BigEars86 Posted February 8, 2019 Share Posted February 8, 2019 Hello, I'm Karl. I have a Biema Q250 stereo power amplifier working in only one channel. When I power it up, the fan for the B-channel amplifier immediately comes on, the protect lights both light up, but the B-channel protect light remains lit. The two internal fuses on the power supply board are OK, and I can't see any obvious damage. The toroidal transformers are both putting out the correct voltage. Does anyone have any ideas about what could be wrong? Any help would be greatly appreciated! Link to comment Share on other sites More sharing options...
Addicted to music Posted February 8, 2019 Share Posted February 8, 2019 (edited) Most likely that the channel that’s not working is outputting an unacceptable level of DCV at the output. You’re lucky it has protection as DC can damage speakers by over heating there voice coil. Time to get it to an authorised service centre for repairs me think. BTW Karl, welcome to stereonet! Edited February 8, 2019 by Addicted to music Link to comment Share on other sites More sharing options...
BigEars86 Posted February 9, 2019 Author Share Posted February 9, 2019 Hello and thank you! Any ideas what could be causing the excessive DC? Shorted output transistors or a ceramic resistor gone on the fritz? I'm confident with replacing a part or two, but tracing faults is not my area of expertise. I'd like to have a go at it myself, but I think I might take it to a service centre. I'll upload a few photos Link to comment Share on other sites More sharing options...
BigEars86 Posted February 9, 2019 Author Share Posted February 9, 2019 Here are some photos (I hope I don't crash the site). Note the photo showing the front of the amp. It's been on for about 5 seconds, so the A channel has kicked on, but the B channel remains in protect mode. Note also that the B channel fan is spinning but the A channel fan is stationary. The only other thing I've noticed is a little bit of black dust on top of one of the white ceramic resistors (centre of second photo) on the main amp board. I've even wondered if one of the four thermistors is faulty, triggering the fan to come on and the amp to stay off! Link to comment Share on other sites More sharing options...
Zaphod Beeblebrox Posted February 9, 2019 Share Posted February 9, 2019 (edited) 2 hours ago, BigEars86 said: Hello and thank you! Any ideas what could be causing the excessive DC? Shorted output transistors or a ceramic resistor gone on the fritz? I'm confident with replacing a part or two, but tracing faults is not my area of expertise. I'd like to have a go at it myself, but I think I might take it to a service centre. I'll upload a few photos The ONLY way to service an amp like that is to: * Obtain a service manual, or schematic. * Using the usual suite of test equipment (multimeters, signal generator, oscilloscope, etc) trace the fault to the faulty component/s and replace them. It is impossible to advise you further, with much more data. Photos are not that useful. I believe Biema are distributed by Altronics. That should be your first phone call on Monday. Edited February 9, 2019 by Zaphod Beeblebrox Link to comment Share on other sites More sharing options...
BigEars86 Posted February 9, 2019 Author Share Posted February 9, 2019 Yes, its an Altronics unit. There is a 5-page schematic pdf on the altronics website. I'll print it out when I take it in for a service. Link to comment Share on other sites More sharing options...
Addicted to music Posted February 9, 2019 Share Posted February 9, 2019 18 hours ago, BigEars86 said: Hello and thank you! Any ideas what could be causing the excessive DC? Shorted output transistors or a ceramic resistor gone on the fritz? I'm confident with replacing a part or two, but tracing faults is not my area of expertise. I'd like to have a go at it myself, but I think I might take it to a service centre. I'll upload a few photos Im only guessing, note also it sounds like the protection in this unit is designed to switched the fans on during fault condition, that’s normal on most protection system when a fault is detected, and is usually the case for a variety of electronic products varying from office products to motor vehicles. Like @Zaphod Beeblebrox Said, it needs to be sitting on someone’s test bench to see what’s happening with the right tools. It could be anything you have listed and photos posted on line isn’t going to help much unless you see components “fritz” out. It’s great to see people willing to have a go, but with certain things like this if you’re unsure send it back to where it can get service. Usually with Altronics they employ people straight out of school and usually some one with experience in electronic repairs will fix that in the store, but you need to leave it there. 1 Link to comment Share on other sites More sharing options...
BigEars86 Posted February 10, 2019 Author Share Posted February 10, 2019 Thanks! Yes, the service centre sound like the best option. The last thing I want to do is muck something else up or waste time (and money) replacing parts that were fine anyway. I might have to take it in, but I'll be happier with that approach. I was hoping someone else had the exact same problem, and could advise me about a secret, hidden fuse that needs replacing. Oh well, it was worth a shot! When the faulty component(s) are found, I'll let everyone know what was up! By the way, I'd like to hear a few opinions about this amp and possibly its big bro the Q400 Link to comment Share on other sites More sharing options...
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