The power supply was shorted out on secondary side. now only puts out 6.5 volts intead of 13.8?
can anybody put me in the right direction?
thank you Glenn.
gcamara@cox.net
Hi Glenn
I couldn`t find anything on google about the Pyramid 14g.
If we assume it is a transformer type power supply with one output, you may have damaged either a diode (opened) or a resistor in line with the B+ lead.
Your mutimeter may also be damaged, although only the amp measuring circuits should be affected. Measure the output with another VOLT meter.
Since the fuses do not seem to have blown, your transformer should still be ok.
If you are hearing a louder than normal humming sound from the transformer, it is under overload from a possible shorted diode.
Don`t run it this way, until the short is located in the circuit.
Posted on Feb 14, 2008
OK Glenn
A power diode can be tested in circuit. A resistor most of the time you can get a ballpark figure to decide if it needs replacing. You have to know color coding first.
In your case I would just look for a burned or cracked looking resistor.
Make sure you are unplugged from AC.
The power diodes are likely a unit with four diodes in it configured as a bridge circuit. This may be a black rectangle about 1,5 x 1 x 1/4 inch in size. It would have 4 leads coming from it soldered to the pc board. On the side of it may be diode symbols.Your multimeter can detect a dead short across any two of the leads.
Its not necessary to test the diodes unless the transformer was humming.
a B+ lead is just the red positive power connection to whatever you are connecting the power supply to.
Don`t go any further than this without a hands on tech. helper.
Hi Glenn
The 4 diodes are your bridge circuit. Yours happen to be separate units instead of being put in one package with four leads.
Diodes are tested in two directions by reversing the ohm meter leads. A good digital multimeter should have a diode function in the switch. Read the manual on how to use this.
A picture would be helpful. see if you can it add to this thread. The link at the top of the page, just goes to your profile.
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Hi.
It very unlikely the voltage went down. I think you should re measure what the voltage should be yes it 13 volt is after the bridge you wil get this with dual 6.5 volt ac from the transformer, they don't change voltage unless you have a short at the output, and if you did you will blow the transformer, is your reading from 2 wires or is it three wires, output, the center to the end should be 6.5 and end to end maybe 13.8.
I would need to see the schematic to know what voltage you should be getting.
I wouldn't look on a bat transformer but ether, bad bridge or wireing.
I hope this help's
What About Bob
Posted on Feb 14, 2008
Hi,
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hello no parts were changed. a friend was over and put the red lead from my multimeter into the 10 amp max unfused hole on my meter then checked the output volts on the power supply the power supply started beeping right away and then it only put out 6.5 volts
eagle2
thank you for the info.
is there a way to test the diode with a multimeter while still on board?
also is there a way of testing a resister still on the board?
and also what do you mean by the b+ lead?
i see most things inside are listed with a r,d,c,z
thank you Glenn
hell after looking at this several times i can not see any resisters that look burnt out or cracked.
I can see a bank of 4 diodes in a row near were the output power leads come from. but what i see is the diodes all have just 2 legs on them.
all diodes do not have continuity going throught them.
all but 2 resisters do not have cont. the other 2 do have cont. my e-mail is on the top of the page if you woulde like to e-mail me i can send you a picture of the board if that might help understand. thank you Glenn..
gcamara@cox.net
I tried to add a link to this i'm not sure how to so i added my email address. thanks Glenn
Where any parts changed? What was the cause of the short?
you will need more info, schematic, if the voltage has change, you will have to find were the source is from inside the amp, look for burt transistor, resistors, it is most likely it is comming form a voltage regulator that has a 20 volt input and a 12 volt output. Source could also be comming from a IC, multiple voltage output.... sence I don't have all info or , model, schematic , just look for burt parts.... over 50% will show witch part is burt. Also , some or defficule to test the output, without load the voltage may be lower or change if is has a Ic regulation design were at no load , it's custent voltage reading shut down it's driver withing inside the ic (voltage regulator intergrated circuit), I also seen with over load , the voltage would drup down to lower voltage... this is over current protection or that the source were it supplys the voltage can't give the output that is half shorted enough voltage because it is draning it down.gatultlvt;e to testulais your
you will need more info, schematic, if the voltage has change, you will have to find were the source is from inside the amp, look for burt transistor, resistors, it is most likely it is comming form a voltage regulator that has a 20 volt input and a 12 volt output. Source could also be comming from a IC, multiple voltage output.... sence I don't have all info or , model, schematic , just look for burt parts.... over 50% will show witch part is burt. Also , some or defficule to test the output, without load the voltage may be lower or change if is has a Ic regulation design were at no load , it's custent voltage reading shut down it's driver withing inside the ic (voltage regulator intergrated circuit), I also seen with over load , the voltage would drup down to lower voltage... this is over current protection or that the source were it supplys the voltage can't give the output that is half shorted enough voltage because it is draning it down.gatultlvt;e to testulais your
start by disconnection the source out and them messure it, then re mesure it with load in... keep in mind, also if the multimeter is half as good as testing any curcuit.... this won't help you with messurment. I know I'm not helping you lots... it is just that I don't have enough info to answer you, just an outlook were the problem may be. Poer supply is very easy to repair.... time is another issue it may take several hrs to figure it if you don't have a schematic to show were the problem can be. Regards
start by disconnection the source out and them messure it, then re mesure it with load in... keep in mind, also if the multimeter is half as good as testing any curcuit.... this won't help you with messurment. I know I'm not helping you lots... it is just that I don't have enough info to answer you, just an outlook were the problem may be. Poer supply is very easy to repair.... time is another issue it may take several hrs to figure it if you don't have a schematic to show were the problem can be. Regards
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