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Crumbtrail TV Forums: TV Equipment: TV Repair Forum:
My old grundig is semi-dead

 

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t0nito
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Oct 25, 2013, 8:03 PM

Post #1 of 76 (3574 views)
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My old grundig is semi-dead Can't Post

Hi, I have an old grundig I replaced a tripler a few years years ago with Ron's help and it worked fine until now.

I turned it on one day and about 5 minutes later it made a screeching noise with a few faint lines on the screen for 2 or 3 seconds, made a loud bang and turned off (as in standby). I turned it on with the remote and it made a loud bang and it went to standby again. When I took the cover of to inspect where the noise was coming from I turned it on and (of course) to make things difficult it woudn't do the noise again.

Now when I turn it on, the LED display (no OSD) shows as if it were on (AV, 1, 2, 3 etc) but it won't actually turn on.

I have a working flyback that I replaced because it made a loud 15 kHz squeal, but I know it's working so I swapped it but it's still dead.

I tested the HOT with a multimeter for continuity (in circuit though) and there is no continuity between the 3 pins.

Visually inspecting nothing seems burned or charred.

Chassis is a CUC3400 schematic is here:

http://www.eserviceinfo.com/download.php?fileid=247


I know it's a really old set but it has RGB input and had a really nice shapness and colour. It's a nice TV for retro gaming.

Thank you


(This post was edited by t0nito on Oct 25, 2013, 8:06 PM)



Ron.M
Veteran


Oct 26, 2013, 12:38 AM

Post #2 of 76 (3566 views)
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Re: [t0nito] My old grundig is semi-dead [In reply to] Can't Post

 
t0nito;....

Well , lets see what we can do this time....
How long is the red wire on the flyback ???
What I'd like you to do is disconnect the wire from the flyback at the trippler end & safely suspend it in space away (At least 6") from all other wiring , metal & the trippler..
Reason is that that wire will have ~5,000+ volts on it & will have a tendency to jump when the set is on...
Turn the TV on & see if there is a small bluish corona coming off the end of that wire..
You may have to darken the room to see it...
Post results...


Quote
I tested the HOT with a multimeter for continuity (in circuit though) and there is no continuity between the 3 pins.

According to the service manual that I downloaded (Your link,THANKS !!!) , you should read about 100 ohms between base & emitter of T661 ..
That would be point "P" on the schematic & the junction of "R660" & "L660"..
There are 2 junctions for those 2 components , either one will work for your readings...
You should read ~0.0 ohms between the emitter & point "P" ...


Later...Ron.M...Cool...
Veteran & Retired TV technician


t0nito
User

Oct 26, 2013, 9:06 AM

Post #3 of 76 (3560 views)
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Re: [Ron.M] My old grundig is semi-dead [In reply to] Can't Post

Hi Ron, thank you for your reply, as for the wire, the flyback has a soldering pad were the wire is soldered to the tripler. Do you mean that I should disconnect that wire from the flyback and check the corona on the pad?

If you think it's unsafe to do so because of the arcing should I solder a long wire away from the set and check at the tip of that wire?

I can test that but I'm pratically sure there's no HV as I don't hear any 15kHz ring.

Also I'll test the HOT later and post the results.


t0nito
User

Oct 26, 2013, 9:55 AM

Post #4 of 76 (3559 views)
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Re: [Ron.M] My old grundig is semi-dead [In reply to] Can't Post

Measuring directly on the transistor legs I get 0 Ohm between Base and Emitter.


Ron.M
Veteran


Oct 26, 2013, 5:22 PM

Post #5 of 76 (3550 views)
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Re: [t0nito] My old grundig is semi-dead [In reply to] Can't Post

t0nito;....

Hold off on the flyback wiring test...
Time to remove the HOT (Horizontal Output Transistor) from the set & check ohms between all 3 legs...
Especially from the collector to base & the emitter...
Post results.....
Thanks...

Does the red wire on the flyback disconnect from the flyback or on the trippler or both ???

Later..Ron.M....Cool...
Veteran & Retired TV technician


t0nito
User

Oct 26, 2013, 7:29 PM

Post #6 of 76 (3547 views)
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Re: [Ron.M] My old grundig is semi-dead [In reply to] Can't Post

OK, so the HOT (T521):

Emitter to Base: 0 Ohm
Collector to Emitter 5.20 MOhm
Collector to Base 2 MOhm

EDIT: That's odd, I now get 98 Ohm between Base and Emitter of T661 I could have sworn it was 0 Ohm this morning, maybe I was still half asleep.


