1084ST Won't power on.

[KBQ]

Well it'd be easier than me ****ing away dozens of fuses... A look round the internet said take the posistor out and see what happens, replaced HOT again, didn't change a thing. Tempted to kick it out the window.

When my funds have recovered I think I'll take you up on your offer. I'm 80 quid in the hole on this thing, unemployed and the rent is due on monday.

 

[roy_bates]

ok,when your ready theres no rush...just dont power it on anymore.

im happy to do the work just for parts,its easier that way besides i cant find any schematics or service manual for this one.
its better if someone like me looks at it.

 

[idrougge]

1084ST monitors often fail due to a broken TDA4605.

 

[chiark]

I've been given a 1084ST that's faulty from a local friend.
The PSU appears to be going into protection mode (LED comes on, monitor whines for a second, PSU shuts down for a second, repeat...) suggesting there's something wrong downstream of the PSU.
I've ordered a replacement HOT and LOPT, along with the TDA4605.

I'm going to remove the LOPT in the meantime and also check for short on the HOT to confirm that the problem is LOPT related. My strong suspicion is that a LOPT winding insulation has failed, shorting out, taking out the HOT and causing the PSU to panic.

 

[chiark]

LOPT removed, and the PSU no longer shuts down... This suggests to me that the LOPT is causing the fault... Probably over simplifying things, but I'm hopeful.

 

[EzdineG]

Make sure you replace that HOT if you’re replacing the LOPT.

One can definitely cause the other to blow

 

[chiark]

Thanks for that - given it was less than £1 for the HOT (and also for the power supply controller chip) I thought it worthwhile to get one. I'll make sure I change it. It was about £50 all in for the bits plus shipping.

The LOPT was surprisingly simple to remove - I was expecting a fight with the solder .

Found this on YouTube which I thought was extremely straightforward, too:
[FONT=Verdana,Arial,Tahoma,Calibri,Geneva,sans-serif]https://www.youtube.com/watch?v=YWE6-1AewLc[/FONT]

 

[chiark]

LOPT and HOT arrived today! Yay!
Replaced both! Woo!
Powers up and stays powered up! Good...
Still black screen! Boo.

There is now a 'hum' from the flyback and a 50Hz tick, however adjusting focus/screen, checking inputs, etc, and I still have a black screen. Whilst I'm here I might as well replace the 4605 too, but I'm doubtful on that as it wouldn't power up if that was not working...

 

[EzdineG]

Do you get any static at the screen when powered up? Do you see the heater lighting up at the back of the tube?

 

[chiark]

Changed the 4605 too, still a black screen.

I can't see any obvious glow from the heater, and no static. There's a slight buzzing from the suction cup, so I've removed, cleaned and reseated. Still no joy...