Crest 8001 4 ohm bridge |
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levyte357-
Old Croc Joined: 27 July 2012 Location: UK, South East Status: Offline Points: 8128 |
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Got my mind made up mate. Will try one of the most serious lightweights ever made, then if that doesn't give me what I want, will try transformer. |
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Global Depopulation - Alive and Killing.
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tilla
New Member Joined: 07 July 2020 Location: London Status: Offline Points: 6 |
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Hi guys,
I was hoping you could help me out here. I have two of these amps. One had a burnt output relay on one side which was an easy fix the other one i had to rebuild one output stage completely. It had a burnt pcb at place and many output transistors and resistors failed. Long story I put it all back now and both channels works fine. I am wondering however what the next steps will be. I d need to test the amps somehow, how do i do this without the load resistors. Will I need to bias all channels, the one a rebuilt perhaps is a no brainier but how about the others ? How do I know if capacitors failing, without removing them one by one and testing them? I would like the amps to be safe to operate the least of course if i could restore them to factory spec that would be amazing for now however safety is my first concern. One thing I noticed the amp that i fixed on one channel seem to not to have a working soft start. What I mean is as soon I press the power on button at the front all the relays pull in including the output relays and the supply relays. It also causes a pop on the connected speaker. How do I start investigating this? I consider myself lucky to be able to have the none working side fixed so far as I have no previous experience in fixing amplifiers. I do have a large bag enthusiasm thought and i am good at taking my time when it comes to complex issues like this. It took me about 3 months to get to this stage. I have the time and the patience I only need your advice which of course will be highly appreciated .
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tilla
New Member Joined: 07 July 2020 Location: London Status: Offline Points: 6 |
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Following up from my questions. I started looking around on eBay for dummy loads. I m not sure if what I am looking at is actually suitable for this purpose. Would these work:
https://www.ebay.co.uk/itm/Resistance-Dummy-Load-Audio-1000W-4-8-16-ohm-aluminium-shell-braking-resistor-UK/223769625570?var=522499714303 I am thinking of buying two 8ohm ones. With that I could test both side @ 8hms at the same time or one side @4ohms with them in parallel Will the above resistors work I wonder?
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Earplug
Old Croc Joined: 03 January 2012 Location: Europe Status: Offline Points: 7199 |
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Yes - those look ok. |
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Earplugs Are For Wimps!
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tilla
New Member Joined: 07 July 2020 Location: London Status: Offline Points: 6 |
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Perfect! Thanks Earplug ! Got a pair of those. Looking forward to start testing.
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Earplug
Old Croc Joined: 03 January 2012 Location: Europe Status: Offline Points: 7199 |
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No problem. And maybe screw them down onto some Alu - and/or stick a fan on them. They can get hot. |
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Earplugs Are For Wimps!
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tilla
New Member Joined: 07 July 2020 Location: London Status: Offline Points: 6 |
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Good Idea, I have a couple of spare fans at home I will stick them on top. How would I go about testing the amp with these. Is there a suggested time limit I can ran the amp with these or as long as the amp able to ? ( I suppose this is the aim of the test isnt it ) What is too hot for these ? How will i notice when something starts going wrong if anything ?
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Earplug
Old Croc Joined: 03 January 2012 Location: Europe Status: Offline Points: 7199 |
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When testing, I usually let the amp under test run for 20-30 minutes. That should show up any problems. And you know something's going wrong when the magic smoke appears!! OR:- Get a couple of these to keep track of the temperatures - |
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Earplugs Are For Wimps!
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tilla
New Member Joined: 07 July 2020 Location: London Status: Offline Points: 6 |
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Thanks again Earplug much appreciated. I have an infrared thermometer which i was planning to use and will also get a couple of the ones you suggest. That looks a very handy tool for such cheap money. in anyways I suppose I want to see if all output transistors warm up and have the same temperature between them, correct ? Ive seen videos guys touching transistors and testing by hand. How hot are they meant to be ? Or its the only important thing is they all are roughly on the same temperature ? Edited by tilla - 24 November 2020 at 6:08pm |
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Earplug
Old Croc Joined: 03 January 2012 Location: Europe Status: Offline Points: 7199 |
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The output transistors should all be around the same temperature. It would be odd if one was a lot hotter. Testing (carefully) by hand is ok - but I think that 40º or 50º will burn, so using a probe is far better. |
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Earplugs Are For Wimps!
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