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Biema W220 ll Channel hum
Biema W220 ll Channel hum
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Old 10th April 2019, 04:29 PM   #21
nuryev is offline nuryev  Australia
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That will be the next step. I have the tools including braid and solder sucker. So will start on the weekend. Thanks
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Old 21st April 2019, 02:04 PM   #22
nuryev is offline nuryev  Australia
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UPDATE!!

Close inspection of solderside of pcb evidenced a broken GND track to the output plug on the main pcb - that was fixed with a short jumper!

I was fortunate enough to get a complete power supply from the company that manufactured the amplifiers more than 10 years ago! FREE OF CHARGE - beat that for after sales service! After installing the new psu, and the broken GND track fixed, the amp is now silent. On power, illuminates the blue power indicator, followed by an orange led which switches off after a soft click is heard - so the protection circuit is working!

The next stage troubleshooting why only one channel is playing! All the elimination processes were followed ie. Switch speakers, switch speaker cables, swith rca inputs on amp, switch rca's on pre-amp!

So far, voltages on the various channel resistors and diodes seem close enough.
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Old 21st April 2019, 02:11 PM   #23
TBTL is offline TBTL  Germany
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Great!

Try tracing the signal with an oscilloscope or a small AC-coupled amplifier with a protected input, like this: Project 164
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Old 21st April 2019, 02:59 PM   #24
nuryev is offline nuryev  Australia
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I have two dual channel scopes - a 20mhz and 50 mhz as well as a signal generator- might be an opportune time to dust them off! Only problem is I have limited experience with scopes on 240v equipment.
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Old 23rd April 2019, 05:09 PM   #25
nuryev is offline nuryev  Australia
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Quote:
Originally Posted by TBTL View Post
Great!

Try tracing the signal with an oscilloscope or a small AC-coupled amplifier with a protected input, like this: Project 164
I removed the ribbon cable from between the potentiometers on the control panel and the pcb. Withe the multi-connecter unplugged I traced the Left and right channel output to pins 9 and 13 respectively. When these pins are contacted individually with a dvm probe, scratchy sounds are produced out of both speakers!
Haven't pulled the scope out yet - busy weekend!
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Old 13th May 2019, 04:12 PM   #26
nuryev is offline nuryev  Australia
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UPDATE!
I has taken me some time to respond the kind people on diyaudio who assisted with my Biema 220 ii troubleshooting.

I needed some time to formulate a response that would not only embarrass me, but also serve to assist others who may find themselves in a similar situation - and hopefully save some time, money and effort.

While testing the the input lines from L and R rca inputs, I accidently short ciruited a regulator heat sink! The inevitable snap, crackle and pop..(not of the cereal variety) ensued, followed by the release of some 'magic smoke'!
Needless to say; that sinking feeling that it was the end of the amp......!

Fortunately, the protection relay kicked in and the amp switched off for a few seconds, then on again, and voila! Both channels were working! I kid you not!

PLEASE DO NOT TRY THIS AT HOME!
I DO NOT ACCEPT ANY RESPONSIBILITY for anyone using unscientific methods that cannot be replicated! This was purely by accident.

The conclusion being that the sudden spike probably cleared some oxidation from contacts in the relay switch. This was promptly replaced and after nearly 48 hours of almost continuous testing. The amp is now performing flawlessly.

If anyone has had similar experiences - or if there are any alternative hypotheses or explanations, I am interested in hearing of them.

Thank you to all for your interest and support.
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Old 13th May 2019, 04:14 PM   #27
nuryev is offline nuryev  Australia
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And now onto my Starving Student II headphone amp project!
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Old 15th May 2019, 04:03 PM   #28
kipman725 is offline kipman725  United Kingdom
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Quote:
Originally Posted by nuryev View Post
UPDATE!
I has taken me some time to respond the kind people on diyaudio who assisted with my Biema 220 ii troubleshooting.

I needed some time to formulate a response that would not only embarrass me, but also serve to assist others who may find themselves in a similar situation - and hopefully save some time, money and effort.

While testing the the input lines from L and R rca inputs, I accidently short ciruited a regulator heat sink! The inevitable snap, crackle and pop..(not of the cereal variety) ensued, followed by the release of some 'magic smoke'!
Needless to say; that sinking feeling that it was the end of the amp......!

Fortunately, the protection relay kicked in and the amp switched off for a few seconds, then on again, and voila! Both channels were working! I kid you not!

PLEASE DO NOT TRY THIS AT HOME!
I DO NOT ACCEPT ANY RESPONSIBILITY for anyone using unscientific methods that cannot be replicated! This was purely by accident.

The conclusion being that the sudden spike probably cleared some oxidation from contacts in the relay switch. This was promptly replaced and after nearly 48 hours of almost continuous testing. The amp is now performing flawlessly.

If anyone has had similar experiences - or if there are any alternative hypotheses or explanations, I am interested in hearing of them.

Thank you to all for your interest and support.
I fixed an amp (Cloud VTX750) where the only damage was that the tracks on both channels (on separate boards) that energised the relay contacts were subtly damaged. This meant the amp worked fine but the protection relays never disengaged. My initial thoughts were that the relays were damaged in some way but after replacing the tracks on both boards with wire the amp has worked perfectly. The weird thing is that the current in that track is limited to a maximum of 27mA by series resistors so the track can't have been damaged by over current. Furthermore all the nearby tracks are fine (so not some kind of chemical damage - although the damage to the track resembles chemical damage) and there are no tool marks from if the track was deliberately severed. The track is right at the edge of the PCB and in very strong airflow from the cooling fan, all I can think is that its some kind of wind abrasion of a track that as it was the edge of the board had a compromised solder mask/poor patterning.
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Old 16th May 2019, 12:35 AM   #29
nuryev is offline nuryev  Australia
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Hi Kipman,
Thanks for sharing your experience.

Co-incidentally, that was my initial finding when lifting the main pcb! A GRND track was lifted off the board, and yes the track was at the edge of the board, it also resembled chemical damage, but was limited to that track alone. Interesting that two amps from different manufacturers can present with such similar failures.

I suspected mechanical damage, but The copper itself appeared to be disintegrating along approximately 8-10cm. I removed the track and replaced it with a jumper! The channel still did not work though although a hum disappeared.
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Old 16th May 2019, 05:11 PM   #30
kipman725 is offline kipman725  United Kingdom
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Quote:
Originally Posted by nuryev View Post
Hi Kipman,
Thanks for sharing your experience.

Co-incidentally, that was my initial finding when lifting the main pcb! A GRND track was lifted off the board, and yes the track was at the edge of the board, it also resembled chemical damage, but was limited to that track alone. Interesting that two amps from different manufacturers can present with such similar failures.

I suspected mechanical damage, but The copper itself appeared to be disintegrating along approximately 8-10cm. I removed the track and replaced it with a jumper! The channel still did not work though although a hum disappeared.
Yep exactly the same situation on two boards vertically stacked above each other.
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