Marshall DSL100 replacement boards

[g1]

Just for reference, this link was posted in another thread, they have replacement boards for DSL and TSL. (thanks SteveJ)
MarshallDSL100 Main Board (Original Marshall Part) Hot Rox UK

[John G]

Hi,
I have been working on a DSL50 dated 1999.
The owner has had it tucked in the wardrobe for a few years and unfortunately decided to get me to repair it. The fun started when the bias drift problem showed up.
I did my Telegraph pole wiring mods (I lift all the components including the phase spliter caps and components that feed the o/p tubes grids, and string them all together with insulated wire above the board ) and that problem was solved.
I then noticed a Hum after about 10 mins coming from the preamp both on the clean and distortion chs. I removed fuse F2 and inserted 6.3 volts DC from my bench isolated PSU. The hum had gone and was still quite after half an hour. The DC is now feeding all four pre tubes. This thing is so quite I can hardly notice it is on.
The DSL100 is harder to implement as F2 also feed one of the EL34s .I will try to dc only the first three tubes and see if the Hum reappears.Cheers
John

[John G]

Hi,
Just an update since my previous post.
A correction first, the Fuse I lifted was in fact F1 not F2.
I extended the DC heaters to include V3 even put a heat sink on top of the BR1 bridge rectifier, intalled the fuse F1 and turned it on...............Silence.
After about 10 mins the hum was back loud as ever, Dam it !!
So I them cut the traces to V4 pins 4/5 and 9 and ran wires removing some of the possibility of board leakage. Still no improvement.

I dug out a large metal bridge rectifier and connected it to W9 and W10 (heater windings). I removed BR1 rectifier from the board and installed two links in its place, I isolated the W9 trace feeding the removed bridge (BR1) and connected a long insulated wire ( for the -dc from the new bridge) long enough to reach the new rectifier sitting on the chassis in between the pre board and the STBY switch area. The +dc was attached to the F1 fuse clip closest to the back.
Turned it on, silence...............after half an hour still silence.
I need to tidy things up and test some more.
I will post an update later.
Cheers,
John

[keepfixin]

Hi there, first post here and wanted to blab about my thing. I am a full time tech with adequate skills and had the drifty bias situation and it took me awhile to get my act together since the endzone fix seemed elusive.
I did the pin 5 isolation and the resistor fixes etc but didnt remove the -v completely so it failed. Tried a new CE dist board (the non Rohs was 4 bucks cheaper!) and thought I was all set but decided to let the thing heat up for 90 minutes, and it drifted. Did more reading and came across DR Tube, got his nifty kit and yes I got the original board up fine. So I started to wonder why CE (or anybody else) would have these funky old (meaning non corrected) boards for sale. The contradiction came from fellows who bought UK vendor sourced stuff and had reported success right away. The old board that I stabilized still had the clean channel hum so I was hesitant to say that I really fixed it. Can't recall that I heard bad hum way back then and the customer didnt mention it either. I have had the thing in the shop for many , ahem, months.
I think CE is cool but they admitted that there are no techs available to discuss stuff on the phone. I have been waiting for their email to see if Marshall would be ok with a return in my favor on that "new" board. I bought two of the Dr Tube mod boards so I can salvage the thing for an ebay auction, and may still feel shady in the process. I would be condifent in the bias fix but will not make the effort to test it for any hum issues.
The original setup is in the headbox but I am viewing the newer thing here, it is JCM2-60-00 with a sticker reading TL10-60-02-01-S. It does look different and "new" but I am too lazy to go into details about resistor specifics etc.
I am satisfied with my lessons learned and just wanted to encourage someone to not waste too much time on this. Time is better spent writing more song dittys.

BB