EEVblog Electronics Community Forum

Electronics => Repair => Topic started by: Dipski on January 11, 2017, 03:19:06 pm

Title: PSU with Unconnected Anode Lead
Post by: Dipski on January 11, 2017, 03:19:06 pm

Hi folks,

  I've got an Apple Mac that I'm working on, due to configuration issues I'm not able to connect the Analog Board (w/ PSU), Motherboard and CRT all together. One of the voltages from the PSU is slightly low so I'd like to run it with some load - the only problem being that the motherboard connects to the PSU via. the Analog board (which has the Flyback transformer).

  Do I risk any damage to the Flyback transformer powering it on disconnected from a CRT?

Title: Re: PSU with Unconnected Anode Lead
Post by: Ian.M on January 11, 2017, 04:10:11 pm

If the EHT lead arcs to anything you are likely to blow stuff up.  The Flyback transformer will probably survive but you risk blowing the line output transistor + any semiconductors on whatever board it arcs to.   Don't do it unless you can insulate the lead end to better than 25KV.

Also running a line output stage without the scan coils connected is also potentially disastrous.

If you've got the analog board schematic, you may be able to run it safely after isolating the supply to the line output stage.