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Early Marshall DSL50 JCM2000 issues
Early Marshall DSL50 JCM2000 issues
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Old 12th March 2020, 02:35 AM   #1
jimmy74 is offline jimmy74
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Default Early Marshall DSL50 JCM2000 issues

I have an early version of the DSL50 jcm2000 amp to which there is no reference anywhere...printed out the schematics I could find but there are too many differences in denomination of the components and wiring lugs. Anyways I'll state my findings, initial problem is that the channel switching doesn't work at all, the LED doesn't turn on either...so basically its stuck on the clean channel. I tried powering up the amp just to see if it was working at all...it does sound very flimsy and bad so powered off and proceeded to do some tests. HT, heaters and bias voltage seem to be ok. It's just the LV that seems dead. So tracking from the PT LV lugs I'm getting around 21vAC through to the rectifier diodes D6, D7, D8 and D9. On the other sides of D8 and D9 I'm getting around -58vDC and on the other side of D6,D7 I'm getting 0. So I replaced them but still the same readings.
So my question at this point is... am I getting the right AC readings off the PT? If so, since the amp has obviously been tampered with in the past by someone else, did they solder the PT LV wires to the right lugs on the board? W9, W10 and W11 are the lugs used on the board but on the schematic these lugs are denominated W11, W12 and W13. There are other proven factory differences between the board and the earliest schematics so for that side of things I think everything is fine. The other difference I noticed are C6 and C37 are on the board both electrolytic (they have been replaced with 10uf 450v) which I guess is incorrect as C37 on the schematic states 47uf 63v so again too many inconsistencies to be able to rely on any versions of the schematic.

thanks for any help at all
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Old 12th March 2020, 08:01 PM   #2
Enzo is offline Enzo  United States
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What schematic do you have and which do you need?

Did you contact Marshall directly and ask if they could provide them?

I am looking at issue 3 1997.

meanwhile, why are we throwing all these parts into it? -58v looks like a reasonable bias supply to me.
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Old 13th March 2020, 09:02 AM   #3
jimmy74 is offline jimmy74
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Update: found the problem...compared the readings to another jcm2000 dsl50 and readings were more or less the same except the lv readings on the output board. I managed to trace back to the 2 pcb mount fuses so I replaced them and the amp is back to working conditions....however I still would like to know what made them blow.
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Old 13th March 2020, 11:43 AM   #4
JonSnell Electronic is offline JonSnell Electronic  United Kingdom
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The 6A3 fuse is the heaters and the other is HT. Doubtful they failed together with the same cause.
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Old 13th March 2020, 11:56 AM   #5
jimmy74 is offline jimmy74
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No the small pcb mount fuses on the output board
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Old 13th March 2020, 12:32 PM   #6
JonSnell Electronic is offline JonSnell Electronic  United Kingdom
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If they are 6A3 then they are for the valve heaters.
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Old 14th March 2020, 11:35 PM   #7
jimmy74 is offline jimmy74
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They're the small black plastic enclosed pcb mount fuses on the output board 250mA for the lv and switching supply
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Old 15th March 2020, 08:01 PM   #8
Tarzan is offline Tarzan  Belgium
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On each pcb is a code, something like: DL50-61-00 or DL50-60-02 or ...
What are the codes on yours?
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