geoffbyrne Posted September 26, 2011 Share Posted September 26, 2011 [IMG]http://img.photobucket.com/albums/v213/geoffbyrne/P1010042.jpg[/IMG] [IMG]http://img.photobucket.com/albums/v213/geoffbyrne/P1010041.jpg[/IMG] Long story short - bought cheap (£22) keyboard amp (Calrsboro) off t'Ebay for practices & driving foldback cab. Turned it on the other day (it's been fine for a couplke of months) & it blew bigtime - no magic smoke, but low frequency fluctuation. All fuses blown. Replaced all fuses & now blows only internal fuses - see pics. Anyone point to why? And is it worth repairing? G. Quote Link to comment Share on other sites More sharing options...
Mr. Foxen Posted September 26, 2011 Share Posted September 26, 2011 Could be loads of things, only way it is worth trying to find what on an amp that cheap is so you know a bit more about such things for next time. Quote Link to comment Share on other sites More sharing options...
Subthumper Posted September 26, 2011 Share Posted September 26, 2011 I would suspect its either the bridge rectifier, or the power transistors. You will need to take it to a techie to find out for sure. If it was blowing the mains fuse then I'd suspect the transformer. Either way its gonna be more than you paid for it unless you have a techie friend who will fix it for beers plus the cost of components. Good luck Cheers Just Quote Link to comment Share on other sites More sharing options...
geoffbyrne Posted September 26, 2011 Author Share Posted September 26, 2011 [quote name='Subthumper' timestamp='1317050008' post='1385970'] I would suspect its either the bridge rectifier, or the power transistors. You will need to take it to a techie to find out for sure. If it was blowing the mains fuse then I'd suspect the transformer. Either way its gonna be more than you paid for it unless you have a techie friend who will fix it for beers plus the cost of components. Good luck Cheers Just [/quote] Yeah, that's what I reckoned. It's a bin case. Problem is, I really need an amp to run the foldback & this was light & cheap. So I'm still looking for something light & cheap................. Thanks for the input guys. G. Quote Link to comment Share on other sites More sharing options...
TimR Posted September 26, 2011 Share Posted September 26, 2011 What's going on with the bodged bit of chockie block going off to that Jack? Quote Link to comment Share on other sites More sharing options...
KingBollock Posted September 26, 2011 Share Posted September 26, 2011 I had a Carlsboro Bass amp that was blowing fuses and it was the Bridge Rectifier. Obviously it's not necessarily the same problem for you, but if it is it's easily tested for and cheaply fixed. Quote Link to comment Share on other sites More sharing options...
Slipperydick Posted September 26, 2011 Share Posted September 26, 2011 Couple of points. 1, do the fuses blow instantly, or after a second or so. and 2, are they blackened when they do blow, or do they just blow softly ?? Quote Link to comment Share on other sites More sharing options...
geoffbyrne Posted September 27, 2011 Author Share Posted September 27, 2011 No idea about the chockie-block thingie - it's as it was when I got it - as I said, it all worked fine for a while. @Slipperydick: they're blackened when they blow & it's not quite instantaneous. G. Quote Link to comment Share on other sites More sharing options...
Mr. Foxen Posted September 27, 2011 Share Posted September 27, 2011 If it is a bin job, whip out that reverb tank, they are handy, and the transformer has a scrap value if you accumulate such things (or know someone that does). Quote Link to comment Share on other sites More sharing options...
geoffbyrne Posted September 27, 2011 Author Share Posted September 27, 2011 [quote name='Mr. Foxen' timestamp='1317121861' post='1386913'] If it is a bin job, whip out that reverb tank, they are handy, and the transformer has a scrap value if you accumulate such things (or know someone that does). [/quote] Yes...... That had occured to me. Could always stick it on Ebay for 'Spare or Repair'........ G. Quote Link to comment Share on other sites More sharing options...
Mr. Foxen Posted September 27, 2011 Share Posted September 27, 2011 Seperate reverb tanks seems to sell better. People find them that way, guess put reverb tank in the listing title. Quote Link to comment Share on other sites More sharing options...
Slipperydick Posted September 27, 2011 Share Posted September 27, 2011 [quote name='geoffbyrne' timestamp='1317114770' post='1386782'] No idea about the chockie-block thingie - it's as it was when I got it - as I said, it all worked fine for a while. @Slipperydick: they're blackened when they blow & it's not quite instantaneous. G. [/quote] Both fuses instanly blackened ( not the mains fuse) probably means a dead short, so the bridge rec is favourite I reckon. its the black square thing on the heatsink in your photos. If you have a multimeter take the fuses out and measure it on the low ohms range across the two diagonally opposite terminals marked with a sort of an S. If its a short, its duff. couple of quids from somewhere like Maplins should sort you out. Depends on whether you feel up to changing it yourself. Leave the PCB fuses out, and and try powering it up, if the mains fuse fails your transformer is probably knackered. Dont try any of the above if you dont feel confident enough with electrickery stuff though. Quote Link to comment Share on other sites More sharing options...
