Home |
Search |
Today's Posts |
|
Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems. |
Reply |
|
LinkBack | Thread Tools | Display Modes |
#1
Posted to sci.electronics.repair
|
|||
|
|||
Mark Bass ,CMD 102P, bass amp of 2011
Owner switched on, blue led came on as normal , but between that and 20
seconds grabbing guitar lead, had blown the mains fuse, no input, usual load. No problem in previous use, may be a drop in volume , as for the last month had to use 6 instead of 4 on the volume, but uses different cabs so cannot be certain of that. Both IRFP27N60K ohmic low all round. With trade mark ground off 8pin SMPS supervisor, from combined effort here a few years ago, probably IR2153 ,if like the other flavors of these amps. Any view as to what would cause this sort of failure? and pre-emptive mod around the supervisor circuit? I don't like the great thick slabs of ceramic insulator pads, should be used on bathroom splash-backs IMHO , not heat conductors. The main amps not checked over yet. |
#2
Posted to sci.electronics.repair
|
|||
|
|||
Mark Bass ,CMD 102P, bass amp of 2011
1 of 3 of each n and p type paralleled audio powerFETs gone ohmic all
round, IRFP240 and IRFP9240. So a month ago 1 failed then the other soon after, both failing safe and non-functional? then both going shorted at the last power-up? |
#3
Posted to sci.electronics.repair
|
|||
|
|||
Mark Bass ,CMD 102P, bass amp of 2011
"N_Cook" wrote in message ... Owner switched on, blue led came on as normal , but between that and 20 seconds grabbing guitar lead, had blown the mains fuse, no input, usual load. No problem in previous use, may be a drop in volume , as for the last month had to use 6 instead of 4 on the volume, but uses different cabs so cannot be certain of that. Both IRFP27N60K ohmic low all round. With trade mark ground off 8pin SMPS supervisor, from combined effort here a few years ago, probably IR2153 ,if like the other flavors of these amps. Any view as to what would cause this sort of failure? and pre-emptive mod around the supervisor circuit? I don't like the great thick slabs of ceramic insulator pads, should be used on bathroom splash-backs IMHO , not heat conductors. The main amps not checked over yet. Good luck with that. This is one manufacturer I refuse point blank to repair. Gareth. |
#4
Posted to sci.electronics.repair
|
|||
|
|||
Mark Bass ,CMD 102P, bass amp of 2011
On 12/05/2016 20:34, Gareth Magennis wrote:
"N_Cook" wrote in message ... Owner switched on, blue led came on as normal , but between that and 20 seconds grabbing guitar lead, had blown the mains fuse, no input, usual load. No problem in previous use, may be a drop in volume , as for the last month had to use 6 instead of 4 on the volume, but uses different cabs so cannot be certain of that. Both IRFP27N60K ohmic low all round. With trade mark ground off 8pin SMPS supervisor, from combined effort here a few years ago, probably IR2153 ,if like the other flavors of these amps. Any view as to what would cause this sort of failure? and pre-emptive mod around the supervisor circuit? I don't like the great thick slabs of ceramic insulator pads, should be used on bathroom splash-backs IMHO , not heat conductors. The main amps not checked over yet. Good luck with that. This is one manufacturer I refuse point blank to repair. Gareth. At least a close enough schematic is on elektrotanya. I started looking at any common factor between the failed powerFETs. They are not symetrically disposed, but a 100V 33uF main +rail decoupler is physically near one failed FET and the other rail cap near the other FET. I'll check the ESR but will replace them anyway. Some sort of very large dV/dt or high level hf/rf that knocked out the adjacent FETs but got attenuated along the common lines to the other pairs of FETS perhaps.? Add some ferrite beads as well? Needs something adding , instead of just replacing the expensive powerFETs especially if the caps ESRs are good |
#5
Posted to sci.electronics.repair
|
|||
|
|||
Mark Bass ,CMD 102P, bass amp of 2011
"N_Cook" wrote in message ... On 12/05/2016 20:34, Gareth Magennis wrote: "N_Cook" wrote in message ... Owner switched on, blue led came on as normal , but between that and 20 seconds grabbing guitar lead, had blown the mains fuse, no input, usual load. No problem in previous use, may be a drop in volume , as for the last month had to use 6 instead of 4 on the volume, but uses different cabs so cannot be certain of that. Both IRFP27N60K ohmic low all round. With trade mark ground off 8pin SMPS supervisor, from combined effort here a few years ago, probably IR2153 ,if like the other flavors of these amps. Any view as to what would cause this sort of failure? and pre-emptive mod around the supervisor circuit? I don't like the great thick slabs of ceramic insulator pads, should be used on bathroom splash-backs IMHO , not heat conductors. The main amps not checked over yet. Good luck with that. This is one manufacturer I refuse point blank to repair. Gareth. At least a close enough schematic is on elektrotanya. I started looking at any common factor between the failed powerFETs. They are not symetrically disposed, but a 100V 33uF main +rail decoupler is physically near one failed FET and the other rail cap near the other FET. I'll check the ESR but will replace them anyway. Some sort of very large dV/dt or high level hf/rf that knocked out the adjacent FETs but got attenuated along the common lines to the other pairs of FETS perhaps.? Add some ferrite beads as well? Needs something adding , instead of just replacing the expensive powerFETs especially if the caps ESRs are good Yeah, yeah yeah. That's why I won't repair this stuff. Gareth. |
#6
Posted to sci.electronics.repair
|
|||
|
|||
Mark Bass ,CMD 102P, bass amp of 2011
good ESR and uF value of those 2 caps and the main ps rail caps.
Thin ground traces going to those 33uF caps, so looks like some of those otherwise mysterious retrofit pieces of overlain wires will be going in there. |
#7
Posted to sci.electronics.repair
|
|||
|
|||
Mark Bass ,CMD 102P, bass amp of 2011
At least there is vertical clearance on the pins of the replacement
audio TOP-3, to slide on some ferrite beads. |
#8
Posted to sci.electronics.repair
|
|||
|
|||
Mark Bass ,CMD 102P, bass amp of 2011
"N_Cook" wrote in message ... At least there is vertical clearance on the pins of the replacement audio TOP-3, to slide on some ferrite beads. https://www.youtube.com/watch?v=1IT5ogF4C-8 Gareth. |
Reply |
Thread Tools | Search this Thread |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Forum | |||
Eden Bass Amp | Electronics Repair | |||
Mark Bass Combo Head, CMD 121H, of 2005 | Electronics Repair | |||
250W amp - Mark Bass , Little Mark 250, of 2008, Italy | Electronics Repair | |||
Ashdown Bass amp | Electronics Repair | |||
Ashdown Mag 200 bass amp | Electronics Repair |