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C-Audio RA3000 Amplifier in protect mode
C-Audio RA3000 Amplifier in protect mode
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Old 10th November 2017, 03:12 PM   #71
ChrisTech is offline ChrisTech  United Kingdom
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how about swapping out Q24?
DMOD is a diode on the circuit diagram you could check that also.
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Old 10th November 2017, 04:20 PM   #72
Devinder is offline Devinder  United Kingdom
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After Q24 swap still the same.

I couldn't find DMOD on the board, I'll take another look next time I'm with the amplifier.
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Old 10th November 2017, 05:40 PM   #73
ChrisTech is offline ChrisTech  United Kingdom
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Right here is my last stab at this.
Here are measured voltages in red now.
Q25 should be turned on by the voltage present at its base.
This then drops the voltage at the. Are of Q24 which in turn turns on Q24.
The voltage is then dropped across R68.
This will turn on Q45.

I would measure each side of R68
You could also remove Q45 and see what measurements you then get.
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Old 10th November 2017, 06:28 PM   #74
Devinder is offline Devinder  United Kingdom
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Quick question, where did you clip the negative probe when taking the measurements?

Just thought I'd double check that clipping it on the negative post on the speaker post is ok?
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Old 10th November 2017, 06:31 PM   #75
ChrisTech is offline ChrisTech  United Kingdom
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On the green wire to the speaker output but I get the same measurements off the case or the bottom of the 9.4v zener.
Make sure you are firm on with the probes especially as these things get dirty
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Old 10th November 2017, 06:44 PM   #76
Devinder is offline Devinder  United Kingdom
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Thank you for confirming.

Yes there were a couple of places where I had to scrape a components leg with a screw driver before I could take a reading.
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Old 11th November 2017, 09:27 AM   #77
amptech is offline amptech  Scotland
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Devinder, did you float the o/p the amplifiers out stage from the protection circuit to see if the protection circuit is working by itself?.. and work on things in stages.

The basic of amplifier repair is not to just start replacing parts and see if it will power back up, but to ensure each stage is working and correct things where needed.
The t03 mosfets there outer case is connected to the output of this amplifier.

Start at the input circuits then to the tail pairs/ vas stage and output stages..

See how you get on.
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Old 11th November 2017, 09:38 AM   #78
ChrisTech is offline ChrisTech  United Kingdom
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Yes it's been rounded down for quite a while now to the protection circuit. And in fact to the later half of the protection circuit. Voltages from a working amp are above in my post in red and Devinder has given voltages from his.
Other issues have been found along the way including input opamp, unhappy zener voltage in the amplifiers differential input stage supply.

The issue is in the area of Q24, Q25 from what can be seen.

Devinder, can you confirm the voltage across SOFTSTART which is across the mains so be careful! It is a resistor shown on the PSU page.
Also the voltage across R152 in the protection circuit.
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Old 12th November 2017, 07:16 PM   #79
Devinder is offline Devinder  United Kingdom
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I took some more measurements today but I forgot to measure across R68 and R152, I'll do that in the morning.

I'll also remove and check Q45 tomorrow.

Here are the measurements I took.
Click the image to open in full size.
At Z7 I'm getting 200mVAC but it seems to increase to 200mVC from 0.

At the soft start resistor I'm getting 3.5VAC.
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Old 13th November 2017, 08:45 AM   #80
Devinder is offline Devinder  United Kingdom
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R68, 197mVDC I'm also getting a bit of ac there, around 5mVAC
R152, 57mVDC

Quote:
Originally Posted by ChrisTech View Post
Right here is my last stab at this.
Here are measured voltages in red now.
Q25 should be turned on by the voltage present at its base.
This then drops the voltage at the. Are of Q24 which in turn turns on Q24.
The voltage is then dropped across R68.
This will turn on Q45.

I would measure each side of R68
You could also remove Q45 and see what measurements you then get.
I've removed Q45 and it seems ok via those checks I found to do. Would you like me to measure the voltages in the areas that are different to yours with Q45 removed?
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