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Old 6th September 2013, 04:35 PM   #1
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Location: Windsor, Ontario
Default Power/Protect cycling

I have an American Bass amp here where the power was cycling between power and protect. When I first attach remote power, the relays would engage, and then click out. Then the amp would cycle between power and protect about every 2 seconds.

When I test between the main ground and the secondary ground, RCA shield, or inductors I get 1.49vdc pulses with the amp cycling.

I removed the output driver card. This in turn stopped the cycling. The amp powers up. Pulls no excessive current. PS waves look good. All voltages are present.

When I tested the pads where the driver card attaches, all the voltages look fine. However, when I touch the red probe to pads 3 or 6 of the first bank of the pads for the left side of the driver card, the amp will protect. It shows the voltage then into protect. A reset of the remote, amps back to normal. Its only doing this on the left side bank of pads. When I test the right side pads it doesn't protect...

Any ideas? I'm lost. Never had this happen before.

Last edited by Deadly Sones; 6th September 2013 at 04:49 PM.
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Old 6th September 2013, 04:38 PM   #2
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Make and model would be useful.
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Support for Flying Mole, Allen & Heath, Valve amps, older designs & 2CVs. www.jonsnell.co.uk
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Old 6th September 2013, 04:44 PM   #3
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American Bass VFL750.1. The output card in this amp is the 3S V20. The one with 4 driver ICs. Here is a pic of the output section.
Attached Images
File Type: jpg IMG_1680.jpg (964.2 KB, 71 views)

Last edited by Deadly Sones; 6th September 2013 at 05:03 PM.
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Old 6th September 2013, 06:19 PM   #4
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O.K. there might have been a lil solder remnants between 2 of the pads. All I did was brush the pads with acetone, look to see where those pads led to... which is the low side banks... checked all the transistors again, hooked power back up and now it doesn't kick into protect when I test pads 3 or 6.

SO, the problem is likely driver card somewhere? Or something in the circuit once its connected...

I have the following voltages on the pads: From left to right:

Pad 1: -82 - -85v
Pad 2: -115.7
Pad 3: 122.5
Pad 4: 0
Pad 5: 0
Pad 6: 123.3
Pad 7: 0
Pad 8: 0
Pad 9: -122.7
Pad 10: -83 tp -85
Pad 11: -127.6

Center
pad 1: 0.2v
pad 2: 14.9v
pad 3: 4.9
pad 4: 0
pad 5: 0
pad 6: -5.1
pad 7: -0.2

right bank of pads

pad 1: -127.9
pad 2: -82 to -85
pad 3: -115.7
pad 4: -123.3
pad 5: 0
pad 6: 0
pad 7: -123.2
pad 8: 0
pad 9: 0
pad 10: -127.5
pad 11: -82 to -85

What should I check next?
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Old 6th September 2013, 08:06 PM   #5
ultra is offline ultra  Greece
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Without the module on, do you have DC on the output terminals?

And when the amp kept cycling from green led to protect led (before you remove the module), are you sure your power supply did not drop below 9V ?

Didi you measure the DC on the output then?
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Old 7th September 2013, 04:52 AM   #6
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Re-check the voltage on the pins. The first and last bank of pins should be mirror images. Be careful with polarity.

Do you think the solder bridges were there when it was going into protect (with the driver board in the circuit)?

I'm going to email you a diagram to test the driver ICs.
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Old 7th September 2013, 02:43 PM   #7
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Ultra: With the output card removed I have no DC on the output terminals. The amp was connected to 10 batteries @ the time it started to do this, and my bench was around 12.5v. When I had the card installed, there was a flash of 0.1vdc on the output terminals between the relays clicking in and out. Then if I put the black probe on the main ground and the red probe on either the secondary center tap, RCA ground shield, or the small filter inductors I was getting a reading of 1.49 volt pulses as the amp cycled.
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Old 7th September 2013, 03:00 PM   #8
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Perry:

I sent you an email with the driver readings

The solder bridge was desoldering "crud" stuck in the flux from my removing the card. I did look well before removing it for any solder bridges. All I did was use a tooth brush with acetone to remove the flux and some small specks of solder in it. There might have been something in the area I over looked that got removed when I brushed the board.

I rechecked the pads today with card still removed. Things did change ( center bank pad 7). The left and right banks don't seem to be a perfect mirror with these amps. The AB 1100.1 I did awhile back was the same. The big change in the rail numbers I believe is input voltage is 14.4 instead of 12.5.

Left bank
1) -90 to -115v
2) -133.5
3) 144.9
4) 0.009
5) -0.003
6) 145.4
7) 0.009
8) -0.003
9) -147
10) -93 to -113v
11) -147.3

Center (major change to pad 7)

1) 0.228
2) 14.96
3) 4.98
4) 0.009
5) 0.009
6) -5.03
7) -1.5v? This was -0.2 volts yesterday.... if I leave probe on it slowly pulls toward 1v but I gave up @ -1.3v. O.K. not sure why, but if I check this with my canadian tire meter I get the -1.5v if I use fluke clamp meter I get the -0.2v. ???

right bank

1) -148.5
2) -91 to - 112v
3) -137.1
4) 148.7
5) 0.009
6) 0.004
7) -149
8) 0.009
9) -0.011
10) -149.8
11) -90 to -115

Last edited by Deadly Sones; 7th September 2013 at 03:25 PM.
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Old 7th September 2013, 03:40 PM   #9
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LB3 and RB4 are positive voltage. They should be near the negative rail, not the positive rail.
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Old 7th September 2013, 04:01 PM   #10
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Oops, yes RB4 is neg. It was in my first post above, I somehow missed typing it when I put the new voltages up. Its neg on my paper. I will recheck LB3 shortly...
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