Help to repair Metcal Mx500

[Chrisr3521]

So I've bought another Metcal MX500 for a spare and it doesn't want to heat the Iron (Iron has been tested ok) working through the document attached page two has voltages from working units, mine tests OK until I come to U4,

Pin 4 measures 261mv dc
Pin 5 bounces around low mv

However Pin 2 when switched on, light green and iron connected is measured at 56vdc not 18vdc like on my working unit, does this point to U4 being faulty?

any help welcomed on this

 

[JonSnell Electronic]

Quite possibly a short circuit switching transistor as this is a simple switching regulator; see attached.
Check to see if it is switching before condemning it.

 

[Chrisr3521]

Consider me stupid when it comes to electronics,

When you say switching, from low to high output?

 

[thimios]

Switching transistor is a part that switch at high frequency driven by a pulse width modulator .
Google smps for More informations

 

[jean-paul]

Repaired a few of its predecessor in the past and it were practically always bad solder joints with those.

Sorry, just checked and those were OKI Metcal PS-900. Bad joints and badly soldered output connector.

Off topic: never could discover their improvements over normal stations except that they heat up quickly.

 

[Chrisr3521]

OK, so how would I test for correct operation?

 

[quadtech]

Chris, my post here has a list of usual suspects -

https://www.eevblog.com/forum/repair/metcal-mx500p-11-power-comes-on-but-no-heat/

edit: oops - I see you are already on that forum for this

https://www.eevblog.com/forum/repair/need-help-with-a-metcal-mx500/25/

Another similar issue -
https://tinkerdifferent.com/threads/metcal-mx-500-repairs.2974/

 

[Chrisr3521]

Thanks @quadtech, thing that's throwing me is 56vdc on pin 2 of the lm2576 when the iron is attached