This is the best video on this subject, imo. I have DSL50 built in 2000 with a rev 5 mainboard. After watching several vids and reading, I did the "air gap" fix on the power tubes along with swapping the 220K stoppers for 5.6K, and it helped a lot, but it was still a little bit unstable on the right power tube (when looking in the back) after an hour, while the left tube was mostly stable. So I took it back apart and also did your excellent "cap lift" fix at the end of the video, too. This sucker is now rock solid even after hours of use and bias does not budge one bit. And the amp sounds magnificent now. Amazing how ratty it sounded with the 220K and the wandering bias... Thanks so much for sharing this info, just goes to show these amps can indeed be fixed right for under $1 in parts and some elbow grease. BTW, Amazon has the 5mm diamond hole drills for just a few $. They work perfectly for doing the air gap part. Low speed drill is best.
I am glad it helped you. This is why I have this channel. I get a lot of grief from "experts" but who cares about their opinions. I have been doing amp work for decades, and have seen a LOT of issues. Thanks for watching, and the nice comment. Don't be a stranger, check it out occasionally.
Its amazing how they took amplifiers from point to point printed circus boards and they are more expensive. I build my own amplifiers out of 1950s and 60s PAs, gut them and put my own components in, simple, they sound great. All point to point, no crappy circus boards
I agree. Problem here is in the age of point to point, labor rates were much lower. Point to point also takes more skill to do properly. Also point to point is a wonderful thing but with modern amps with multiple channels, channel switching and other bells and whistles, point to point is pretty much impossible. Plus throw in design /layout issues we have a mess. Thanks for watching.
I am encouraged by your confidence with your solution to this BS issue that Marshall has bestowed upon a legend. Just by the fact that you produced a vid explaining your solution should make me hesitate to ask you a searing question. Any way I must ask… have you had any returns with the very same run away bias issue after your services? I have replaced several boards over the past decade along with a couple other attempts as found on the internet. Had a couple returns with the same failure and lost a couple clients as well. Thanks for the vid and your response. Mark
Thanks for the kind words. My answer will be short. Nope, not a single return on the bias drift issue. And I have done quite a few. Mainly because I removed the bias circuit completely away from the high positive voltages. I believe there are a couple more videos here on the same subject. Thanks for checking out the video.
Sadly, most did not have this knowledge over 20 yrs ago when the 2000s were born. Most of the amps failed after years of use. Plus, it was their flagship amp. People were impressed by them and they were put on stages all over the world. They had to be good, they were a Marshall!
"Probably just a tube", "Probably just a loose wire", and "Is it done yet?" I'd rather hear nails on a chalkboard than have to hear any of those phrases ever again.
Yep, not unlike...." make the action as low as you possibly can without buzzing" .....and my new favorite from the new generation.... "Can't you get an app to tell you how to fix it?"
There is no component failure that causes this, it is voltage leakage between traces of the PC board. Here is another from this channel. ua-cam.com/video/ZTxdRewopkM/v-deo.html
Nicely Done. I have one of these on the bench for an effects loop issue. Do you feel this should be done to any jcm2000 dsl or is it uncommon enough to gamble with. Its a 1998 model year.
It would not be a bad idea. I have seen this a lot. I feel it is just a matter of time. The story is they had a board problem... I think it was more a layout problem. I have a problem with circuit boards and high voltages in close proximity. Don't even get me started on the high amperage current on the heaters... :)
I have a 1997 DSL50 that i actually had you service once ( main input came off the board). But i recently had it die on me again. While playing it, the HT fuse popped. I removed the power tubes and ran a quick bias test, but whats happening is crazy: the left bias adjustment is working the right tube ( V7) and the right bias adjustment is working the left tube (V6). The pots are change the voltage but if you dial them all the way left ( so counterclockwise), you get -25.5VDC, while dialing them all the way to the right ( clockwise) it maxes out at -33.3VDC, so well below what you'd need to bias this right ( between -36 to -45VDC according to Marshall at least). Is THIS a bias drift?
Hi Mike! I remember that, seems like a few years back. Ok question one..... the bias controls work correctly they do control opposite sides. As for bias drift, Usually one or both sides of bias will drift positive as the amp runs. I have no answer for the low bias without checking it out myself.
