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Finally having cleaned out the broken gear shelves (at CenterStaging, Burbank, CA), I've been able to start in on Preventative Maintenance on our Rental Inventory, beginning with the Marshall JCM2000's. There were several that had never been into the shop (since I've been here) for over 5 years. Those who know the amp well, know that rear panel PCB & Bias Board is definitely optimum for causing amp failures if not caught in time.
Caught what? SOLDER FRACTURES. The Rear panel PCB assembly on the JCM2000 models, be it the TSL, the DSL50 & DSL100's all use the same board layout. What I find on EVERY one of these amps from constant road use is radial solder fractures around the Impedance Select Switch for staters. That's OPEN circuit on the OT....no output, while you're driving the amp open circuit. Also, the SPEAKER OUTPUT JACKS. 80% of what I've just gone thru....radial solder fractures on those as well.
There is a certain satisfying attribute to solder fractures, where it sometimes works and sometimes not....you can give the amp a big SLAP on the top, to wake it back up!! Until it stops again.
On the TSL, I've never seen one come in WITHOUT fractures on most of the 8-pin DIN Footswitch connector. Last one, every contact was fractured. Eh...didn't need the foot switch anyhow. XLR Direct Out....ALWAYS fractues on those contacts.
The +/- 15V supply dropping resistors.....fractures on those most of the time. AND, the Effects Loop jacks.
I.E, ANY of the REAR PANEL JACKS & HARDWARE that are used to support the PCB assembly......Marshall's engineering staff seems to believe (as so many other MFGR's do) you can support PCB's by their solder connections of panel mounted parts. Don't need no stinkin' mechanical support brackets that raise the cost half a buck! HAH!
The AC Mains board assy.....50% of those had radial fractues around the IEC 320 AC Mains connector, and many also had fractures on the AC & HT fuse posts.
Getting at the Bias board on these amps.....ya gotta pull the main PCB up to extract it. But, before getting to that, I had 25% of the power tube sockets with solder fractures. Sometimes had them on the filter caps, periodically on the elevated Screen & supply 5W resistors. All the rest of the parts on those boards...rarely find faults, as far as solder fractures go.
The bias board....all too often, radial fractures around one or more of the pot leads. (While I'm on those boards, I'll seep in some Caig DeOxit into the pot, and exercise it, then re-set it where it was for a starting point when it's powered back up). And same on the 7-pin connector, as well as on the 3-terminal header used for DMM connections externally.
De-solder, THEN Re-solder. NOT just add solder.
On the front panel boards, for starters, all the pot hardware is finger tight, if not already coming off. Most always solder fractures on the INPUT jack. The front panel pots....they do use a 2-point support bracket....BUT....Marshall's layout staff only used the thinnest Annular Ring around those tabs. Try and de-solder & re-solder to solidify those support tabs......you just broke the adhesion of the annular ring to the PCB!! Hate it when non-service folk do board layouts! You're etching all that copper (full sheet of it) and flushing it down the drain, when you COULD lay in substantial land area to anchor components to.
The small Reverb board over in the front left corner is usually ok.
The Reverb Tanks....biggest problem I find is the tiny IDC connectors carrying the two wires from the RCA connectors to the Tank's transformer terminals. They fail with the greatest of ease. Tack-solder them back on after they do. The tanks take a real beating over time, stressing & breaking the lead wires between the RCA's and the tank's XFMR's...normally the fault when there's no Reverb anymore.
When I get thru all the JCM2000 series, then it's on to the JCM900's. Similar rear panel PCB problems on those as with the 2000's.
Caught what? SOLDER FRACTURES. The Rear panel PCB assembly on the JCM2000 models, be it the TSL, the DSL50 & DSL100's all use the same board layout. What I find on EVERY one of these amps from constant road use is radial solder fractures around the Impedance Select Switch for staters. That's OPEN circuit on the OT....no output, while you're driving the amp open circuit. Also, the SPEAKER OUTPUT JACKS. 80% of what I've just gone thru....radial solder fractures on those as well.
There is a certain satisfying attribute to solder fractures, where it sometimes works and sometimes not....you can give the amp a big SLAP on the top, to wake it back up!! Until it stops again.
On the TSL, I've never seen one come in WITHOUT fractures on most of the 8-pin DIN Footswitch connector. Last one, every contact was fractured. Eh...didn't need the foot switch anyhow. XLR Direct Out....ALWAYS fractues on those contacts.
The +/- 15V supply dropping resistors.....fractures on those most of the time. AND, the Effects Loop jacks.
I.E, ANY of the REAR PANEL JACKS & HARDWARE that are used to support the PCB assembly......Marshall's engineering staff seems to believe (as so many other MFGR's do) you can support PCB's by their solder connections of panel mounted parts. Don't need no stinkin' mechanical support brackets that raise the cost half a buck! HAH!
The AC Mains board assy.....50% of those had radial fractues around the IEC 320 AC Mains connector, and many also had fractures on the AC & HT fuse posts.
Getting at the Bias board on these amps.....ya gotta pull the main PCB up to extract it. But, before getting to that, I had 25% of the power tube sockets with solder fractures. Sometimes had them on the filter caps, periodically on the elevated Screen & supply 5W resistors. All the rest of the parts on those boards...rarely find faults, as far as solder fractures go.
The bias board....all too often, radial fractures around one or more of the pot leads. (While I'm on those boards, I'll seep in some Caig DeOxit into the pot, and exercise it, then re-set it where it was for a starting point when it's powered back up). And same on the 7-pin connector, as well as on the 3-terminal header used for DMM connections externally.
De-solder, THEN Re-solder. NOT just add solder.
On the front panel boards, for starters, all the pot hardware is finger tight, if not already coming off. Most always solder fractures on the INPUT jack. The front panel pots....they do use a 2-point support bracket....BUT....Marshall's layout staff only used the thinnest Annular Ring around those tabs. Try and de-solder & re-solder to solidify those support tabs......you just broke the adhesion of the annular ring to the PCB!! Hate it when non-service folk do board layouts! You're etching all that copper (full sheet of it) and flushing it down the drain, when you COULD lay in substantial land area to anchor components to.
The small Reverb board over in the front left corner is usually ok.
The Reverb Tanks....biggest problem I find is the tiny IDC connectors carrying the two wires from the RCA connectors to the Tank's transformer terminals. They fail with the greatest of ease. Tack-solder them back on after they do. The tanks take a real beating over time, stressing & breaking the lead wires between the RCA's and the tank's XFMR's...normally the fault when there's no Reverb anymore.
When I get thru all the JCM2000 series, then it's on to the JCM900's. Similar rear panel PCB problems on those as with the 2000's.
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