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Phono Pre-amp fault
Phono Pre-amp fault
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Old 31st January 2018, 10:51 PM   #11
audiopip is offline audiopip  Australia
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Quote:
Originally Posted by Dunk02 View Post
I just resoldered all connections in the backside of the board. No change.
I have a temperature controlled out air gun. What temp should it be set for the lead free soldered SMT components?

Thanks for the offer. Iíll keep that ace up my sleeve for the moment ��
First check the through hole large components. In particular the input output sockets as they have high thermal mass and are subject to mechanical stress. And that TO220 package which I assume is the regulator, of course if this is disconnected both channels would dead.

If you so see any dodgy SMT soldering set your iron to 260C and just locally retouch the joint.
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Old 31st January 2018, 11:10 PM   #12
stocktrader200 is offline stocktrader200  Canada
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if you put signal on both inputs, you should see signal (on a scope or small speaker ) on pins 1 and 7 if the chips are dual op amps. pin 6 if they are singles. both channels should be the same amplitude.
where the signal disappears is where a bad component is.
be sure to use a 100uf cap to the small speaker from ground
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Old 31st January 2018, 11:14 PM   #13
Dunk02 is offline Dunk02  Australia
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I have now found that the original 9V 1A transformer power supply has failed due to blown thermal fuse on the primary winding (the secondary winding is intact) . Perhaps this was caused by a short in the amp that has something to do with the loss on an output channel?
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Old 31st January 2018, 11:16 PM   #14
Dunk02 is offline Dunk02  Australia
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Originally Posted by stocktrader200 View Post
if you put signal on both inputs, you should see signal (on a scope or small speaker ) on pins 1 and 7 if the chips are dual op amps. pin 6 if they are singles. both channels should be the same amplitude.
where the signal disappears is where a bad component is.
be sure to use a 100uf cap to the small speaker from ground
Thanks. Are there three opamps in this board?
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Old 31st January 2018, 11:49 PM   #15
kevinkr is offline kevinkr  United States
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Phono Pre-amp fault
Moved to analog source since this is a phono pre-amplifier. Many phono pre-amp mavens hang out here.
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Old 31st January 2018, 11:51 PM   #16
kevinkr is offline kevinkr  United States
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Phono Pre-amp fault
Quote:
Originally Posted by Dunk02 View Post
I have now found that the original 9V 1A transformer power supply has failed due to blown thermal fuse on the primary winding (the secondary winding is intact) . Perhaps this was caused by a short in the amp that has something to do with the loss on an output channel?
It could be related, but some additional trouble shooting is required. An op-amp with severe ESD damage might do this.
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Old 1st February 2018, 12:49 AM   #17
Dunk02 is offline Dunk02  Australia
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Using an infrared thermometer, no components are more than 1 degC from each other.
Anyone have a circuit diagram for this unit?
I traced the sinewave (1kHz, 30mA) to this pin but see no signal on any other pin.
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Old 1st February 2018, 12:55 AM   #18
Dunk02 is offline Dunk02  Australia
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Originally Posted by stocktrader200 View Post
if you put signal on both inputs, you should see signal (on a scope or small speaker ) on pins 1 and 7 if the chips are dual op amps. pin 6 if they are singles. both channels should be the same amplitude.
where the signal disappears is where a bad component is.
be sure to use a 100uf cap to the small speaker from ground
There are no markings in the chip to show which is pin 1.
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Old 1st February 2018, 08:44 AM   #19
Dunk02 is offline Dunk02  Australia
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Had another read on the web and have now done the following.
Applied dummy load to signal outputs.
Compared signal of the two op amps closest to the terminal on the board.
The one closest to the terminals is the right channel.
The Signal generator set to 1kHz, about 80mV rms.

First the left channel: 2.2v sinewave at pins 2, 3,4,6,7,8 (my numbering is from bottom right clockwise). Pin 1 0V, pin 5 4.7v

Right channel: 2.2v sinewave at pin 2. Pin 3, 160mV. Pin 4 and 5, 4.7V. Pin 6,7,8 2.2V. Pin 1 0V.

I have no training and little experience in electronics. Pretty much relying on my high school knowledge from many years ago, and a few years of tinkering.

I have read up on op amps but need help to interpret these results.

Last edited by Dunk02; 1st February 2018 at 09:04 AM.
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Old 1st February 2018, 10:13 AM   #20
atsirik is online now atsirik  Greece
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I guess it is a TS972ID dual opamp (datasheet for example in https://www.mouser.com/ds/2/389/ts971-957361.pdf ).
Correct numbering is always from bottomleft counterclockwise (that means that the red pin is pin3 - see p.3 of datasheet). This mean that pin 4 (your pin 1) is correct ground and pin 8 (your pin 5) is Vsupply (correctly 4.7 in your measurements). However I see that your measurements show signal on both opamps for left channel and only one channel for right channel (which seems to be clipping unlike the other channel). How do you check inputs/outputs, with a scope? The 2 opamp outputs are pins 1 (your 4) and pins 7 (your 6). Do they show sinewave output?
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