I'm working on a Memphis amp. It powers up fine, and draws <1A current. With the driver boards in, I get ~58vDC on the speaker terminals. If I pull the boards, I have 0vDC, as one would expect. I removed the output transistors and have found one particular waveform that seems to 'follow' me. I used the center tap for reference, and probed around a bit.
I found this waveform or one very similar to it (e.g. slightly 'sharper' corners, but essentially the same frequency and amplitude), in locations such as:
-The output transistor pins holes
-Pins 4/9/11 of LM361 (all three had the same waveform)
-When probing the MC14093BCP (Unfortunately do not remember the exact pin, somewhere in the middle of the second set of pins so maybe 9-11)
-The middle leg of the D55-58, outer ones were the same wave with a slightly higher amplitude
Does this stand out as meaning anything to you?
I found this waveform or one very similar to it (e.g. slightly 'sharper' corners, but essentially the same frequency and amplitude), in locations such as:
-The output transistor pins holes
-Pins 4/9/11 of LM361 (all three had the same waveform)
-When probing the MC14093BCP (Unfortunately do not remember the exact pin, somewhere in the middle of the second set of pins so maybe 9-11)
-The middle leg of the D55-58, outer ones were the same wave with a slightly higher amplitude
Does this stand out as meaning anything to you?
Attachments
Upon further testing, I read the "Generic Class D 1" section of the repair guide again. I found one of the TL074C(N) to have close to 14v-15vDC on all pins except 8. Neither have the triangular waveform shown on pin 5. The second of the two TL074's only has ~7v on pin 6, if that matters any.
Edit 1: OK, digging further I only have .85v going to the 'power board' (with the F16/B52 on it). I've got to dig into why this further before anything more can be said for IC's, I assume.
Edit 1: OK, digging further I only have .85v going to the 'power board' (with the F16/B52 on it). I've got to dig into why this further before anything more can be said for IC's, I assume.
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OK, by replacing the F16/oscillator, the crystal is once again oscillating, and the LM361/B52's Pin 4 is looking normal, triangle wave and all. However, the Pin 3 is about -12v (only with the two driver cards in, without them it has nothing), and pin 9 and 11 are -2v and +3v respectively. Is this indicative of a bad LM361, or perhaps bad components on these driver boards? I'm trying to stumble my way through a few repairs here, but some things I could absolutely use firsthand suggestions on. The main issue is still straight DC coming from the speaker terminals. The FETs are at around 55v, straight DC only, on all three legs (but not exactly the same) and did not test to be blown.
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