Technics Amp Need help to find an equvilent transistor

Thread Starter

DarkV

Joined Oct 14, 2022
9
Hello, I have a Technics amp that cuts out due to a bad fan (a common fault), I have to replace the fan with a working unit, but one of the drive transistors is faulty as the fan works then stop the protection and cuts in. Works perfectly on low volume. It is
2SA1530A. All ones listed are believed to be fake, I will like help locating an equivalent available in the UK.Thanks in advance
 

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ericgibbs

Joined Jan 29, 2010
16,826
hi D,
Welcome to AAC.
I have been checking the datasheets of the 2SA1530 and the 2SC3940, I don't follow why you are asking for the different type ie: 2SA1530 .?
E
 

Thread Starter

DarkV

Joined Oct 14, 2022
9
Sorry, copying and pasting errors in the post but do not know how to edit, I will like to try and replace the transistors in the Fan circuit as a last-ditch attempt. I am having trouble locating these two Panasonic units 2SD2374PQAU & 2SC3940A. I want to try and fit equivalent units in the UK.
As I said I have replaced the fan, First was from Ali express which was noisier than the worn original unit. I then replaced it with a brushless unit following a guide from Youtube, but at high volume, it still cuts out (It did not cut out with the old work original, just very noisy and vibration). I have not replaced it with one that was from a working amp that had accidental water damage. But it still cuts out a high volume and the fan tries to spin but not very fast(Same symptom with brushless).
I do not have a scope so have no choice but the transistors change as the last throw of the dice.
 

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Dodgydave

Joined Jun 22, 2012
10,592
I would modify the fan cut out circuit, can you post the full diagram of the fan cutoff circuit?

The 2Sa transistor is just being used as a 16V regulator ..
 

Thread Starter

DarkV

Joined Oct 14, 2022
9
Sorry, copying and pasting errors in the post but do not know how to edit, I will like to try and replace the transistors in the Fan circuit as a last-ditch attempt. I am having trouble locating these two Panasonic units 2SD2374PQAU & 2SC3940A. I want to try and fit equivalent units in the UK.
As I said I have replaced the fan, First was from Ali express which was noisier than the worn original unit. I then replaced it with a brushless unit following a guide from Youtube, but at high volume, it still cuts out (It did not cut out with the old work original, just very noisy and vibration). I have not replaced it with one that was from a working amp that had accidental water damage. But it still cuts out a high volume and the fan tries to spin but not very fast(Same symptom with brushless).
I do not have a scope so have no choice but the transistors change as the last throw of the dice.
Screenshot 2022-10-14 162959.png
 

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Thread Starter

DarkV

Joined Oct 14, 2022
9
I would modify the fan cut-out circuit, can you post the full diagram of the fan cut-off circuit?

The 2Sa transistor is just being used as a 16V regulator ..
Hi D,
I cannot locate a UK source, I would consider using equivalent types, they have a typical specification.
Just in case you don't have them, the two datasheets are here,
E
That I will like help with finding equivalent units that will work as replacements as I am out of my comfort zone in regard to finding an alternative using the technical information on data sheets
 

Dodgydave

Joined Jun 22, 2012
10,592
The overload detection is picking up voltages from the speakers, it switches on transistors Q611 /612, as a test you can short out C601 or C611, this should disable the overload detection, but i would measure the voltages at the speakers at different volumes to see what happens..
 

Thread Starter

DarkV

Joined Oct 14, 2022
9
That I will like help with finding equivalent units that will work as replacements as I am out of my comfort zone in regard to finding an alternative using the technical information on data sheets
The overload detection is picking up voltages from the speakers, it switches on transistors Q611 /612, as a test you can short out C601 or C611, this should disable the overload detection, but i would measure the voltages at the speakers at different volumes to see what happens..
Thank you, will try shorting C601 tomorrow. My speakers are just a touch under 4 ohms ( 3.8 ohms) . Could that be the issue?
 

Thread Starter

DarkV

Joined Oct 14, 2022
9
I have not shorted it yet as I have now noticed that One channel has more bass than the other, my mate said he had the same issue (Lack of bass on one channel) caused by decoupling caps so I am going to replace the decoupling caps while I have the amp dismantled. I did measure the DC output and have attached the meter reading. I am keeping the amp volume below 11 o'clock and does not cut out. Many thank
 

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Thread Starter

DarkV

Joined Oct 14, 2022
9
I have not shorted it yet as I have now noticed that One channel has more bass than the other, my mate said he had the same issue (Lack of bass on one channel) caused by decoupling caps so I am going to replace the decoupling caps while I have the amp dismantled. I did measure the DC output and have attached the meter reading. I am keeping the amp volume below 11 o'clock and does not cut out. Many thank
Upon further examination, I found burn marks near the resistors.Losing hope now
 

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Thread Starter

DarkV

Joined Oct 14, 2022
9
That I will like help with finding equivalent units that will work as replacements as I am out of my comfort zone in regard to finding an alternative using the technical information on data sheets
I have replaced the bunt resistors and decoupling capacitors but the burn marks in the pictures above have me a bit worried. I have not been able to try it at hight volume as of yet.
 
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