Bridge rectifier putting out approx 170VDC?


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Bridge rectifier putting out approx 170VDC?

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ajcrm125
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Mar 15, 2012, 3:44 PM

Post #1 of 32 (4753 views)
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Bridge rectifier putting out approx 170VDC?	Can't Post

Workin on my 32" Zenith GX chassis what wil shutdown immediately after turning on. I thought it might be the HV shutdown circuit so I started measuring what voltages I could while the TV was plugged in, but powered off. I noticed that the +150DC coming out of the bridge rectifier was +167VDC. Is this high enough to cause other problems?

And I guess a secondary question would be.. how can 120VAC produce 167VDC through the bridge? Shouldn't the most this thing should be able to produce be +120VDC? What am I missing?

Here's the schematic. I circled the section in question.
http://www.onecircuit.com/sites/onecircuit.com/files/temp/hv.jpg-Adam
==================
http://www.onecircuit.com
==================

Ron.M
Veteran

Mar 15, 2012, 8:12 PM

Post #2 of 32 (4747 views)
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Re: [ajcrm125] Bridge rectifier putting out approx 170VDC? [In reply to]	Can't Post

ajcrm125;.....

That IS a normal voltage coming from that type of bridge circuit...
When you take full-wave rectification & filter it you get a "bonus" voltage..
NOT a technical explanation , but , you get the point...
The +167 vdc is a "no-load" reading...
Instant shutdown indicates a different problem...
Please post a model number so I can possibly of more help...
THANKS... Sly

....

Later...Ron.M... Cool

...
Veteran & Retired TV technician

ajcrm125
New User

Mar 15, 2012, 8:23 PM

Post #3 of 32 (4744 views)
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Re: [Ron.M] Bridge rectifier putting out approx 170VDC? [In reply to]	Can't Post

Thanks for the explanation Ron. The TV is a 32" Sony model # SY3572DT.

Thanks!
-Adam
==================
http://www.onecircuit.com
==================

Ron.M
Veteran

Mar 15, 2012, 8:49 PM

Post #4 of 32 (4741 views)
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Re: [ajcrm125] Bridge rectifier putting out approx 170VDC? [In reply to]	Can't Post

ajcrm125;....

According to the model number , it's 35" , not a 32....
NO big deal....
Also according to the model number it's a "ZENITH" NOT a "SONY" !!!!
Could've been a big deal... Crazy

...
Give me some time to get a service manual...
Unless you have a link to yours...

How much electronic/TV repair background experience do you have ????

Later...Ron.M.... Cool

...
Veteran & Retired TV technician

ajcrm125
New User

Mar 15, 2012, 9:55 PM

Post #5 of 32 (4728 views)
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Re: [Ron.M] Bridge rectifier putting out approx 170VDC? [In reply to]	Can't Post

Doh! You are right.. it's a Zeinith. Completely forgot.
I'll toss the manual on my website here:
http://www.onecircuit.com/sites/onecircuit.com/files/temp/SY3572DT_SVM.pdf

Actually an EE and have tons of experience with digital design.. just not so much with the analog. ;)
And I also collect and repair classic arcade games on the side but I stick mainly to the game PCB repair since it's 99% digital.
http://www.onecircuit.com/

I've done some monitor rebuilds but nothing major. (Flyback replacements, cap-kits, etc).
But I have my own lab here so I'm fully capable of going through this chassis if you can provide some guidance.
Thanks!
-Adam
==================
http://www.onecircuit.com
==================

mel
Veteran

Mar 15, 2012, 10:20 PM

Post #6 of 32 (4720 views)
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Re: [ajcrm125] Bridge rectifier putting out approx 170VDC? [In reply to]	Can't Post

Check QX3208

Ron.M
Veteran

Mar 15, 2012, 10:41 PM

Post #7 of 32 (4720 views)
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Re: [ajcrm125] Bridge rectifier putting out approx 170VDC? [In reply to]	Can't Post

ajcrm125;.....

