GRUNDIG CRT TV keeps blowing fuse

[omerfbingol]

Hello everyone,

I have here a Grundig ST 70-702 TOP Television (CUC 2032) that keeps blowing the SI62501 numbered (2.5 A) fuse as soon as the POWER button is pressed. There seems to be no other blown/burnt component on the board.

The fuse can be seen, on service manual's page 26 (section 3-4) at coordinates X:270, Y:75. I marked it with a red rectangle on the photo.

I have no experience in TV repair, other than fixing some cold solders. I referred to the service manual, looking for a predetermined repairing sequence related to this particular fuse, but it appears that I'll need to find out the solution by trial, based on professional repairing experience, which I have none.

This TV belongs to my grandpa and it would be nice if this thing wouldn't go to trash: that's why I'm clinging onto it

The error occured first at a rural town with a poorly regulated grid, making it plausible that the fuse was blown because of high voltage, so I first thought that simply replacing the fuse will work, but it didn't. It kept blowing 2 more fuses I put in.

Could anyone point me towards a possible solution?

Thanks in advance.

 

[ramondo]

REMAIN CALM,,, ALL IS WELL.

Most likely fault is with the bridge rectifier (4 pin device with chamfered corners and hole in center) located above large capacitor. Look up online,testing rectifiers. Ohm meter and soldering iron.

 

[ronsimpson]

bridge rectifier

 

[omerfbingol]

REMAIN CALM,,, ALL IS WELL.

Most likely fault is with the bridge rectifier (4 pin device with chamfered corners and hole in center) located above large capacitor. Look up online,testing rectifiers. Ohm meter and soldering iron.

Thank you very much, I'll tell my grandpa not to throw it away I will be back with updates.

View attachment 120757

Thank you

 

[Nigel Goodwin]

REMAIN CALM,,, ALL IS WELL.

Most likely fault is with the bridge rectifier (4 pin device with chamfered corners and hole in center) located above large capacitor. Look up online,testing rectifiers. Ohm meter and soldering iron.

Sorry, but I would disagree.

The bridge rectifier is ONE possibility, but it's only a very slight one.

In my previous job I was a TV engineer, and we were a MAJOR UK Grundig dealer, and I've repaired vast number of Grundig TV's, including many of this series.

By far the most likely problem is multiple component failures in the PSU, the bridge is one part that gets blown, the IC (TDA4605) blows, the chopper FET T60006 blows, plus various other components - I used to have two component drawers at work, one with all the parts for the FET version (like this one) and one for the bi-polar version (basically drawers of repair kits). I can't remember what were all the parts were now, I've not done one MANY years, not since the demise of CRT. But I would replace C60011, R60006, R60005,and D60005. I would also suggest changing the main electrolytic (C60022), these go O/C and cause the PSU to 'explode' on Grundig's.

First off I would suggest checking across drain and source of T60006, if it reads S/C, remove it - and check it again - if it reads S/C when removed, then you need to replace the parts I suggested, and any other faulty ones. If you don't replace all the faulty ones, it will just go bang again when you turn it on.

If the FET doesn't read short when removed, then it 'may' just be the bridge - in which case I suggest you go out and buy a lottery ticket

The much older Grundig TV's commonly blew just the bridge, but not the later ones.

 

[ramondo]

I agree with Nigel 100%,, if not rectifier (easiest for novice to check) then you have to decide how much further you want to go.

 

[wkrug]

First thing i would do is to replace SI60001.
So the complete Switching Supply is OFF grid then.
When SI62501 would be blown again the damage is in the rectifier section, or C60018 is blown.

Whe the error is in the Switching Supply it can be on primary, or secondary side of the Part and it would be much harder to find.

When measuring around at the primary side of the Power supply I suggest to use an isolation transformer.