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Old 17th August 2014, 11:28 PM   #1
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Default crunch pzi250.2

This amp came in with bad outputs.I replace them and drivers.If i let this amp idle for about 40sec the outputs i replace will get hot.I think i have a bias problem in that channel..someone had already try to repair this amp and give up.

good side
TIP36c
1: 0.186
2: -30.94
3: 0.153

TIP35c
1: 0.524
2: 31.01
3: 0.153

Bias transistoC1815
1: -0.756
2: 1.097
3: 0.123

Bad Side

TIP36c
1: 0.526
2: -30.94
3: 0.015

TIP35c
1: 0.056
2: 31.01
3: 0.018

Bias transistoC1815
1: -1.105
2: 1.146
3: 0.397
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Old 18th August 2014, 06:55 AM   #2
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Location: Louisiana
Are you sure that the bias transistor isn't defective? The Vbe of more than 1.5v is excessive.
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Old 18th August 2014, 12:01 PM   #3
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I don't think C1815 is the original bias transistors.I will change it.
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Old 18th August 2014, 10:46 PM   #4
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I drop a new C1815 in there no change.
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Old 18th August 2014, 11:18 PM   #5
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Location: Louisiana
With 1.5vb-e, the transistor should be saturated and the collector and emitter should have essentially the same voltage.

Are you sure that the bias transistor is supposed to be a transistor with an ECB configuration?

Amps that use the TIP35/36 often use a transistor like the MPSA06 or 2N4401.

Confirm that the collector and emitter of the bias transistor connects to the bases of the driver transistors.
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Old 18th August 2014, 11:57 PM   #6
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The emitter is connected to the base of the (A940) driver transistor through a 47 ohm resistor.The collector is connected the the base of (C2073) through a47 ohm resistor.
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Old 19th August 2014, 01:08 PM   #7
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Location: Louisiana
Short the bias transistor collector to emitter and confirm that the channel works normally except possibly a bit of crossover distortion.

Measure the voltage on the bias transistors with the black probe on the emitter and the red probe on the other two legs (no collector-emitter jumper).
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Old 20th August 2014, 10:43 PM   #8
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With the jumper in place the channel works ok.


With no jumper
Black probe on center pin of emitter resistor
emitter -1.144
collector 1.178
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Old 20th August 2014, 11:25 PM   #9
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Black probe on the emitter of the bias transistor, not the emitter resistor.
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Old 21st August 2014, 12:07 AM   #10
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This is before the transistors have time to heat up
emitter and collector 2.378
emitter and base 0.710

Last edited by ian33; 21st August 2014 at 12:09 AM.
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