Fuse /Power supply troubleshooting

Thank you I was wondering about the glue that makes sense now

I attached some pictures of readings and the bridge rectifier mine doesn't have a tilde (side ways S) it just says AC which makes sense since that is the symbol for AC.

my multimeter isn't auto ranging and after today I'm considering upgrading it.

Giovanni is using the meter on the diode setting, so the reading is the forward voltage.

Giovanni Laucella wrote:

 

Thank you everyone for you advise. I not sure I'm going to use this power supply again because I still don't trust my self yet with lethal voltages. I am in the USA so its 120v but still kind of scary.

Hi Giovanni,

Just for reference, even though you are in the US with "only" 120V, if you were working on an AC/DC converter that included power factor correction the nature of how the PFC works usually involves the voltage being boosted to much higher, so you could end up with voltages in the range of 400V on large capacitors so you are very right to be cautious when working on this type of circuit.

Best Regards,

Rachael

Hi Jon,

Good catch. After I turned off the computer and walked away it dawned on me that he was using the diode test and not the Ohmmeter. Always difficult to trouble shoot with limited access to info.

John

Hi Giovanni,

Based on your pictures it looks like the Bridge is OK. Just be sure you can get approximately .62 Volts from the plus to each of the AC and from the minus to each of the AC. The information I gave you before was based on the assumption that you were testing the diodes with the Ohm meter set on Rx1.

John

Thank you everyone I will continue to test.

Rachael I didn't know that, I will look more into PFC they sound interesting. this power supply has been sitting for a few months so that should help. Do you have any recomedations of what precations I should take or look out for.

Giovanni Laucella wrote:

 

Rachael I didn't know that, I will look more into PFC they sound interesting. this power supply has been sitting for a few months so that should help. Do you have any recommendations of what precautions I should take or look out for.

Hi Giovanni,

There are quite a lot of interesting things to be learning about power supplies. Its a fascinating topic when you get into it Unfortunately it's an area which is considered by a lot of people as a black art and they shy away from it, but when you start to look further into it, there's lots of fun to be had!

If you are working on an PSU that is powered off, just make sure all the capacitors have been discharged so there can be no retained high voltages before you handle it and you should be fine. If in the future you are considering debugging a misbehaving power supply "live" then that's entirely different and you'll need more test equipment such as an isolation transformer (this helps with safety), an oscilloscope with high voltage differential probes, and possibly an AC/DC current probe. I'd not recommend attempting this until you are very familiar with how these power supplies work and know where all the dangerous bits are and have the knowledge and experience to be able tackle this more safely.

Best Regards,

Rachael

Giovanni Laucella wrote:

 

my multimeter isn't auto ranging and after today I'm considering upgrading it.

A decent multimeter can make the world of difference to the success and enjoyment of this hobby, you don't have to spend a fortune on one, just make sure you get a reasonable brand one and not a cheap one, especially if you are doing any work on AC power supplies as the cheap ones that claim certain protection ratings on their inputs often really aren't designed well enough to actually adhere to those ratings and can be dangerous. You're probably already familiar with the EEVBlog but if not head over to the YouTube channel and look at some of Dave's videos on decent multimeters to get and ones to avoid. He even does a decent EEVBlog branded one now that he did in partnership with one of the multimeter manufacturers.

Besides, even if your current one is fine, having more than one, or many can be beneficial as there are often times that making simultaneous readings will speed things up a lot (e.g. PSU efficiency testing).

Best Regards,

Rachael

Here's a good reference for Power Supplies.

http://www.hammondmfg.com/pdf/5c007.pdf

The DC voltage on the filter capacitor for your supply with the Bridge Rectifier is 120 x 1.414 = 169.68 volts give or take a little.

Caution is a good idea.

The others are giving great advice, so I'm sure you'll eventually work out what went and took out the fuse.

Mark