Volumetric doser controller without opto-isolator on dry contact input

[sysrq]

Bipolar stepper motor H-bridge MOSFET output transistor burned out together with 100nF ceramic capacitor (in parallel between earth and +24V rail) and resettable PPTC fuse after someone decided to apply 110 AC voltage on dry contact input terminals. They said everything was working for couple of hours only with some flickering (due to AC input signal).

Manufacturer forgot to add some optocoupler or induction based coupler.

WITTMANN BATTENFELD - DOSIMAX MC Basic - Volumetric dosing - Blending - Auxiliary Equipment

Microcontroller NPN input tranistor seems intact as current there wasn't that high.

 

[Marvo]

Sounds like it reeked some havoc on the input stage but also sounds repairable if it's just discreet components like FETs, transistors, fuse and cap. Most manufacturers wouldn't i-couple or optocouple to isolate unless there are more issues at stake other than a few input-stage components.

 

[sysrq]

Thanks for answer. I will replace damaged components tomorrow and then see what happens. Sometimes it works successfully.

I guess it's not worth for the manufacturer to use opto-isolator if there is only one input.

 

[sysrq]

Unfortunately mosfet driver ic with unknown part number (L638SED E920 or 6K374, google can't find anything) is compromised as well, so this board is rubbish now.

 

[Marvo]

If it's taken the driver IC then it will require a complete control board. Some manufacturers run an exchange system where you mail the old one to them and you get a repaired board back that usually carries a warranty. It's a lot cheaper but not always available as an option.

 

[sysrq]

Turns out it's a L6388ED not L638SED.

I think ic manufacturer have made a mistake used ''S'' instead of ''8''.

 

[Marvo]

I'm not sure about them making mistakes :nonod:, the L638SED doesn't appear in any of my reference books but it maybe a proprietary variation of the L6388ED specifically for that controller card maybe with different bootstrapping arrangements for example.

 

[sysrq]

I'm not sure about them making mistakes :nonod:, the L638SED doesn't appear in any of my reference books but it maybe a proprietary variation of the L6388ED specifically for that controller card maybe with different bootstrapping arrangements for example.

I think then it's not commercial one.

Sometimes they may mark components differently to make them unrecognisable in order to avoid unauthorized repairs.

 

[sysrq]

Why was that site unsafe?

 

[Lucien Nunes]

after someone decided to apply 110 AC voltage on dry contact input terminals

Ha, a friend told me about a control panel that had been built and supplied with contact closure inputs labelled from A to Z. They got a call saying it had gone bang when powered up, when they sent an engineer out he found 3-phase 400V connected to R, S & T, because they are the phase letters!