I'm having a problem with downloading recently...
Having a problem trying to find the cause & fix it... Unsure

...
No matter where I go to download manuals , my computer stops downloading at exactly 3.79 MBs... Mad

...
Damdest thing I ever saw... Pirate

...
Any ideas ???
I'm trying to download yours & I'll let you know how it goes...
At 16.7 MB , it'll be interesting to see how much I get...
(So far , so good !!!...Downloaded 8.32 MBs as I post this)...
THANKS for the link..... Smile

...

...

In the meantime;....
Check the volts on ICX3431....(5 pins)...
That's the power supply IC...
Should be a STR53041...
Use Hot ground as a reference...
Negative side of CX3405 is a good place for that .....

Also unplug TV & short to chassis ground (Tuner cover is a good place for that) the collector of the HOT (Horizontal Output Transistor) at the flyback...
Then read ohms from collector to chassis ground...
Please post ALL readings...

THANKS.... Sly

....

Later...Ron.M.... Cool

...
Veteran & Retired TV technician

mel
Veteran

Mar 16, 2012, 12:00 AM

Post #8 of 32 (4714 views)
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Re: [Ron.M] Bridge rectifier putting out approx 170VDC? [In reply to]	Can't Post

You can download the Zenith GX chassis service manual at Elektrotanya.com. The 16.1 meg file will take a long time on dial up but it should work.

Ron.M
Veteran

Mar 16, 2012, 12:23 AM

Post #9 of 32 (4712 views)
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Re: [mel] Bridge rectifier putting out approx 170VDC? [In reply to]	Can't Post

ajcrm125;...

The number that mel posted lonely is for the Horizontal Output Transistor , QX3208..
It is on a heatsink just toward the front of the TV...

mel;....

Thanks , but , that's one of the sites I went to & could NOT download past 3.79 MBs...
The link from ajcrm125 worked PERFECT & I now have the FULL manual !!!!
I use Elektrotanya.com frequently & did not have any problems with it or the other sites till recently...
I'm going to do a complete re-install of IE7 later on...
It is a WIERD problem as it is affecting several sites...

Thanks again.....

Have a GREAT day & weekend.... Sly

...

Later...Ron.M.... Cool

...
Veteran & Retired TV technician

(This post was edited by Ron.M on Mar 16, 2012, 12:27 AM)

ajcrm125
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Mar 16, 2012, 1:12 AM

Post #10 of 32 (4704 views)
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Re: [Ron.M] Bridge rectifier putting out approx 170VDC? [In reply to]	Can't Post

Ok here's what I get for ICX3431:
Pin 1: 0
Pin 2: 8.8mv
Pin 3: 164.8v
Pin 4: 6.8mv
Pin 5: 35mv

I shorted pin 1 of the flyback to chassis ground (using lead to the tuner shield). I then measured the collector of the HOT to this same ground and it was a short.
-Adam
==================
http://www.onecircuit.com
==================

Ron.M
Veteran

Mar 16, 2012, 2:22 AM

Post #11 of 32 (4700 views)
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Re: [ajcrm125] Bridge rectifier putting out approx 170VDC? [In reply to]	Can't Post

ajcrm125;....

OK...
Now you need to completely remove QX3208 from the board & check ohms between the center pin & the outside pins...
Also read the ohms from pin 1 on the flyback to chassis ground...
Then , plug the TV in , turn it on & read the +dc volts from pin 1 on the flyback to ground...
Expect to get 130 vdc...
Please post ALL readings...

Do you have an ESR Meter ???

IF QX3208 IS shorted , chances are that the power supply will need parts as well.... Unsure

...
That's coming soon.......

THANKS.... Smile

....

