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Old 9th September 2006, 02:57 AM   #11
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If any of the power supply transistors are getting hot when the rectifiers are out, there may be a problem with the drive circuit. This is when a scope is very nice to have. You can look at the waveform and determine if there is a problem.

You're right, the removal of the rectifiers broke the connection to the audio section. The problem is very likely in the audio section.

Are you 100% sure that you have the caps installed properly?

You need to buy a current limiter. An H6054 headlamp will work. Use the high beam connections. Insert it in place of the fuse.

With the limiter in place, power up the amp and measure the voltage across each of the emitter resistors. There should essentially be no voltage across the resistor. 0.001 volt is common. If you find some that are 0.05 (for example) and the rest are essentially at zero volts, that will tell you where excessive current is flowing.
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Old 9th September 2006, 03:47 AM   #12
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I will most deffinately check the caps again , But I know now that the square solder points are positive and round negative thats how i have them soldered in , the pic you have of the caps is exactly the same layout on my 280, I did check to see if the the powersupply transistors were getting hot or even warm and they werent they stayed very cool, by chance can you post a pic of the rectifier sections , I want to make sure I have them in the right order , right after the last powersupply transistor I have the FEP16CT then after that the LM340T15 per side .

also are they dual - or dual + I only ask to check and see if anyone else may have replaced wrong parts in the amp and i just followed them , the FEP16CT's are dual + , originally after the FEP16CT a L7815CV was used but the recomended cross reference was to use the LM340T15 hopefully this is ok.

I will test the Emitter resisotrs asap

thank you
redblaze
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Old 9th September 2006, 05:25 AM   #13
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These are from a 225. The photos of the 275 have the clamps covering the components.
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Old 9th September 2006, 05:27 AM   #14
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This is the other side. The number on the transistor (that's too light to read) is 2n6491.
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Old 9th September 2006, 05:34 AM   #15
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well I decided to test putting 1 rectifier in at a time and test the amp , I have 1 channel working , if you are looking at the amp RCA's facing to you the right side is the side that is working and also has the power light , the powersupply quit screeching aswell , if i put the other rectifier back in and remove all outputs on the left side replacing them 1 by 1 and testing the amp will that work to pinpoint the bad parts aswell ?
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Old 9th September 2006, 05:50 AM   #16
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Both rectifiers must be in place for either channel to operate properly.

To make sure that there is no confusion, the rectifiers are the components with the diode symbols.

The 2n6488 and 2n6491 next to the rectifiers are the regulators. I'm not sure why you have 340t15 regulators. If the board looks precisely like the 225, the components should be the 88 and 91.

If an output is defective, it should be easy to find with an ohm meter.

Have you checked to see if any of the outputs are shorted?
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Old 9th September 2006, 06:36 AM   #17
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I just did , none of the outputs are shorted but I pulled them from the board again to test them , I will replace them and see if when I test them installed I get a short. per side if you start from powersupply to front of the amp on 1 side you have 5 IRF2807 then the FEP16CT , the LM340T15, 3 2N6488 (in this case the D613 replaced the 6488's) a 1 inch space then 3 2N6491's
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Old 9th September 2006, 07:07 AM   #18
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Can you make a voltage measurement?

Amp on
DC volts
Black lead where indicated in the photo
Red lead on pins 4 and 8

Pin 8 should have positive 15 volts (approximately). Pin 4 should have negative 15 volts.

If that's not what you have, turn the amp off and measure the resistance between pin 8 and the third leg of the 2n6488 next to the rectifier (as shown in the previous photo). Do the same between pin 4 and the third leg of the 2n6491. Both should read ~0 ohms.

The lm340 regulators are both positive regulators. From the description of the parts layout, your amp seems to be exactly like the amp I have here and there should be no lm340 regulators.
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Old 9th September 2006, 07:32 AM   #19
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on this 280GX on 1 side you have your powersupply transistors then 1 FEP16CT originally there was a L7815CV but when the guy at Parts Electronics looked it up the part it referred was the LM340T15 to take the place of the L7815CV, is this correct or should i pull the LM's and get better parts ?
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Old 9th September 2006, 07:45 AM   #20
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I just tested the L7815CV's and they tested ok so I put those back in and the amp still did the same thing well I will let it go for tonite and start over tomorrow , I wil do everything you told me to do earlier checking the Emitter resistors, I will try to get a good camera to take a pic of the board layout I have , the power supply and 6 capacitors in the center of the amp look the same as the 275 but moving to the RCA section it starts to get much different aswell as the transistor layout .

I do greatly appreciate your help
redblaze
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