Repair Thule IA150B, no sound except humming - diyAudio
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Old 13th February 2017, 12:42 PM   #1
Moeses is offline Moeses  Sweden
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Default Repair Thule IA150B, no sound except humming

Hey,

I've got a broken Thule IA150B that I wanted to repair. I want some help on where to start, maybe it's a broken DC-bridge? ,

Anyway, the amplifier turns on just fine and the screen lights up, relay clicks and input selector works. However, the signal is not sent to the speakers. Instead I hear a rather loud humming noise around 200-300Hz which is not affected by volume control. All fuses seem to be ok, capacitors looks good on a first look. Only visual error is that the transformer is not attached . Any ideas?

Attached is two images and the service manual.

BR,
Moe
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Old 13th February 2017, 02:39 PM   #2
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I would check with an oscilloscope where the odd frequency is coming from first and then look for bad ground connections and good supply lines.
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Old 13th February 2017, 09:18 PM   #3
Moeses is offline Moeses  Sweden
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OK so I noticed a DC-voltage on S3 (left) but not on S4(right). This voltage was also present on P1 (left) but not on P101 (right). I then removed S3 and S4 and the DC-offset disappeared, but insted C122 went up in smoke. So I'm guessing there's something wrong with the REG9 or REG10, but I have no clue. Any help before I burn more components?

BR,
Moe
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Old 13th February 2017, 09:21 PM   #4
Ddave is offline Ddave  United States
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Perfectly dead capacitors can look perfectly good. An oscilloscope will tell quickly. Or measure the DC and ac on the main filter caps. The ac should be a lot lower than the dc.
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Old 13th February 2017, 09:26 PM   #5
Moeses is offline Moeses  Sweden
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I don't have access to an oscilloscope at the moment. Any way to determine which is bad and which is not with a multimeter?
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Old 14th February 2017, 06:20 PM   #6
Moeses is offline Moeses  Sweden
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So I have picked it apart more tonight. Now I can clearly see that some components are burnt. First picture shows C122 and the capacitors around it, second one the right channel and the third shows REG1 and REG2. Any idea how I can measure if the REG1/REG2 are ok?
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Old 15th February 2017, 08:49 AM   #7
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Quote:
Originally Posted by Moeses View Post
So I have picked it apart more tonight. Now I can clearly see that some components are burnt. First picture shows C122 and the capacitors around it, second one the right channel and the third shows REG1 and REG2. Any idea how I can measure if the REG1/REG2 are ok?
I think they have been running on high temperature for long period,not necessary burnt.

Anyway,unless you are able to isolate the load(circuit) from the regulator themselves,or else hard to determine are they confirm OK or not.

Yes,u can still try to measure the output voltages of the regulators with load connected,since I don't think that you want to cut the PCB traces.
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Old 15th February 2017, 10:00 AM   #8
Moeses is offline Moeses  Sweden
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Ok! The plan is to change all the 100uF 35V capacitors and see what happens. I have measured all the diodes and they seem fine.

Any other ideas?
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Old 15th February 2017, 02:38 PM   #9
Ddave is offline Ddave  United States
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You can use a multimeter on the main caps. Of course, there should be DC. Switch to AC and measure the ripple. Do this with no signal and no load, and with a load, still no signal.

Since yours is humming with no signal, these numbers should be enough to determine. I recently repaired an amp that didn't hum, but even with a very low signal level, the ripple on the failing main caps would cause a raspy distortion each cycle when the required output voltage tried to go above what was left in the caps between the peaks of the rectified AC coming in.,
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Old 16th February 2017, 06:53 PM   #10
Moeses is offline Moeses  Sweden
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Changed the the C21-C24, C121-C124 and C29-C32. Still same issue, still +19V DC offset oblekt channel on fuses, still loud humming in speakers. What could be faulty? AC/DC-converter? Measured the diodes bit they seem fine. Out of ideas, grateful for any help!

DDave: You mean the four large 10mF caps?

Last edited by Moeses; 16th February 2017 at 07:07 PM.
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