Later...Ron.M.... Cool

...
Veteran & Retired TV technician

(This post was edited by Ron.M on Mar 16, 2012, 2:23 AM)

ajcrm125
New User

Mar 16, 2012, 1:25 PM

Post #12 of 32 (4689 views)
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Re: [Ron.M] Bridge rectifier putting out approx 170VDC? [In reply to]	Can't Post

Ok I'll do that today. Quick question... just to be clear.. chassis ground on this schematic looks like this correct?
http://www.cliparts101.com/files/845/42B0E3CF69FC2D9AADCBA2A7D1AFE69E/lrg_RSA_IEC_Ground_Symbol.png

Because I see another ground that looks like this:
http://static.seton.com/media/catalog/product/Electrical-Symbol-Labels-On-A-Roll-94784-ba.gif

I believe you called that one the hot ground?
-Adam
==================
http://www.onecircuit.com
==================

Ron.M
Veteran

Mar 16, 2012, 5:57 PM

Post #13 of 32 (4684 views)
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Re: [ajcrm125] Bridge rectifier putting out approx 170VDC? [In reply to]	Can't Post

ajcrm125;....

Quote

chassis ground on this schematic looks like this correct?
http://www.cliparts101.com/...EC_Ground_Symbol.png

Correct...That IS chassis ground...

Quote

http://static.seton.com/...-A-Roll-94784-ba.gif
I believe you called that one the hot ground?

Correct, that IS HOT (AC) ground..

Do not get confused when you take readings or you will be mislead by the readings...

Please answer this;=>....
""Do you have an ESR Meter ???""
And post the other requested info when you get a chance...THANKS.... Sly

....

Later...Ron.M.... Cool

....
Veteran & Retired TV technician

ajcrm125
New User

Mar 20, 2012, 4:15 PM

Post #14 of 32 (4634 views)
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Re: [Ron.M] Bridge rectifier putting out approx 170VDC? [In reply to]	Can't Post

Sorry.. I don't have an ECR meter but it looks like a pretty useful tool.

So I measured the HOT and here's what I get:
From B to C, I get 626Kohms in one direction, open circuit in the other. From C to E, 629K in one direction, open circuit in the other. B to E (just for kicks) is only 36ohms! That doesn't sound good....

I measured between Pin 1 of the flyback and ground and the resistance climbed a while until it finally settled at 13.9k

I'll plug it in and get that reading for you.
Thanks,
-Adam
==================
http://www.onecircuit.com
==================

Ron.M
Veteran

Mar 20, 2012, 5:32 PM

Post #15 of 32 (4631 views)
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Re: [ajcrm125] Bridge rectifier putting out approx 170VDC? [In reply to]	Can't Post

ajcrm125;...

Looks like the HOT (Horiz Output Transistor) is OK ....
B to E or E to B at 36 ohms is OK...
That HOT has a built in resistor between B & E...
Look on the face of QX3208 & post the number you see there....THANKS.... Smile

...

Quote

I measured between Pin 1 of the flyback and ground and the resistance climbed a while until it finally settled at 13.9k

We'll take a closer look at this later....

Later...Ron.M... Cool

....
Veteran & Retired TV technician

ajcrm125
New User

Mar 20, 2012, 7:16 PM

Post #16 of 32 (4626 views)
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Re: [Ron.M] Bridge rectifier putting out approx 170VDC? [In reply to]	Can't Post

HOT is labeled:
TZ 1167-01
-Adam
==================
http://www.onecircuit.com
==================

mel
Veteran

Mar 20, 2012, 11:29 PM

Post #17 of 32 (4612 views)
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Re: [Ron.M] Bridge rectifier putting out approx 170VDC? [In reply to]	Can't Post

I can't find a data sheet on the TZ1167 that shows an internal resistor between base to emitter but it crosses to an NTE2302. When I check a new one that I have leftover in the shop, it shows infinite both ways collector to emitter and front to back ratio base to emitter. Therefore, I still suspect the HOT. The resistance rising pin 1 of flyback to ground is the filter cap charging eliminating CX3220 (which usually shorts) as suspect. When ICX3431 (the other usual suspect) fails, it usually blows the main fuse so I don't think it is the problem.