geoffbyrne Posted September 28, 2011 Author Share Posted September 28, 2011 [quote name='Slipperydick' timestamp='1317137670' post='1387229'] Both fuses instanly blackened ( not the mains fuse) probably means a dead short, so the bridge rec is favourite I reckon. its the black square thing on the heatsink in your photos. If you have a multimeter take the fuses out and measure it on the low ohms range across the two diagonally opposite terminals marked with a sort of an S. If its a short, its duff. couple of quids from somewhere like Maplins should sort you out. Depends on whether you feel up to changing it yourself. Leave the PCB fuses out, and and try powering it up, if the mains fuse fails your transformer is probably knackered. Dont try any of the above if you dont feel confident enough with electrickery stuff though. [/quote] Mmmmm. Interesting. I'll get round to trying this in the next few days - I've clobbered it all back together & screwed up the screws at the moment. The Good Lady has just had a hip replacement & currently needs a lot of 'lift & lay' support, so I'm a bit distracted....... G. Quote Link to comment Share on other sites More sharing options...
deanbean502 Posted October 12, 2011 Share Posted October 12, 2011 short on transformer windings Quote Link to comment Share on other sites More sharing options...
MarkBassChat Posted October 13, 2011 Share Posted October 13, 2011 [quote name='deanbean502' timestamp='1318455141' post='1402550'] short on transformer windings [/quote]No, only the internal fuses blow. It means that this is either the bridge rectifier or output transistors. Most often this is caused by shorted output transistors (as already mentioned by Subthumper). Can be easily fixed but you need to have some tools, meter and parts to be replaced. Mark Quote Link to comment Share on other sites More sharing options...
geoffbyrne Posted October 13, 2011 Author Share Posted October 13, 2011 (edited) For the aforesaid reason I haven't done anything about this, but when I get around to it, it looks like the bridge rectifier is neither too expensive not very difficult to replace, so I'll see if I can (1) remove rectifier, ( 2) get a replacement at Maplin's and (3) replace in situ. If that don't work, I'll be asking Mark about the transistors. G. Edited October 13, 2011 by geoffbyrne Quote Link to comment Share on other sites More sharing options...
MarkBassChat Posted October 13, 2011 Share Posted October 13, 2011 G. In 90% of cases it's rather the transistors that are shorted and only in 10% (or less) you can blame the bridge rectifier. It can be asily checked with a cheap multimeter and I advise you not to replace it without checking it first. I was trying to suggest to take the amp to someone who knows how to check the transistors and the brigde. The problem is that if the transistors are shorted, most probably few more components have failed (e.g. driver transistors or resistors). And even if you replace the output transistors (only), the amp may still not be working. This would be a waste of time and money. It looks like not very complicated problem but still some technical knowledge is required. Can you make a photo of the output transistors (on the heatsink), maybe some problems will be visible? Mark Quote Link to comment Share on other sites More sharing options...
geoffbyrne Posted October 13, 2011 Author Share Posted October 13, 2011 This amp cost me £22, Mark - is it worth it? G. Quote Link to comment Share on other sites More sharing options...
Slipperydick Posted October 13, 2011 Share Posted October 13, 2011 Easy way to check if the O/P Transistors are shorted. Remove the screws, and measure between the case and the 2 soldered pins on the bottom of them using a digital multimeter on a low ohms range -not diode test- if you can read anything at all, theyre duff. Again cheap - usually, especially if theyre just 2N3055s but stands a good chance the drivers are also duff. Quote Link to comment Share on other sites More sharing options...
MarkBassChat Posted October 13, 2011 Share Posted October 13, 2011 [quote name='geoffbyrne' timestamp='1318521894' post='1403298'] This amp cost me £22, Mark - is it worth it? G.[/quote]Yes, it is. The reverb spring alone is worth £22. So you have the rest of the amp for free. The only problem is that most probably you cannot fix it on your own. So you have to find out how to do it cheap. Check the output transistors as advised and then decide what to do later. Doesn't any of your friends know anything about electronics? I could guide him what to do. You could also start from providing the symbol of the amp and also looking for the schematic of the amp. You can also ask for advise (and the schematic) on this forum: [url="http://music-electronics-forum.com/f22/"]http://music-electronics-forum.com/f22/[/url] Mark Quote Link to comment Share on other sites More sharing options...
Slipperydick Posted October 13, 2011 Share Posted October 13, 2011 [quote name='MarkBassChat' timestamp='1318523380' post='1403321'] Yes, it is. The reverb spring alone is worth £22. So you have the rest of the amp for free. The only problem is that most probably you cannot fix it on your own. So you have to find out how to do it cheap. Check the output transistors as advised and then decide what to do later. Doesn't any of your friends know anything about electronics? I could guide him what to do. You could also start from providing the symbol of the amp and also looking for the schematic of the amp. You can also ask for advise (and the schematic) on this forum: [url="http://music-electronics-forum.com/f22/"]http://music-electro...-forum.com/f22/[/url] Mark [/quote] Could you replace it for £22. Whats it worh when its repaired compared to what its worth now & would you enjoy doing it ? btw, which model is it, if its an old one, I might have a schematic if its any use to you. Prhaps its just me, but I hate to see anything scrapped when its still got some usful life in it. Quote Link to comment Share on other sites More sharing options...
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