(Continued from Part 1) With the unit unplugged, check the power supply section for bad solder connections. This may require that the unit be placed on it’s side and the bottom panel(s) be removed to give access to the Solder Side of the printed circuit boards. At the factory, a ‘Dip-Weave’ soldering machine was used to solder all of the components in place at one time. This can sometimes result in connections that, after time, the expansion & contraction of the circuit board(s) can have many bad connections resulting in failure, and could be a big pain in trying to find. If you have a magnifying glass that has a good high power, you can get a big close-up of a bad connection. You will note that a component wire and the solder pad it’s soldered to. A ring may appear to be around this component lead and could very well be a bad connection. Re-soldering it is a must. Add just a little fresh solder to it with a hot soldering iron. This may be required for a lot of connections. I have found over the years that (in most cases) this will cure 90% of the problem(s) that the customer (or you) is / are having with the unit. Seldom, you will have a component failure unless the unit was dropped, hit, water damage or not being connected to other equipment properly. Once all the above is done, but the unit still doesn’t want to power up, with the unit plugged in, take your multimeter, set it for DC Volts, 250 volt scale. Measure the voltage across the big Electrolytic Capacitors in the power supply section. Do not touch anything else. Your meter should read very close to the voltage printed on that capacitor. Note the polarity. Most power supplies will have two of these. One being the Positive leg and the other being the Negative leg of the power supply feeding the Audio Output circuits. If the DC voltage cannot be found across the capacitors and you know the power is on, there may be a bad rectifire or full wave bridge unit. This can be checked with the meter set on AC Volts, 250 volt scale. Check the input to the bridge. There may be 2 or 3 bridges in the unit. Look carefully at the biggest bridge and note the markings on the package. This will determine where you want to place your leads for exact measurement. If the bridge has no output, replace it with one of the same ratings (or better) to insure lasting performance. If the original part calls for a 400 Volts @ 4 Amps, use a higher rating like 400 Volts at 6 or 8 Amps. This will insure that it will not fail again, as the factory will under-rate parts in order to save money in production. Some newer equipment will utilize a ‘Switching Power Supply’ as found in most computers. This type of supply rectifies the current right off of the power cord and feeds it to a network that sends it to seperate filters and regulators to obtain the voltages desired. If this is what your unit has, you can troubleshoot it in the same manner, as I’ve seen many switching supplies with bad solder connections. If anything fails in a switching supply, it’s the high voltage and current Transistor that is under rated and should be replaced with a better one. If the original calls for a 400 volt @ 8 amps, use a 500 (or better) volt @ 10 amps. Thisc will insure that it will not fail again. The main bridge rectifier will sometimes fail, too, and should be replaced with a better unit as well. After all this, you should be able to get the unit to at least come on. Never turn up the volume control on any amplifier or receiver without proper speaker(s) connected. If no sound comes from the unit, you will have to ‘walk backwards’ from the speaker to inside the unit. Most of the newer equipment will have an output amplifire chip that ‘does it all’ in one package. These chips will fail, but very rare. Here’s a simple ‘click’ test that you can do to see if any speaker is good or bad: Take a D size battery and connect it to the speaker terminals. You will hear good clicks as you connect the battery to the speaker. A few good clicks will tell you right away that you have a good speaker. Check the wire that you are using to insure that it is free from kinks, nicks or abrasions, as this could effect the quality of your sound. This will be continued in Part 3 of this series.
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