timmyi23 Posted April 29, 2013 Share Posted April 29, 2013 Hi. Half way through gig and the sound cut out from my Hartke 3500 head. Have tested with alternative leads and cables. The unti powers up ok with all lights coming on, fan working and when bass is plugged in the compression light blinks as normal. I just disconnected the power amp module from the pre-amp and it blew the pwer fuse! Any ideas what the problem is?? Cheers Tim Quote Link to comment Share on other sites More sharing options...
MarkBassChat Posted April 30, 2013 Share Posted April 30, 2013 Failed power supply, or the power amp. The most frequentlt the problem is caused by shorted output transistors. Mark Quote Link to comment Share on other sites More sharing options...
timmyi23 Posted April 30, 2013 Author Share Posted April 30, 2013 Mark Thanks for your response mate. I'm a bit of a novice when it comes to internal electrics and circuitry but can't afford to get it repaired so happy to take a look myself and am a pretty quick learner. I noticed that each time I switched the unit on it was constantly blowing the power circuit fuse, however with the power amp module disconnected it all starts ok and the pre-amp shows all lights, and fan working? Any idea on this? If you could help me identify and locate specific components that would be great. Thanks Tim Quote Link to comment Share on other sites More sharing options...
MarkBassChat Posted April 30, 2013 Share Posted April 30, 2013 (edited) Be warned that the amp contains dangerous voltages and there is no room for mistakes when you deal with such voltages. Previously you said that the amp blew the power fuse when you disconnected the power amp module from the pre-amp. In the last post you said exactly the oposite: when you disconnected the power amp, the rest of the amp is working. Which way is it? I think that the second post is more accurate. First you have to identify modules in the amp: the preamp, the power amp, the power supply and the transformer (part of the power supply). I susspect that what you are doing is disconnecting the power amp from the power supply (correct me if I'm wrong). In this case the preamp works (you can check that the valve is glowing and you have signal both of the Effect Send output as well as on the DI output). The Power LED os on and the fan is working. This proves that the preamp and the power supply (including the transformer) is OK. This means that the power amp is shorted (output transistors). And in this case I'm sorry but it is too difficult for a novice to desolder the transistors. Appart from the output transistors quite often driver transistors fail (along with the quiescent current regulator). So my advise is to confirm that you disconnect the power amp from the power supply (and not from the preamp), verify that the preamp is working, check the output transistors for shorts (with a digital multimeter) and that's it. If the transistors are shorted, the only thing you can do is to take it to a tech. If you are not sure what you are disconnecing, make a photo and post it here. Also make sure that the fuse that you had previously is of the correct type: it should be 4A - slow blow. Sometimes people use fast fuses and this is the whole source of the problem. Mark Edited April 30, 2013 by MarkBassChat Quote Link to comment Share on other sites More sharing options...
timmyi23 Posted April 30, 2013 Author Share Posted April 30, 2013 Mark, thanks again mate. Yes sorry, to be clear in the first post I had just disconnected the power amp from the pre amp board. The second post is the accurate one as the fuse does not blow when the power lead is disconnected from the power amp. Thanks Tim Quote Link to comment Share on other sites More sharing options...
lonestar Posted April 30, 2013 Share Posted April 30, 2013 I had a ha5000 that failed due to burnt out output transistor. Was fixed under warranty by importer thanks to CODA music in Stevenage a few years ago. Quote Link to comment Share on other sites More sharing options...
RandomBass Posted May 3, 2013 Share Posted May 3, 2013 Yes that sounds suspiciously like defective output devices. Do you have anything you can plug the effect send into to see if you are getting a sensible signal and sound from the pre amp section? Another amp or something will do. Cheers Geoff Quote Link to comment Share on other sites More sharing options...
RandomBass Posted May 3, 2013 Share Posted May 3, 2013 Yes that sounds suspiciously like defective output devices. Do you have anything you can plug the effect send into to see if you are getting a sensible signal and sound from the pre amp section? Another amp or something will do. Cheers Geoff Quote Link to comment Share on other sites More sharing options...
shizznit Posted May 3, 2013 Share Posted May 3, 2013 [quote name='lonestar' timestamp='1367348963' post='2064579'] I had a ha5000 that failed due to burnt out output transistor. Was fixed under warranty by importer thanks to CODA music in Stevenage a few years ago. [/quote] That happened twice with my old HA500. An easy and inexpensive fix for an experience tech. Quote Link to comment Share on other sites More sharing options...
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