Fixing a Broken Boss PSA-240

[whitebbking]

Cant find a section for power supplies... Hope it's ok to post here

I have a broken PSA-240 The regulator chip is labelled D313 E1L3... The previous owner replaced the 500ma fuse with a piece of wire, not surprising the regulator blew...

I had to replace with a LM7809CV.

Even with a 10k load, it's output is 12.6v

Any help on why it's outputting 12.6v from a 15v input would be appreciated.

*(The datasheet for the LM7809CV says it can handle up to 35v to produce 9v So I'm stumped....)

[cortezthekiller]

The D313 and the LM7908 are not the same components. I would imagine that the associated circuitry for the D313 are causing the regulated voltage to be elevated the few volts you are experiencing. Have you tried using a new D313 to see if the voltage returns to 9V?

[PRR]

Welcome.

> why it's outputting 12.6v from a 15v

The chip has a 2V-3V drop when not regulating. So that's what you expect.

The dumb-guess is that the 7809 ADJ pin is not tied to Ground. Not a shock since you don't know that the factory chip was same-as a LM7809.

In fact it seems that the (2S)D313 is a *transistor*, not a full regulator chip. There's more going on in there. The LM7809 is *not* a replacement. That it seems to give power is just random chance.

You could just ground the ADJ pin.

I fear it is not that simple.

As this seems to be an $11 wart, and funky failure *could* start a fire on your pedalboard, and it has already been abused an unknown amount, I'd bite the bullet and buy a new one.

[whitebbking]

It's not an $11 wallwart, it's a $50 Boss Power supply; A PSA-240 is genuine Boss



I cant find a D313 anywhere on the net including mouser. let alone a data sheet on it.... the PSA-120 has been the only guide I can use.... the PSA-120 is American input voltage and the PSA-240 is Australian input voltage..

I'm an idiot for assuming both the American and the Australian Power supplies would have an identical circuit after the transformer.

It is indeed easier to just walk away from this and cut my $1.40 loss. But it would be so nice to get it working... New direction is to alter the entire circuit and make it a "normal" regulated Supply.

[whitebbking]

Maybe it is a Sanyo 2SD313 (not that you can tell looking at the chip). I've asked my local supplier if they have any.

[slacker]

You could try and trace out the circuit and see if it looks the same as this http://mlb-d1-p.mlstatic.com/boss-psa-120-original-schematic-wiring-diagram-7596-MLB5238919360_102013-F.jpg if it is then maybe the diode (D5) has failed and the regulator is floating.

[whitebbking]

Rigtho.. Here's my attempt at the schematic.. Definately not a standard regulator circuit... I'll post more if I can get the 2SD313...

[PRR]

> my attempt at the schematic..

Far more likely like this:



which is a standard (and super-simple) regulator.

If BOSS asks $50 for that, they must be very proud of themselves.

The transistor is nothing magic. You need NPN. You need a tab-pack (for dissipation). Anything in a TO-220 is likely to be more than ample current and voltage. In the US, the TIP29 would be suitable and very available. TIP29A, B, C are the same for higher voltage-- you don't need the hi-spec ratings, but they will be fine.

I doubt the US and AUS versions differ past the plug and transformer. The transformer secondary is around 10V AC, and after that the wall-juice does not matter. (Actually the 50Hz power suggests a capacitor 6/5 the size needed for 60Hz power, but 470uFd is probably way-ample in either case, just a super-popular value.)

[duck_arse]

I've asked my local supplier if they have any.

who is your local supplier?

[if you was to say jaycar, you'd need to sub - eg mje3055, tip3055, tip31, tip41 - all appear in their cat, are all tab mounts, are all npn.]

[whitebbking]

Thanks for all the help.. Jaycar is my local supplier.. I'll organize this early next week.... Weekends is performance.. not maintenance

I'll let you know the outcome.

[chrisaxeman]

Know this is years old, but being an Aussie will add that I've come across differences in PSA-240's.

Opened one up today same as the OP's with a failed NPN as described (Date code is '97).

Years ago maybe 2003, opened another (bought from the same store)  which ran a 7809 with the usual small ceramic ripple cap across the output, as well a another in parallel with the main 1000uF filter cap, 4 x IN4007's for a rectifier bridge, no fuse, had a poly-switch protector in series with the either the output or +ve reg input (probably the latter), and I'm sure a ~14vac raw feed, not the ~12vac I measured today.

Be interesting to see if the one I pulled down years ago has a date code. Other than the higher parts count, don't know why the 7809 config wasn't the norm.