(This post was edited by t0nito on Oct 26, 2013, 7:59 PM)


Ron.M
Veteran


Oct 26, 2013, 9:37 PM

Post #7 of 76 (3538 views)
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Re: [t0nito] My old grundig is semi-dead [In reply to] Can't Post

 
t0nito;.....

Forget something;=>...

Quote
Does the red wire on the flyback disconnect from the flyback or on the trippler or both ???

This is important !!!...

Also , reverse the meter leads & reread the ohms;=>...
Base to Emitter;
Base to Collector;
Emitter to Collector;

Is the reading from Emitter to Base dead bang zero ???....
No resistance at all ???


Thanks....

Later...Ron.M...Cool..
Veteran & Retired TV technician


t0nito
User

Oct 26, 2013, 10:06 PM

Post #8 of 76 (3536 views)
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Re: [Ron.M] My old grundig is semi-dead [In reply to] Can't Post


In Reply To
...as for the wire, the flyback has a soldering pad were the wire is soldered to the tripler


The wire is "hard wired" on the tripler end and is connected to the flyback to the pad.

I lowered the scale and emitter to base is 47 Ohm with the meter leads either way,

Reversing the leads show same results as before.


(This post was edited by t0nito on Oct 26, 2013, 10:07 PM)


Ron.M
Veteran


Oct 26, 2013, 10:29 PM

Post #9 of 76 (3527 views)
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Re: [t0nito] My old grundig is semi-dead [In reply to] Can't Post

  
t0nito;...

Having a problem trying to figure out what you mean...

Quote
The wire is "hard wired" on the tripler end and is connected to the flyback to the pad.


OK...
Does that mean you have a wire coming out of the trippler & is soldered to a pad on the flyback ???
Maybe a pix would help ???


Also , lets try this again;=>...
Base to Collector;
Emitter to Collector;


Quote
Reversing the leads show same results as before.

Is that true for the above also ???


Later...Ron.M....Cool...
Veteran & Retired TV technician

(This post was edited by Ron.M on Oct 26, 2013, 10:31 PM)


t0nito
User

Oct 26, 2013, 10:43 PM

Post #10 of 76 (3522 views)
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Re: [Ron.M] My old grundig is semi-dead [In reply to] Can't Post


In Reply To

Quote
OK...
Does that mean you have a wire coming out of the trippler & is soldered to a pad on the flyback ???


Exactly


Quote
Is that true for the above also ???


Yes the values are the same as before if I reverse the leads...



(This post was edited by t0nito on Oct 26, 2013, 10:44 PM)


Ron.M
Veteran


Oct 26, 2013, 10:53 PM

Post #11 of 76 (3516 views)
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Re: [t0nito] My old grundig is semi-dead [In reply to] Can't Post

t0nito;...

OK...


Quote
Collector to Emitter 5.20 MOhm
Collector to Base 2 MOhm

Concerning the readings above;....
Are they the SAME as this when you reverse the meter leads ???
Emitter to Collector 5.20 MOhm ???
Base to Collector 2 MOhm ????
If so , the transistor is bad !!!



Later...Ron.M....Cool...
Veteran & Retired TV technician


t0nito
User

Oct 26, 2013, 10:54 PM

Post #12 of 76 (3515 views)
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Re: [Ron.M] My old grundig is semi-dead [In reply to] Can't Post

Yes, that is correct, now the thing is, what made it blow or what blew with it, right?


(This post was edited by t0nito on Oct 26, 2013, 10:55 PM)


Ron.M
Veteran


Oct 26, 2013, 10:56 PM

Post #13 of 76 (3512 views)
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Re: [t0nito] My old grundig is semi-dead [In reply to] Can't Post

t0nito;....

What is the number on that transistor ???


Later...Ron.M...Cool...
Veteran & Retired TV technician


t0nito
User

Oct 26, 2013, 11:03 PM

Post #14 of 76 (3507 views)
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Re: [Ron.M] My old grundig is semi-dead [In reply to] Can't Post

BU508D


Ron.M
Veteran


Oct 26, 2013, 11:17 PM

Post #15 of 76 (3506 views)
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Re: [t0nito] My old grundig is semi-dead [In reply to] Can't Post

 
t0nito;.....

BU508D IS BAD !!!!!

With the transistor out of the set , go to the collector pin with your meter set at +DC volts on a range that will read ~150 VDC..
Turn the TV on , read the volts & post results..

Then get an exact replacement , not a sub....
When you do , unsolder the lead going to the trippler....
Post back when you get the replacement & we'll go from there..