Ron.M
Veteran

Mar 20, 2012, 11:55 PM

Post #18 of 32 (4611 views)
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Re: [ajcrm125] Bridge rectifier putting out approx 170VDC? [In reply to]	Can't Post

ajcrm125;.....

mel may be right....
But , I'm going to let that slide for now as subs have a tendency to not be the same as the original....
The 121-01167-01 OR TZ1167-01 may have the resistor & may be OK...
The collector readings you gave seem OK...
Time will tell...

In case you are wondering why I did not reply , this is the reason;=>...

Quote

Then , plug the TV in , turn it on & read the +dc volts from pin 1 on the flyback to chassis ground...
Expect to get 130 vdc...

When I get that info , I'll proceed....
THANKS.... Sly

....

Later...Ron.M.... Cool

....
Veteran & Retired TV technician

(This post was edited by Ron.M on Mar 21, 2012, 7:55 PM)

ajcrm125
New User

Mar 21, 2012, 9:50 PM

Post #19 of 32 (4588 views)
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Re: [Ron.M] Bridge rectifier putting out approx 170VDC? [In reply to]	Can't Post

With the HOT removed I get 134v at pin 1 of the flyback.
-Adam
==================
http://www.onecircuit.com
==================

Ron.M
Veteran

Mar 21, 2012, 10:23 PM

Post #20 of 32 (4586 views)
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Re: [ajcrm125] Bridge rectifier putting out approx 170VDC? [In reply to]	Can't Post

ajcrm125;....

OK ....
Going for the jugular here....
Reinstall the HOT....
Hook up your meter to pin #3 on the flyback & turn the TV on...
Please post results....
Thanks.... Sly

...

Later...Ron.M.... Cool

...
Veteran & Retired TV technician

ajcrm125
New User

Mar 21, 2012, 11:17 PM

Post #21 of 32 (4581 views)
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Re: [Ron.M] Bridge rectifier putting out approx 170VDC? [In reply to]	Can't Post

Also 134v.
-Adam
==================
http://www.onecircuit.com
==================

mel
Veteran

Mar 21, 2012, 11:18 PM

Post #22 of 32 (4581 views)
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Re: [Ron.M] Bridge rectifier putting out approx 170VDC? [In reply to]	Can't Post

How about installing a new just NTE2302 HOT and quit messing around. That is what I would have done from the get go.

(This post was edited by mel on Mar 21, 2012, 11:21 PM)

jts1957
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Mar 22, 2012, 12:19 AM

Post #23 of 32 (4577 views)
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Re: [Ron.M] Bridge rectifier putting out approx 170VDC? [In reply to]	Can't Post

Better yet - the current sub:
121-1167-01 .... NTE2353

-------------------------
Location: Far, Far Away

Ron.M
Veteran

Mar 22, 2012, 2:53 AM

Post #24 of 32 (4569 views)
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Re: [jts1957] Bridge rectifier putting out approx 170VDC? [In reply to]	Can't Post

jts1957;......

We have to forgive mel for his errors.... Unsure

....
I suggested he get a new pair of glasses on at least one occasion...
It might also be due to the "shake & bake" local where he is..

That said, I'm going to go to the bleachers & see how this plays out... Smile

...
So have at it folks.... Wink

...

Have a GREAT day & week..... Sly

....

Later...Ron.M.... Cool

...
Veteran & Retired TV technician

(This post was edited by Ron.M on Mar 22, 2012, 2:55 AM)

mel
Veteran

Mar 22, 2012, 4:12 AM

Post #25 of 32 (4563 views)
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Re: [jts1957] Bridge rectifier putting out approx 170VDC? [In reply to]	Can't Post

Per ajcrm125, HOT is marked TZ1167-01. NTE cross reference guide says replace with NTE2302. There probably is not the much difference between the two but I checked the part number he is replacing, not what the parts list says.

(This post was edited by mel on Mar 22, 2012, 4:21 AM)

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