Dragster DB 505 5 channel amp - diyAudio
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Old 18th September 2011, 11:49 AM   #1
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Default Dragster DB 505 5 channel amp

Got this amp, and it was in protection mode. So i had a quick check and one of the output transistors was bad. Changed it for the same thing and powerd the amp again. Still red led on. So i checked if the SG3525 was working. It wasnt. I traced the PCB and found that a transistor (Q45) was bad. Changed that and also the SG3525. Now if powered up, the SG has VCC voltages and also 5V on legs 11 and 14. Checked with a scope, its a squarewave. After that measured the power FETs, pin 1 has that 5VDC square, pin 2 has 12VDC and pin3 is 0VDC. None of them seems to be shorted and all four have the same parameters. So something is happening, but still the red led is on, and no sound comes out from the amp. The output transistors have +/- 22VDC . A bit small or is it normal? Nothing heats up or anything. Any ideas? Maybe a schematic? Mr. Perry for shure has some ideas i hope.
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Old 18th September 2011, 12:36 PM   #2
timwebb is offline timwebb  United States
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got a pic of the amp?
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Old 18th September 2011, 12:50 PM   #3
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Its pretty much like that one DSC00158 | Flickr - Photo Sharing!
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Old 18th September 2011, 09:07 PM   #4
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If you drive an audio signal into the amp and trace it with the scope, where does it stop?

Do you have both positive and negative supply voltage on the op-amps in the preamp section?
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Old 21st September 2011, 06:24 PM   #5
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Both positive and negative voltages are ok. It uses ST 074C chips in preamp. Without the schematic, its pretty impossible to trace the signal on a 2 layer PCB. All the 4 chip outputs(074C pin 1,7,8,14) have the signal that i feed from the signal generator. Then i can trace some resistors and capacitors and then who knows where it goes, but near the output i picked the signal up again and it goes to a chip "15532" where the signal looks a bit like a squarewave instead of the sine i use.

A quick question from a friend - sinuslive SLA-1500. Says that one of the capacitors in the main power supply (C63) has a voltage of about 60VDC on it, but when he connects the subwoofer, the voltage will be about 100VDC, if speaker disconnected, voltage again normal, 60VDC. The other capacitor (C67) has always about 60VDC, no matter if the speaker gets connected or disconnected.
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Old 21st September 2011, 08:15 PM   #6
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Can you post a photo of the area around the 15532 IC?

Maybe one of the capacitors is open or out of tolerance. IF you have any more questions for the SL amp, start a new thread.
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Old 24th September 2011, 08:10 AM   #7
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Some pictures finally. If its that chip http://www.datasheetcatalog.org/data...hm/ba15532.pdf then it seems that the VCC is missing.
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Old 24th September 2011, 08:53 AM   #8
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What DC voltage do you have on the terminals of Q42?
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Old 24th September 2011, 03:09 PM   #9
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Measured from GND Q42 and the results where :
Pin1: 13,0 VDC
Pin2: 12,3VDC
Pin3: 12,3VDC

Also cheked the nearby Q41 and:
Pin1: -13,0 VDC
Pin2: -12,3VDC
Pin3: -12,3VDC

Also that 15532 thing:
All pins show 0VDC if measured from GND.
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Old 24th September 2011, 05:47 PM   #10
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The amp may have an isolated secondary ground. If that's true, you have to use a secondary ground point (non-bridging speaker terminals or the secondary center-tap) as a reference (black probe).

You stated that you didn't have negative supply voltage on pin 4 of the 5532s. Do you have positive supply voltage on pin 8?
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