Phonic 740 Powerpod Plus 2X220 Eats fuses

[Chaffeekid]

Ok Guys, bought this item on E-Bay, looks like brand new, inside looks great can detect no release of magic smoke No smell of anything burned or anything like that. The two 8 amp fuses on the power supply board pop upon turning the unit on.
The front panel lights up and the level indicator LED's show that a signal is getting through but no output, course that is because the fuses are toast.

I don't have a schematic for this unit, so really don't know where to start, thought about unplugging the main amp board to see if it still blows fuses, but haven't done anything but watch it blow fuses so far

Any help would be appreciated and a schematic would really help, I can send pictures if that would help. Hey I picked it up for 20.00 plus shipping so if I can get it going think I can make a profit

Thanks, Jim
MGySgt USMC (r)

[Chaffeekid]

Ok one other thing, I am an Amateur Radio (Ham) and am familiar with electronics to a degree, have built a couple of radios and with Enzo's, and others help on here have restored an old TNT 100 Peavey Bass amp for the Church and it is still working FINE.

Just my bona fides.
Jim

[The Dude]

I've never been inside one of these, so I can't help much. I'd look for the usual suspects- shorted output devices, etc. You might also try their support page and ask them for a schematic if you need one.

Submit a ticket - Powered by Phonic Help Desk Software

[mozwell]

This may help

[Chaffeekid]

Thanks Dude, (hey loved that movie), and Mozwell, looked at all the power supply schematics and could not find one that looks any where near mine? Mine has two 8 amp fuses, none I could find on the schematics specified 8 amps nor did I find one with two fuses in the plus and minus legs of the supply.

Filed a ticket with phonic via the link from Dude, so will see what they come up with. BTW, the serial number of the unit is BAU1J20737, I'm going to get this thing motivating or make it my life's work

[Jazz P Bass]

Is there a board designation for the 2 fuses silkscreened on the actual board?
The ones that I found where marked 1 amp.
Someone may have slipped you a 'mickie' & tried to repair the unit by installing 8 amp fuses.

If your amp is similar to the one that Moz posted, please be aware that the power supply is a Switch Mode device.
You must be extremely careful when testing any voltages.
The primary side is connected directly to the mains.

[J M Fahey]

Maybe I'm under a wrong impression ,if so forgive me, but if you think you'll repair the unit by fitting the proper fuses .... it does not work that way

If they blow (and replacements continue to do so), there is something else which makes them do that.

If I were a retired boxer trying to refresh it, I wouldn't start practicing with Mike Tyson

Same here, this is a very complex and dangerous amp.

Since it cost $20 up front anyway, I'd leave it aside for a while, say it in your meanest tone: "I'll be back !!! " and for the next few projects , keep practicing with more "normal" stuff, such as Peavey (a favorite), Crate, Fender, etc. amps which you can still get for peanuts at garage sales and such.

And then,when you grow up muscle, go punch that Tyson guy in the nose !!!!
I mean, the PowerPod

[Chaffeekid]

Ok, a little more information, it is NOT a switching power supply. It has a BIG transformer that makes up half of the weight of the unit. It has at least one ic 7812, a 12 volt positive power regulator, another one is hidden will have to remove it to check, I am assuming that it is on the negative leg of the power supply. I suspect that one or maybe both of these have went south. I have removed the power supply circuit board. And will be removing the two power regulator chips to check them. Any info on checking these IC's would be helpful.

And Hey Juan, I have worked with the old analog TV's both those with switching power supply's and transformers, yeah, they are all dangerous some even when unplugged, Those Caps can ZAP! So I think I'll throw a left hook followed by a right cross, used to take out the sailors

Jim

[Chaffeekid]

Hey and Jazz P Bass, (I have a Fender P Bass right out of the 60's) Beautiful Cobalt blue, has the cover over the split pickups and the ashtray cover over the bridge, a thumb rest above the 4th string, really sounds nice, love to play it although I am not that good
And yes it is silk screened T 8A for both fuses, (they were ceramic) there are 3 other fuses that are labled T 2A and they are ceramic also. I have checked all the diodes and cannot find any that are shorted or open, no burned resistors, so going to pull both of the power regulators and see if I can find out if they are the problem.
Jim

[Chaffeekid]

Ok, so I'm wrong again It does have a switching power supply. After careful study of the schematics that Mozwell sent, I have to admit that I was WRONG. So, what to do now, there are several rectifiers of the B823N20D variety, an L7915 and L7815 Plus and Minus, a 7812 and a 7805.
I removed the connectors from the switching power supply from the board which contains the 7805 and the 7812 psb, (Front Panel which lights up nicely). This board contains the two 8 amp fuses, which I have changed to 5 amps, less chance of smoking something.
When I turn it on without the switching power connected, no blown fuses. So I have surmised that the switching power supply/amp board is the problem, and I am going to rebuild it by replacing all the discrete components, yeah I know shotgun approach. I don't have a scope, only a volt/ohm meter, and all the discrete components are only about 30 bucks from Mouser, that will mean I have 50 bucks tied up in the unit, then if it doesn't work. Oh well sure will give me some entertainment with my de-soldering/soldering iron for a couple of days, hey at 70 years old I'm easily entertained
Anyone have any thoughts
Talking to myself again
Jim

[g1]

No, I think you were right. SMPS will not have any heavy transformer, and if it was disconnected you would not have any lights anywhere or power anywhere.
So it is probably the amp circuitry you have disconnected.

[J M Fahey]

used to take out the sailors

So what Service are you veteran from?

[g1]

So what Service are you veteran from?

I'm thinking grunt?

[The Dude]

... I'd look for the usual suspects- shorted output devices...

...

[Chaffeekid]

Juan, you didn't look at my signature in the first post. USMC Uncle Sams Misguided Children, or Uncle Sams Motorcycle Club, but probably better known as United States Marines, was in for 30 years 61 to 91, dabbled in a little bit of everything. Yep g-one, was with the 3rd Bn 5th Marines, 2nd Bn 3rd Marines, 1st Bn 7th Marines, Cuba during the Cuban Missile Crisis, far east service 3 times, still have all my limbs, fingers and toes, no additional holes, other than those performed by doctors, and about half of my brain left

Yeah, g-one, I keep reconsidering this, the front panel all lights up, the transformer weighs about 10 lbs the whole unit weighs around 20 something. I've ordered the output devices, B23N20D (4) a bunch of 2n5401's (10) a TIP31C and a couple of other small devices, the zener diodes seem to be ok.

And the schematics that Moswell hooked me up with don't match what is silk screened on the boards as far as components, nor does the header connectors on the board. Where the schematic shows a 6 pin connector, mine has only 4, as in the physical plug. So I think mine an earlier or possibly later version of the 740 plus.

Anyhoo, just waiting now for Mouser to send the components. Also am replacing the power regulators, 7805, 7812, 7915 and 7815, they are cheep and fun to take out and replace.

Hey keep those suggestions coming and I'll let you know if I get this thing working or throw it in the junk pile
Jim