DIY repair on a vacuum cleaner circuit board

[Walter]

A mate had a short circuit on his Shark Navigator vacuum cleaner. We spent some time trying to get a local electrician to do a board level repair, but couldn't find anyone to do it. We called the Shark people and their solution was to trade the whole unit in and they would sell him a new one, because they don't have the parts.  Since this was 6 years old, I said we aren't going to lose anything by me trying (and I've said elsewhere, I'm not a handyman).

I knew it was a relay and diode that had blown, as I could see it, and using a multimeter I could see all of the other parts were ok, and all of the circuit paths were fine.

So I watched a few Youtube videos on circuit board repair (I've never done this before, and was convinced I was likely to make it worse - I'm OK at makiing a circuit), and I desoldered and removed the broken bits:

You can see the burned bit.  Underneath, the copper had been ruined at these spots this was my big fear at repairing, because scraping the circuit to expose more copper wasn't something I was confident at doing- I've ruined circuit boards before by using too much heat.  But I did it. In this photo you can see the broken copper:

Cleaned the burned bits with isopropyl alcohol.

The diode was a standard 1N4008 (and I have about 100 of them) so that was easy to solder in.

The relay was $7.95 locally bought.

Here's the fixed circuit so you can see my soldering:

Finished:

and it all works.  About 2 hours taking it apart, fixing and putting it back together.  $7.95 versus $400.00? No contest

[MikeTNZ]

Nice work!,

Appliances like this aren't usually made to be repaired easily, even opening them up can be quite a task.

As an electrician/ electrical technician in my day job, I fix a lot of stuff like this for friends and family during the weekends.

It seems strange how the relay and diode were affected, normally what happens is the bridge rectifier short-circuits and blows the fuse.

Cheers,

Mike T.

[Jason]

Hi @MikeTNZ,

Just wanted to extend an overdue but very warm welcome to the Workshop community. It's brilliant to have you join us as you obviously have a wealth of knowledge and experience to share. I trust you will also get some inspiration for your projects from our clever and creative community members. 

Please let me know if you ever need a hand getting the most from the site. I am always happy to help.

Thanks again for joining in the discussion on Workshop. We look forward to seeing more of your posts soon.

Jason

[Walter]

@sericom 

I tried to PM you, but could not.

I think the R4 resistor  is 1.5k in value.

Here's the full size photo.

[TedBear]

Just saw this one.  Great job of saving wastage by not throwing out a repairable item, and also saving money by doing it yourself.

If it happens again, or you come across another one, replace the 1n4004 with a 1n4007.  It's likely that the back-EMF from the relay is blowing the diode. The 1n4007 has a 1000v reverse voltage rating, whereas the 4004 is only good for 280 volts. (Chosen to ensure that the units will have a limited lifetime perhaps?)

[sericom]

Legend, thanks Walter, it's up and running again 👍

[r23on]

if the resistor is black, green , black, brown, Brown its a 500 ohm 1% if its black, green, black, red, brown its 5k ohms %1

also looking at on of the soldering joints there is the potential for further failure 

@TedBear Valid point re the, given the data from the data sheet the back emf would be very low and it being DC relay the finger may point more towards the diode 

https://www.futurlec.com/Relays/JQC-3FF-05.shtml 

[MitchellMc]

Welcome to the Bunnings Workshop community @sericom. It's amazing that you joined us, and it's great to hear @Walter has been able to assist.

Was it a Shark vacuum cleaner you were fixing or some other electronics?

We're keen to hear all about the projects and plans you have around the house and garden. Please feel free to let us know anytime you need assistance or have a project to share. As you've seen, our members are always happy to help wherever they can.

Mitchell

[sericom]

Thanks Mitchell, yeah it was the same model that Walter fixed, Shark Navigator. The dog had peed on the head and it blew a few resistors. It was one of my worst soldering experiences, the smell was horrid.

@r23on Pretty sure R4 will be a 1.5kΩ (Brown, Green, Black, Brown and Brown), very rare for resistors to start with a black band. 500Ω with 5 bands would be Green, Black, Black, Black and tolerance band. 5kΩ would be Green, Black, Black, Brown and tolerance.

[r23on]

Base on the photo the colours not the best but yes agree