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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. |
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#1
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Marshall JVM 410, 2006, PbF
Early and bad PbF but is it the problem here, most of the ECC83 socket
solderings were very iffy . Volume dropped and owner changed the valves. Volume came up but a distortion on the overdrive channels emerged soon after. Redoing those socket solderings and usual suspects on front controls board has not cured the distortion problem. schematic on elektrotanya Harsh cut-off more like clipping and no sign of any smooth saturation, rounding of the peak/s, just launches into cut off on the peaks (not troughs). With all pots at mid posistion the signals ,clean and OD, are sinusoidal and amplitude ratio of about 2:1 OD:Clean in the gain and tone block. That preceeds the valve V7 which with mid pots and order 10mV amp input 400 Hz has on pin2 , grid, about 100mV pk-pk for clean but 7 volt on OD thence clipping. All valves test fine, all R in relevant area are fine. A cap problem ? but coinciding with valve changing? I've not inspected underside of that wired-in board but I'm assuming a cap PbF solder problem. Vol drop could even be the bad PbF at the input socket but problems appearing / disappearing at "intimate" handling suggest PbF problems. There is loads of relays in this design also . |
#2
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Marshall JVM 410, 2006, PbF
"N_Cook" wrote in message ... Early and bad PbF but is it the problem here, most of the ECC83 socket solderings were very iffy . Volume dropped and owner changed the valves. Volume came up but a distortion on the overdrive channels emerged soon after. Redoing those socket solderings and usual suspects on front controls board has not cured the distortion problem. schematic on elektrotanya Harsh cut-off more like clipping and no sign of any smooth saturation, rounding of the peak/s, just launches into cut off on the peaks (not troughs). With all pots at mid posistion the signals ,clean and OD, are sinusoidal and amplitude ratio of about 2:1 OD:Clean in the gain and tone block. That preceeds the valve V7 which with mid pots and order 10mV amp input 400 Hz has on pin2 , grid, about 100mV pk-pk for clean but 7 volt on OD thence clipping. All valves test fine, all R in relevant area are fine. A cap problem ? but coinciding with valve changing? I've not inspected underside of that wired-in board but I'm assuming a cap PbF solder problem. Vol drop could even be the bad PbF at the input socket but problems appearing / disappearing at "intimate" handling suggest PbF problems. There is loads of relays in this design also . Try cleaning/resolderig all the send and return jack sockets, and their accociated switches, particularly the Power Amp In socket. Gareth. Gareth. |
#3
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Marshall JVM 410, 2006, PbF
"Gareth Magennis" wrote in message ... "N_Cook" wrote in message ... Early and bad PbF but is it the problem here, most of the ECC83 socket solderings were very iffy . Volume dropped and owner changed the valves. Volume came up but a distortion on the overdrive channels emerged soon after. Redoing those socket solderings and usual suspects on front controls board has not cured the distortion problem. schematic on elektrotanya Harsh cut-off more like clipping and no sign of any smooth saturation, rounding of the peak/s, just launches into cut off on the peaks (not troughs). With all pots at mid posistion the signals ,clean and OD, are sinusoidal and amplitude ratio of about 2:1 OD:Clean in the gain and tone block. That preceeds the valve V7 which with mid pots and order 10mV amp input 400 Hz has on pin2 , grid, about 100mV pk-pk for clean but 7 volt on OD thence clipping. All valves test fine, all R in relevant area are fine. A cap problem ? but coinciding with valve changing? I've not inspected underside of that wired-in board but I'm assuming a cap PbF solder problem. Vol drop could even be the bad PbF at the input socket but problems appearing / disappearing at "intimate" handling suggest PbF problems. There is loads of relays in this design also . Try cleaning/resolderig all the send and return jack sockets, and their accociated switches, particularly the Power Amp In socket. Gareth. Gareth. And check that a send/return loop isn't engaged with the Mix pot on anything other than fully on or off - not sure which way drops the volume with no effects plugged in. Gareth. |
#4
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Marshall JVM 410, 2006, PbF
Gareth Magennis wrote in message
... "Gareth Magennis" wrote in message ... "N_Cook" wrote in message ... Early and bad PbF but is it the problem here, most of the ECC83 socket solderings were very iffy . Volume dropped and owner changed the valves. Volume came up but a distortion on the overdrive channels emerged soon after. Redoing those socket solderings and usual suspects on front controls board has not cured the distortion problem. schematic on elektrotanya Harsh cut-off more like clipping and no sign of any smooth saturation, rounding of the peak/s, just launches into cut off on the peaks (not troughs). With all pots at mid posistion the signals ,clean and OD, are sinusoidal and amplitude ratio of about 2:1 OD:Clean in the gain and tone block. That preceeds the valve V7 which with mid pots and order 10mV amp input 400 Hz has on pin2 , grid, about 100mV pk-pk for clean but 7 volt on OD thence clipping. All valves test fine, all R in relevant area are fine. A cap problem ? but coinciding with valve changing? I've not inspected underside of that wired-in board but I'm assuming a cap PbF solder problem. Vol drop could even be the bad PbF at the input socket but problems appearing / disappearing at "intimate" handling suggest PbF problems. There is loads of relays in this design also . Try cleaning/resolderig all the send and return jack sockets, and their accociated switches, particularly the Power Amp In socket. Gareth. Gareth. And check that a send/return loop isn't engaged with the Mix pot on anything other than fully on or off - not sure which way drops the volume with no effects plugged in. Gareth. Will do. I removed the main board and no obvious PbF problems found but treated all the usual suspects. I did note that the 1 1/4 inch fuse holders would have failed solder in a short while. |
#5
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Marshall JVM 410, 2006, PbF
not S/R loop problem
Just in case it was an odd batch of ECC83 , I tried with others and the same. Keeping same input and changing frequency 4KHz , 26V pk-pk on V7a grid , pin 7, and ok normal soft roll top "clipping" 2KHz, 48V pk-pk , bad trace hard clipping 1 K , 35V , bad 200, 15V bad 100 Hz, 5V, normal trace shape so to find an errant cap that is involved in OD1 and OD2 channels |
#6
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Marshall JVM 410, 2006, PbF
Tomorrow I think the 1uF on the cathode of the first triode needs exploring
as its output is upped in the 400 - 1000 Hz area. Of course a bit exagerated, in that frequency domain in the clean channel, could well go unnoticed. |
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