I'm looking at a Zed Audio Gladius that won't power up. Its using a TL494. Board is mostly SMD components but looks fairly classic AB style, like a Gen X or Nakamichi etc.
TL494
1: 0.015
2: 4.66
3: 0.061
4: 0.436
5: 1.506
6: 3.514
7: 0
8: 0.070
9: 0
10: 0
11: 0.008
12: 13.48
13: 5.01
14: 5.01
15: 5.01
16: 0.254
Photo coming next since this might be fairly new Zed and kind of rare?
TL494
1: 0.015
2: 4.66
3: 0.061
4: 0.436
5: 1.506
6: 3.514
7: 0
8: 0.070
9: 0
10: 0
11: 0.008
12: 13.48
13: 5.01
14: 5.01
15: 5.01
16: 0.254
Photo coming next since this might be fairly new Zed and kind of rare?
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Thanks I've sent him a message.
Otherwise, nothing pops out at me as being an issue with this amp. No shorts. Also no LEDs (Power/Prot) are lighting. The only thing I can say is for a brief 1/10th second at startup my PS barely blips off 0.005A, to about 0.020A then back to 0.005A but that could just be caps charging.
Otherwise, nothing pops out at me as being an issue with this amp. No shorts. Also no LEDs (Power/Prot) are lighting. The only thing I can say is for a brief 1/10th second at startup my PS barely blips off 0.005A, to about 0.020A then back to 0.005A but that could just be caps charging.
While possibly waiting for Mr Mantz to respond; I put this one back in front of me.
Updated readings on the TL494, now showing momentary event at first application of all power terminals:
TL494
1: 0.015
2: 4.66
3: 4.78 --> 0.061 after .5 seconds
4: 0.872 --> 0.436 after .5 seconds
5: 1.506
6: 3.514
7: 0
8: 0.070
9: 0
10: 0
11: 0.008
12: 13.48
13: 5.01
14: 5.01
15: 5.01
16: 10.37 --> 0.254 after .5 seconds
I started 'snooping' around this amp. Found a bunch of BurBrown opamps! Cool.
And then I found a few faults.
Q1/Q2 are PS FET drivers. They're B631K PNP, and they're both shorted collector-base out of circuit.
Datasheet
SSCLS02472-1.pdf
Also, R14 and R15 are blown open. 20 ohm resistors.
There are no NPN drivers in this amp from what I can tell.
Updated readings on the TL494, now showing momentary event at first application of all power terminals:
TL494
1: 0.015
2: 4.66
3: 4.78 --> 0.061 after .5 seconds
4: 0.872 --> 0.436 after .5 seconds
5: 1.506
6: 3.514
7: 0
8: 0.070
9: 0
10: 0
11: 0.008
12: 13.48
13: 5.01
14: 5.01
15: 5.01
16: 10.37 --> 0.254 after .5 seconds
I started 'snooping' around this amp. Found a bunch of BurBrown opamps! Cool.
And then I found a few faults.
Q1/Q2 are PS FET drivers. They're B631K PNP, and they're both shorted collector-base out of circuit.
Datasheet
SSCLS02472-1.pdf
Also, R14 and R15 are blown open. 20 ohm resistors.
There are no NPN drivers in this amp from what I can tell.
Attachments
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Zed calls it "Pulse drive" on the board.
With Q1 & Q2 removed, the amp takes some power. The power LED comes on and stays on. I'll work on this one more tomorrow 🙂
With Q1 & Q2 removed, the amp takes some power. The power LED comes on and stays on. I'll work on this one more tomorrow 🙂
The drive appears to be similar to that used by MTX.
The emitters of the internal drivers of the 494 are grounded. Pins 8 and 11 drive the PNP driver transistors.
Which terminals of the PS FETs connect to the transformer?
The emitters of the internal drivers of the 494 are grounded. Pins 8 and 11 drive the PNP driver transistors.
Which terminals of the PS FETs connect to the transformer?
Do you believe that these are the only problems?
Do you want to try an alternate driver transistor to continue testing?
Do you want to try an alternate driver transistor to continue testing?
I've got some B631K I could try for now. I don't have any SMD 20 ohm but I do have some 1/4w 22 ohm I could try out also. Definitely need to order parts once all faults are figured out.
In the meantime before I put good B631K back in for further testing;
TL494 without the drivers
1: 1.600
2: 3.035
3: 0.063
4: 0.393
5: 1.509
6: 3.518
7: 0.001
8: 10.37
9: 0.001
10: 0.001
11: -0.048
12: 13.34
13: 5.01
14: 5.01
15: 5.01
16: 0.254
It may be weird that pin 11 is negative. Pin 8 & 11 are driving?
In the meantime before I put good B631K back in for further testing;
TL494 without the drivers
1: 1.600
2: 3.035
3: 0.063
4: 0.393
5: 1.509
6: 3.518
7: 0.001
8: 10.37
9: 0.001
10: 0.001
11: -0.048
12: 13.34
13: 5.01
14: 5.01
15: 5.01
16: 0.254
It may be weird that pin 11 is negative. Pin 8 & 11 are driving?
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It is on DC coupling. I'm using channel 2 of the scope set to DC for those images. Channel 1 isn't hooked up nor displaying. The scope is aligned at 0 with nothing connected.
I only use AC sometimes when testing outputs at the terminals etc because sometimes DC coupling seems to create noise on the amplifiers.
I only use AC sometimes when testing outputs at the terminals etc because sometimes DC coupling seems to create noise on the amplifiers.
Do you see any difference in the drive circuit components or any out-of tolerance parts (the 22 ohm resistors are OK)?
Confirm that you read the same resistance between the terminals of each of the parts for both halves of the drive circuit.
Confirm that you read the same resistance between the terminals of each of the parts for both halves of the drive circuit.
With temporary 22 ohm resistors I felt confident enough to install good parts B631K drivers.
The amp powers up completely now with about ~61vDC rail.
Seems like this one is on it's way to live another day, once I receive correct parts order.
The amp powers up completely now with about ~61vDC rail.
Seems like this one is on it's way to live another day, once I receive correct parts order.
Both pin 8 & 11 look like this. Channel 2 again. Probe this time is set to 10x because trace was going off the screen at 5vDiv at 1x.
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OK. I didn't trust it when they were so different but if they're the same, I don't see a problem.