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| Author: | karyoker [ Tue Nov 13, 2007 8:02 am ] |
| Post subject: | Power Supplies |
In reference to the DBX thread...Power supplies are not that hard to troulbleshoot. This applies to all power supplies.. this is a pic of the 266XL ..On the right is the transformer it converts 110 volts to a lower voltage. Check it with an ohm meter The primary (line input) should read about 1/2 ohm In my case it read infinity.. The secondary should read about 1 ohm. The little black guys close to the plug from the secondary are 4 diode rectifyers. They are checked with an ohm meter They should have a 10/1 ratio by reversing the meter leads across them Sometimes all 4 are in a single chip which can be checked the same way. 90% of the time a bad rectifier will be a dead short. In which case will blow the fuse or breaker. ( a rectifier converts alternating current to DC half wave the filters reduce the remaining AC components to nill) The round silver cans are the filters They are fairly inexpensive and usually replaced as a matter of caution. Next are the regulators The black square guys to the left A lot of audio stuff requires a positive and a negative voltage When bad they usually are a dead short. The output lead can be checked with a digital volt meter and should be very close to the reg voltage. Last but not least the resistance to ground on the output of the regs should be the several k ohms to make sure the load isnt shorted. All parts normally can be bought locally except for the power transformer at times. |
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| Author: | JoeChartreuse [ Fri Nov 30, 2007 12:03 am ] |
| Post subject: | Re: Power Supplies |
To check resistance of a component with an ohm meter, it must be taken out of circuit, or else you will get false readings through the board. This is accomplished by desoldering and removing one leg ( or one side) of the component from the board. Since diodes ( the four black things acting as a full wave rectifier) are inexpensive, you may as well replace them as long as you're desoldering them anyway. However, these are directional components, and must be put in with the indicator band facing the same as they were, or they will blow. I am not looking at a spec, but the "silver cans" may not be "filters" (capacitors- most of which have colored PVC sleaving in audio applications). They may well be a type of op amp,( active component) if they look like little hats, or have more than 2 or three leed soldered into a circuit. A good troubleshooter works with the "Locate, sectionalize, isolate" theory. Before poking around, you might wish to find a schematic/drawing online for your unit. On this document should be marked voltages throughout the board. Instead of desoldering anything, turn the unit on and follow the voltage (AC and DC) through the circuitry. Where it's right going in, but wrong coming out is probably where your problem lies. Before even doing that, inspect the boards components - and the board itself- for discoloration, (or on the board, possibly a shinier surface). This is usually caused by excessive heat, possibly indicating a burned out component. Then inspect the underside of the board. Here you check the silver lines ( lands and pads ) that make up the circuit connections on your board. Look for breaks, or lifting from the board, or discoloration ( possibly indicating that the component on the reverse side is burned out. If a land is cut or lifted, solder a piece of solid 24 gauge wire across the break. I can't give you a course in electronics in a post, but I hope this helps. |
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| Author: | jerry12x [ Sat Dec 01, 2007 8:43 am ] |
| Post subject: | Re: Power Supplies |
I am not looking at a spec, but the "silver cans" may not be "filters" (capacitors Yes, they are electrolytics. |
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