This is the best video on this subject, imo. I have DSL50 built in 2000 with a rev 5 mainboard. After watching several vids and reading, I did the "air gap" fix on the power tubes along with swapping the 220K stoppers for 5.6K, and it helped a lot, but it was still a little bit unstable on the right power tube (when looking in the back) after an hour, while the left tube was mostly stable. So I took it back apart and also did your excellent "cap lift" fix at the end of the video, too. This sucker is now rock solid even after hours of use and bias does not budge one bit. And the amp sounds magnificent now. Amazing how ratty it sounded with the 220K and the wandering bias... Thanks so much for sharing this info, just goes to show these amps can indeed be fixed right for under $1 in parts and some elbow grease. BTW, Amazon has the 5mm diamond hole drills for just a few $. They work perfectly for doing the air gap part. Low speed drill is best.
I am glad it helped you. This is why I have this channel. I get a lot of grief from "experts" but who cares about their opinions. I have been doing amp work for decades, and have seen a LOT of issues. Thanks for watching, and the nice comment. Don't be a stranger, check it out occasionally.
Its amazing how they took amplifiers from point to point printed circus boards and they are more expensive. I build my own amplifiers out of 1950s and 60s PAs, gut them and put my own components in, simple, they sound great. All point to point, no crappy circus boards
I agree. Problem here is in the age of point to point, labor rates were much lower. Point to point also takes more skill to do properly. Also point to point is a wonderful thing but with modern amps with multiple channels, channel switching and other bells and whistles, point to point is pretty much impossible. Plus throw in design /layout issues we have a mess. Thanks for watching.
Air is a great insulator.
One of the best!
I am encouraged by your confidence with your solution to this BS issue that Marshall has bestowed upon a legend. Just by the fact that you produced a vid explaining your solution should make me hesitate to ask you a searing question. Any way I must ask… have you had any returns with the very same run away bias issue after your services?
I have replaced several boards over the past decade along with a couple other attempts as found on the internet. Had a couple returns with the same failure and lost a couple clients as well.
Thanks for the vid and your response.
Mark
Thanks for the kind words. My answer will be short. Nope, not a single return on the bias drift issue. And I have done quite a few. Mainly because I removed the bias circuit completely away from the high positive voltages. I believe there are a couple more videos here on the same subject. Thanks for checking out the video.
People should refuse to buy these junk amps. Get a handwired or take piano lessons.
Sadly, most did not have this knowledge over 20 yrs ago when the 2000s were born. Most of the amps failed after years of use. Plus, it was their flagship amp. People were impressed by them and they were put on stages all over the world. They had to be good, they were a Marshall!
"Probably just a tube", "Probably just a loose wire", and "Is it done yet?" I'd rather hear nails on a chalkboard than have to hear any of those phrases ever again.
Yep, not unlike...." make the action as low as you possibly can without buzzing" .....and my new favorite from the new generation.... "Can't you get an app to tell you how to fix it?"
I have a 100w 2000 dsl in need of repair, same issue I have the revised board and new matched power and preamp tubes I live in the beckley area.
Sorry to hear that. I must mention I am not a fan of the new boards.
@@guitarc.p.r.9675whys that man?
I missed what was the initial component that failed to cause the thermal run away?
There is no component failure that causes this, it is voltage leakage between traces of the PC board. Here is another from this channel.
ua-cam.com/video/ZTxdRewopkM/v-deo.html
@@guitarc.p.r.9675 I see, I get it now. Thanks!
Nicely Done. I have one of these on the bench for an effects loop issue. Do you feel this should be done to any jcm2000 dsl or is it uncommon enough to gamble with. Its a 1998 model year.
It would not be a bad idea. I have seen this a lot. I feel it is just a matter of time. The story is they had a board problem... I think it was more a layout problem. I have a problem with circuit boards and high voltages in close proximity. Don't even get me started on the high amperage current on the heaters... :)
Can i send you my 1996 jcm 900 model 4500 to be properly lookked at i have a loss of volume
We can discuss that if you feel the need.
I have a 1997 DSL50 that i actually had you service once ( main input came off the board). But i recently had it die on me again.
While playing it, the HT fuse popped. I removed the power tubes and ran a quick bias test, but whats happening is crazy: the left bias adjustment is working the right tube ( V7) and the right bias adjustment is working the left tube (V6). The pots are change the voltage but if you dial them all the way left ( so counterclockwise), you get -25.5VDC, while dialing them all the way to the right ( clockwise) it maxes out at -33.3VDC, so well below what you'd need to bias this right ( between -36 to -45VDC according to Marshall at least).
Is THIS a bias drift?
Hi Mike! I remember that, seems like a few years back. Ok question one..... the bias controls work correctly they do control opposite sides. As for bias drift, Usually one or both sides of bias will drift positive as the amp runs. I have no answer for the low bias without checking it out myself.
Hollywood had Howard Dumble...we still have C.P.R. Charlie. Lucky us.
I am no Alexander Dumble, but thanks for the nice comment.