If so, that would be the first place I would look as that will take the brunt of the current if it was installed backwards. Also You may want to check the power supply diodes X1 and X2 as the surge current may have caused one or both of them to short. You don't want to continue blowing fuses until you find out what is wrong. Blowing the fuse means there is a serious problem and you don't want to stress the transformer any more than you need to. To check the diodes you will need to lift one side of them before taking the resistance measurement. If you are using a digital meter, you will have to use the diode function because some of the meters don't have enough forward voltage to check them correctly.

Steve



You are misunderstanding - I have replaced C1, C2A, C2B and C2C. I have NOT replaced C3 yet


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 Post subject: Re: Zenith Z940 repair
PostPosted: May Wed 05, 2021 12:22 am 
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I stand corrected, sorry. If that's the case, you probably need to replace C1 for sure as it took the brunt of the current when it was installed reverse polarity. I wouldn't do anything until C1 is replaced. At this point in time I don't believe C3 is part of the issue.

Steve


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 Post subject: Re: Zenith Z940 repair
PostPosted: May Wed 05, 2021 1:44 am 
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Joined: Dec Mon 28, 2020 11:52 pm
Posts: 165
Location: Davenport, Iowa
SeniorSteve wrote:
I stand corrected, sorry. If that's the case, you probably need to replace C1 for sure as it took the brunt of the current when it was installed reverse polarity. I wouldn't do anything until C1 is replaced. At this point in time I don't believe C3 is part of the issue.

Steve



Thanks for the help.

I replaced C1 in this last round, so I'm on replacement #2 of C1, and it still blew the fuse, even connected correctly with the positive side to ground.

No resistors look fried to me but who knows

I do not think the issue is with X1, X2, C110 or C111. They are the cluster at the top center of the image (2 caps and 2 gold cylinders). I have not touched that part of the circuit so it has been hooked up correctly this whole time. I guess if there is some secondary effect from me hooking up these others caps wrong, they could be damaged but I don't know. Seems slightly less likely to me but maybe I'm wrong.

What about X10? That one goes directly from the triangle terminal under C2, directly to the blank terminal under C2 (which is ground). So when I had these caps backwards, that diode would have essentially been hooked up backwards, too. Is it possible I fried that one? That one though is downstream of these other caps so not sure that would cause this issue.

Attachment:
X10.JPG
X10.JPG [ 332.43 KiB | Viewed 72 times ]


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