STP6005 Power Supply

[mike123333]

I have a power supply that has not been used much, several months ago I went to use it and as I was setting up the voltage and amperage I heard a loud pop and the unit turned off. The main fuse was blown. I replaced the fuse and it turned on but was unable to set voltage or amperage, they both stayed at 0.

upon inspection I found the 2 Mosfets blown along with 2 resistors. The mosfets are PTA09N50 and a 68 and 10k resistors.

I replaced the components and turned it on, there was no blown parts but the voltage only went up to 2.2V, I turned the unit off and after a while started to toublshoot it, upon turning the unit on the mosfets blew and one of the resistors went open. The main fuse was also blown

I was unable to find any shorts, any input would be greatly appreciated. please see photos for better illustration.

the second time I removed the mosfets I ended up peeling back a trace, I will have to repair that.

[stj]

Re: STP6005 Power Supply

if the mosfets gad shorts to the gate then you need to examine the drive circuit

[mike123333]

Re: STP6005 Power Supply

One Mosfet is shorted gate to drain and the other is shorted gate to drain and source.
Would the likely area be in the hot side or could the cold side cause an overload. the optocoupler does not seem to be shorted at all.

[stj]

Re: STP6005 Power Supply

optocouplers dont usually short, they go open
what drives the gate pins

[mike123333]

Re: STP6005 Power Supply

I sketched out a rough schematic, these go to the red transformer, the drains are tied together to another transformer.

[stj]

Re: STP6005 Power Supply

thats a flashback, not seen a transformer used as a base amplifier since the 1970's!!
so check the windings are good i suppose, and check whatever drives the transformers

[mike123333]

Re: STP6005 Power Supply

I could not find anything wrong, as I researched this power supply further, I found that this is a common failure to this device, some people reported right out of the box blowing the main fuse. Apparently this is appears to be a design flaw, I am unsure how it worked several times then blew.

I wish there was a way to correct the design flaw and get this working instead of sending it to the landfill.

any ideas?

[stj]

Re: STP6005 Power Supply

maybe the transformer is leaky?
it actually reminds me of an AT psu,
i'll look for some schems if you tell me the chip number.
maybe the chip or small cap is bad?

[mike123333]

Re: STP6005 Power Supply

maybe the transformer is leaky?
it actually reminds me of an AT psu,
i'll look for some schems if you tell me the chip number.
maybe the chip or small cap is bad?

which chip are you referring to?

[mike123333]

Re: STP6005 Power Supply

what I find hard to believe is the amount of failures on this unit with little to no usage.

[stj]

Re: STP6005 Power Supply

the 8pin chip next to the optocoupler

[mike123333]

Re: STP6005 Power Supply

the 8pin chip next to the optocoupler

I checked this chip out for shorts and could not detect anything.

[jiroy]

Re: STP6005 Power Supply

Lot of times , experimenting on transformers , I would find an internal hidden fuse . Maybe not in your case , but worth mentioning .

[mike123333]

Re: STP6005 Power Supply

Lot of times , experimenting on transformers , I would find an internal hidden fuse . Maybe not in your case , but worth mentioning .

Thanks for the information, but why would the mosfets blow if a fuse has blown in the transformer? the fuse you mention would that be part of the windings, I do not have any open windings or shorts from primary to secondary.

[jiroy]

Re: STP6005 Power Supply

Thanks for the information, but why would the mosfets blow if a fuse has blown in the transformer? the fuse you mention would that be part of the windings, I do not have any open windings or shorts from primary to secondary.

For three simple reasons , first , it could have been a simple electric surge that sometimes take out many components , and second because you said you didn't detect any shorts now .. And the third , you have to consider any possibility at hand .

[mike123333]

Re: STP6005 Power Supply

Would this fuse be located deep inside the transformer or just below the plastic wrapping ?

[jiroy]

Re: STP6005 Power Supply

Would this fuse be located deep inside the transformer or just below the plastic wrapping ?

Always deep inside ..

By the way , and in another review , you said also "I removed the mosfets I ended up peeling back a trace" . So check if you removed a trace pin between dual sides of pcb .

[mike123333]

Re: STP6005 Power Supply

Always deep inside ..

By the way , and in another review , you said also "I removed the mosfets I ended up peeling back a trace" . So check if you removed a trace pin between dual sides of pcb .

Would this fuse be located on the primary or secondary side or both? Also is shouldn't this show up with metering the windings and if there is an open on the ohms reading then that would indicate that there is a break?

[jiroy]

Re: STP6005 Power Supply

Would this fuse be located on the primary or secondary side or both? Also is shouldn't this show up with metering the windings and if there is an open on the ohms reading then that would indicate that there is a break?

It could be on any side , it depend on manufacturers/designs . One affirmative thing , it's always one , but not 2 .. And remember , bad varnishing due to surges may play lot of confusing scenarios too .