Grundig TV fuse keeps blowing

[dark666]

Hi.

Im repairing a Grundig CRT TV.
Heres how it goes, the fuse keeps blowing as soon as i press the main power.
The fuse used to actually break in pieces so I replaced the diode bridge, and the fuse started to burn black without break so I thought the the short circuit was "smaller".
Tested and replaced the PTC and also replace the power entrance transistor, and now the fuse just burns, no black marks it just becomes transparent with no burned marks.

I have he feeling that the shor circuit has become smaller, What can I be missing?
Tested the diodes near the transistor and they are fine.

Could it be the PSU VDR's?
Or the B+ Capacitor?
There should be a rectifier near the Capacitor but I can't seem to find none.

Also resoldered lots of cold solders throughout the circuit.

Thanks

 

[Nigel Goodwin]

If you gave a model number and chassis number (CUCxxxx) fior the TV perhaps we could make suggestions - however, it's likely that your random tinkering has also caused more damage.

 

[Chippie]

The fuse turning black on initial switch on indicates there is a dead short across the downstream side of the fuse....If the fuse is before the switch it is conceivable that the switch is defective, however now that the fuse wire is blown clear with no blackening may be indicative of something else..Usual suspects include s/c chopper transistor, s/c line output transistor or defective flyback/lop tx or even defective tripler

As Nigel says a model number would really help...and screen size....some chassis used the same board for both 90 and 110 degree tubes

 

[dark666]

TV model Grundig ST 70-713/8 Dolby

The TV is about 6 or 7 years old.

Thanks

 

[Nigel Goodwin]

TV model Grundig ST 70-713/8 Dolby

The TV is about 6 or 7 years old.

Thanks

Get the CUCxxxx number off the back - the manuals are filed under chassis numbers - but it's almost certainly a fair number of parts have failed. I'm off work now until Friday, but if you've posted the chassis number I'll tell you what parts to change.

 

[Chippie]

CUC 2130 methinks ?

Dont have it in my collection tho'

 

[Nigel Goodwin]

CUC 2130 methinks ?

Dont have it in my collection tho'

If it's the one with a large (TO3p) FET in the PSU, there's a resistor that goes high, this causes the FET and IC to self destruct.

 

[Chippie]

If it's the one with a large (TO3p) FET in the PSU, there's a resistor that goes high, this causes the FET and IC to self destruct.

In that case cold checks with a meter will determine if the chopper fet is s/c...

Cant recall the ic number probably one of the 8 pin TEA devices...?


Probably better to just get a repair kit will all the necessary parts...

 

[Nigel Goodwin]

In that case cold checks with a meter will determine if the chopper fet is s/c...

Cant recall the ic number probably one of the 8 pin TEA devices...?


Probably better to just get a repair kit will all the necessary parts...

Depends if kits were ever available for them? - I don't recall kits for them?.

 

[Chippie]

Grandata Online

Although the 2130 isnt listed

 

[mbarazeen]

connect some current limiting load in series to avoid fuse blowing every time when you test. it can be a 200W bulb. so the entire load will come to the bulb, when the fault is not there you can see the TV starts and the bulb goes to less brightness. this is how i always connect to check any SMPS to avoid damages.

 

[Nigel Goodwin]

connect some current limiting load in series to avoid fuse blowing every time when you test. it can be a 200W bulb. so the entire load will come to the bulb, when the fault is not there you can see the TV starts and the bulb goes to less brightness. this is how i always connect to check any SMPS to avoid damages.

He's already caused damage anyway, but even your scheme isn't a good idea - like I said, if he gives the chassis number, I'll post what needs replacing.

 

[dark666]

hi to all.
Sorry for the delay.

Nigel Goodwin, Here's the CUC number, CUC2130.
I was away for the past days.

Thanks

 

[dark666]

Grundig ST 70-713/8 Dolby
CUC2130

 

[Nigel Goodwin]

OK, I'll try and get time tomorrow to look out the manual.

 

[Nigel Goodwin]

I've just had a look, and I don't have a CUC2130 manual - which is strange, because as far as I'm aware I have ALL the Grundig manuals (as we used to be a Grundig main dealer).

So first off, what size and type is the chopper transistor?.

Beat in mind, unless you cure the CAUSE of the fault, any new parts you fit will instantly die, possibly causing more damage as well.

 

[costel32]

I've just had a look, and I don't have a CUC2130 manual - which is strange, because as far as I'm aware I have ALL the Grundig manuals (as we used to be a Grundig main dealer).

So first off, what size and type is the chopper transistor?.

Beat in mind, unless you cure the CAUSE of the fault, any new parts you fit will instantly die, possibly causing more damage as well.

Hi, I have read the topic because I kind have the same problem with a Grundig chassis CUC7350: blown fuse. I replaced 60011-60014 diodes, C60016, IC60030, T60020, C80029, R60027-28, D60024-23. I connected a 100W bulb instead the main fuse and to the power. The bulb lightens and goes out every 2 seconds. What else should I do? Can you help me with some advice?

 

[Nigel Goodwin]

Unfortunately we've thrown all the manuals and spare parts away for those sets now, there was quite a long list of parts I used to change on them - you might try checking the reservoir capacitor (the BIG one), those dry up and go low capacitance or even O/C.

 

[costel32]

Unfortunately we've thrown all the manuals and spare parts away for those sets now, there was quite a long list of parts I used to change on them - you might try checking the reservoir capacitor (the BIG one), those dry up and go low capacitance or even O/C.

Thank you!

 

[mbarazeen]

Hi, I have read the topic because I kind have the same problem with a Grundig chassis CUC7350: blown fuse. I replaced 60011-60014 diodes, C60016, IC60030, T60020, C80029, R60027-28, D60024-23. I connected a 100W bulb instead the main fuse and to the power. The bulb lightens and goes out every 2 seconds. What else should I do? Can you help me with some advice?

May be it would work, try to parellel another bulb, 100W may not be suffecient to give required volatge out at full load. You better disconnect output load with 100W bulb and see if you get stable regulated voltage output. if yes and bulb is dim or not glowing then you have dont a good work. Now with output load connected, try with parelleled bulbs based on the load current and voltage drop, even you can connect a cattle of 1000W accross the fuse.