I have a faulty SMPS from a HP Deskjet 960c (I know it's old!). Everything was fine, then after printing a few pages one morning, the printer just cut out, and now only turns on for a couple of seconds, if at all.
ASTEC AA21160, HP Part C6455-60009.
Input: 100-240v ~ 50/60Hz 0.9A
Output: 32v DC 30w
The main power transistor is a K2545
The controller (AS998N) looks to be obsolete.
I've set it up in a controlled environment, series light bulb (40w) on the input and electronic load on the output.
If I attempt to draw 200mA, all appears well.
If I attempt to draw 300mA, all appears well.
Somewhere around 320 - 330mA, it cuts out, i.e. at roughly 1/3 it's rated output.
I've been through all the components, i.e. diodes, capacitors, resistors, transistors etc. as best I can and everything seems ok. There are various SMD resistors and other bits which are tricky to get accurate readings from in circuit, but I've not spotted any shorts, opens or unrealistic values. Fuses remain good.
When it's in the printer and the PSU shuts down, the load obviously disconnects.
When using the electronic load, the load remains in place. In this scenario I'm not 100% sure if it shut down or went into a shorted condition on the input at the series light bulb appeared to stay on (I turned it off fairly sharpish, worried something may blow, causing more problems).
So it seems that something is failing under load. I have fixed various SMPS's in the past, but the issue is normally more obvious.
Any ideas on what may cause this scenario greatly appreciated.
Thanks.