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A501 / Z501 Luxkit Amplifier schematic
A501 / Z501 Luxkit Amplifier schematic
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Old 15th March 2019, 08:45 AM   #91
SONDEKNZ is offline SONDEKNZ  New Zealand
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Default Bypassing OPAMP to test Power-up?

MOOLY

I'm very happy to try this.

Earlier in this thread you suggested bypassing the OPAMP simply by earthing LEG-7 to Chassis Ground. I never tried it.

Will this achieve the same thing? This would be easier to achieve for me.

It's just that I have been poking and prodding for quite a while, with my multimeter pin set in continuity mode. One LEG-5 and the other trying to find a resistor that is connected. No luck at all so far.

Will Chassis Grounding LEG-7 achieve the same thing?
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Old 15th March 2019, 08:55 AM   #92
Mooly is offline Mooly  United Kingdom
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A501 / Z501 Luxkit Amplifier schematic
Grounding pin 7 artificially pulls the servo output to zero volts which would allow the main amplifier to work conventionally.
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Old 15th March 2019, 09:10 AM   #93
SONDEKNZ is offline SONDEKNZ  New Zealand
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Default BYPASSING OPAMP (Short across LEG-5 and Associated Resistor)

MOOLY

I managed to find the resistor associated with LEG-5, using the CONTINUITY mode, as you described.

I attached a thin (white) wire to LEG-5 and to the other end of the Resistor knowing that this would leave the Resistor involved, as you prescribed.

(See Photo...)

I tried to power-up but the Protection Circuit still locked me out. No progress there.

I'm not sure what I have just proven, if anything...
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File Type: jpg LUXMAN LUXKIT Avance Z501 BYPASS OPAMP LEG-5.jpg (844.0 KB, 43 views)
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Old 15th March 2019, 09:33 AM   #94
SONDEKNZ is offline SONDEKNZ  New Zealand
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Default Did I grab the wrong leg?

Sorry MOOLY, I think I grabbed the wrong leg.
Tomorrow, Iíll move the wire to LEG-7 and try the test again.
That may change the outcome.
Iíll report the results.
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Old 15th March 2019, 09:35 AM   #95
Mooly is offline Mooly  United Kingdom
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A501 / Z501 Luxkit Amplifier schematic
Does pin 7 of the opamp now read dead short to ground (with the amp off)? That is what we want.

Pin 5 doesn't go to ground directly, its the other end of the resistor connected to pin 5 that does.

Also measure the DC offset at the main amplifier output in this new condition.
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Old 15th March 2019, 09:36 AM   #96
Mooly is offline Mooly  United Kingdom
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A501 / Z501 Luxkit Amplifier schematic
Lol OK.
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Old 15th March 2019, 09:39 AM   #97
Mooly is offline Mooly  United Kingdom
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A501 / Z501 Luxkit Amplifier schematic
This pin to ground. Also be absolutely sure that you don't inadvertently touch pin 8 to ground as that would short the supply rail.

I'll look in later
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File Type: jpg {ED27D826-FA11-4EA9-ABFF-9C0CE42FB1E0}.png.jpg (164.8 KB, 37 views)
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Old 15th March 2019, 09:44 AM   #98
Mooly is offline Mooly  United Kingdom
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A501 / Z501 Luxkit Amplifier schematic
That board looks very crusty around the IC. If the amp performs OK with the shorting link then it might be worth giving the opamp and its pins a scrub with iso (alcohol), particularly on the pins 1 to 4 side. Don't be afraid of wetting the board and components with iso.

The input to the servo is high impedance and so easily affected by unwanted conductivity. The IC is still the last suspect in all this... yes it might be faulty but I certainly wouldn't bet on.
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Old 15th March 2019, 10:24 AM   #99
pitbul is offline pitbul
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My thinking was: that opam is easily available in electronic spare parts store and to me your location written in the sign confuses me. My thoughts were that in Auckland New Zeland there must be many such stores, or there is something wrong with my perception.
If you are on some island nearby, then I absolutely understand why this opam will travel few days, that is the point.
Ok, Mooly push it, I think he is novice to schematics and electronic parts, but as I can see he is doing very well. I have so many "friends" who says that they understand electricity (or electronics), but they will never be brave to do the repairs like SONDEKNZ. If he isn't so persistant, I would pull out, now I am interested on the result.
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Old 15th March 2019, 09:03 PM   #100
SONDEKNZ is offline SONDEKNZ  New Zealand
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Default Some more quick measurements...

MOOLY

I can see that I did attach my thin white wire to the wrong leg.

While in this condition - before I change the wire to LEG-7 - I have provided some more measurements, as you have requested.

Quote:
Does pin 7 of the opamp now read dead short to ground (with the amp off)? That is what we want.
There appears to be no CONTINUITY on my multimeter between LEG-7 and Chassis Ground.

Quote:
Pin 5 doesn't go to ground directly, its the other end of the resistor connected to pin 5 that does.
Yes. I understand that. That is why I connected the Resistor on the far side, so that the Resistor still stays involved in this little work-around.

Quote:
Also measure the DC offset at the main amplifier output in this new condition.
Checking DC OFFSET with the amp power ON: -
P1 (LEFT): .1 VDC (Perfect!)
P2 (RIGHT): 6.8VDC
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