Later..Ron.M...Cool..
Veteran & Retired TV technician


t0nito
User

Oct 26, 2013, 11:20 PM

Post #16 of 76 (3503 views)
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Re: [Ron.M] My old grundig is semi-dead [In reply to] Can't Post

Is that with the transistor on the board or measuring on the pad where it used to be?

Oops sorry "With the trasistor out of the set"

I was distracted


(This post was edited by t0nito on Oct 26, 2013, 11:26 PM)


t0nito
User

Oct 26, 2013, 11:31 PM

Post #17 of 76 (3496 views)
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Re: [Ron.M] My old grundig is semi-dead [In reply to] Can't Post

I'm only getting 5V between ground and the collector


Ron.M
Veteran


Oct 26, 2013, 11:43 PM

Post #18 of 76 (3495 views)
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Re: [t0nito] My old grundig is semi-dead [In reply to] Can't Post

t0nito;.....

Are you using the ground that is connected to the emitter of T521 (R523) ???
Check the B+ pin on the flyback..
This schematic is a bit confusing...
On page 2 , the pin # should be 16 or 17...
Also try pins 15 & 24 for the same voltage...

Later...Ron.M...Cool...
Veteran & Retired TV technician


t0nito
User

Oct 26, 2013, 11:45 PM

Post #19 of 76 (3491 views)
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Re: [Ron.M] My old grundig is semi-dead [In reply to] Can't Post

I was doind between chassis ground and collector.

-5v for stand by
-12V when on

The pins on the board are from A to O (no K)


(This post was edited by t0nito on Oct 26, 2013, 11:55 PM)


t0nito
User

Oct 27, 2013, 12:00 AM

Post #20 of 76 (3483 views)
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Re: [t0nito] My old grundig is semi-dead [In reply to] Can't Post

There is at least one pin that shows 175V in this case pin B


(This post was edited by t0nito on Oct 27, 2013, 12:01 AM)


Ron.M
Veteran


Oct 27, 2013, 12:05 AM

Post #21 of 76 (3481 views)
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Re: [t0nito] My old grundig is semi-dead [In reply to] Can't Post

t0nito;.....

Please give me ALL the information I ask for...Shocked.
NOT bits & pieces !!!..Crazy...


Quote
Are you using the ground that is connected to the emitter of T521 (R523) ???
Check the B+ pin on the flyback..
In the manual on page 2 , the pin # should be 16 or 17...
Also try pins 15 & 24 for the same voltage...

This schematic IS confusing...
The ground you are using (Chassis ground) may NOT be the SAME ground as the one from the emitter of T521...
I would also like to see readings from the other pins on the flyback...


PS:..
I will be going offline soon...
(After you get the readings I asked for)...


Later..Ron.M...Cool...
Veteran & Retired TV technician


Ron.M
Veteran


Oct 27, 2013, 12:09 AM

Post #22 of 76 (3475 views)
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Re: [t0nito] My old grundig is semi-dead [In reply to] Can't Post

t0nito;....

Pin "B" is the primary B+ for "T661"...
EDIT;... AND it is NOT chassis ground !!!!!
That is a "Hot Ground"...


Look for pins "M" , "L" or "N"...


Later...Ron.M...Cool...
Veteran & Retired TV technician

(This post was edited by Ron.M on Oct 27, 2013, 12:12 AM)


t0nito
User

Oct 27, 2013, 12:10 AM

Post #23 of 76 (3474 views)
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Re: [Ron.M] My old grundig is semi-dead [In reply to] Can't Post

Between R523 and collector I get -15V on standby and -18 when on.

I can't get readings because as soon as I touch the meter lead on pin 1 (ground) of the flyback the meter goes haywire on me.



This schematic is from this flyback but it's confusing as pin A (1) doesn't look like ground to me.

Anyway, between chassis ground and B: 175
L: -10v
M -10v
O -8v


(This post was edited by t0nito on Oct 27, 2013, 12:16 AM)


t0nito
User

Oct 27, 2013, 12:18 AM

Post #24 of 76 (3470 views)
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Re: [t0nito] My old grundig is semi-dead [In reply to] Can't Post

Sorry I saw the ground thing after I replyed.

So where should I put the other end of the meter? because if it's on pin A the meter goes crazy


Ron.M
Veteran


Oct 27, 2013, 12:19 AM

Post #25 of 76 (3469 views)
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Re: [t0nito] My old grundig is semi-dead [In reply to] Can't Post

t0nito;....

OK ....
Lets get a new transistor & we'll go from there...
Apparently , they're using high frequency to get the B+ to T521...

But , dont forget to unsolder the trippler from the flyback...

Have a GREAT day & weekend & we'll see you when you get the transistor...


Later...Ron.M....Cool...
Veteran & Retired TV technician

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