Marshall DSL 50 and 100 last hope

[booj]

Just got in two amps. Both of the rats nest type models. The 100 was deemed "unrepairable" and was offered to me to fix. the 50 was labled as "nothing but trouble since I got it". What I'm asking is for any tips on making these things go away as fast as possible. I can get new boards if that's what it takes, depending on the cost of course. I'm sure these guys will take some time, but I want to put them out there on the forum in case some other poor sucker...er ahem unfortunate tech, gets one of these. Give me a shout out if you have had an experience with one or both of them so SI can get a grip and get started in the right direction! I'll keep y'all informed as to progress along the way. and....begin...

[Enzo]

"unrepairable"??? It is just a tube amp. Most of us can draw a working schematic on a bar napkin. And that is no particular pat on the back.

Note that those two problem descriptions tell us excactly nothing about what is wrong with either amp. Without specific complaints, it is darn hard to give any tips. But asking for tips assumes whatever might be wrong with yours is exactly what was wrong with someone else's.

I suggest forgetting the editorials and just look into each amp for what it needs, then do what it takes to fix it.

The only unrepairable tube amps I ever saw were ones needing transformers or other expensive parts that made it cheaper to just buy a new amp. Circuit problems are correctible.

[Mick Bailey]

I start of by looking what the market value of each amp is in working order. Sometimes poor cosmetics can seriously devalue an amp - always consider that a really beat-up but working amp is never going to be worth a great deal. After a good visual inspection I determine whether the transformers and power supply are working, and do a quick list of what the amp may need - new tubes, recap, maybe some miscellaneous repairs. This gives me some idea of the cost to fix and final value.

Sometimes this doesn't work out well for low-end far-eastern amps. But most Marshall amps are economical to repair, well understood and documented. With the DSL100, you need to look at the manufacturing year and main PCB revision. This will tell you if it's one of the 'problem' boards.

[Alex R]

I think you're in the UK - in which case it is well worth trying to get recognised as a repairer by Marshall, they will then sell you parts wholesale, including new boards for these amps.

The reason they might need a new board is that the older ones, which are a paler green with no fibreglass weave visible under the surface, can get conductive and produce overheating of output tubes. Generally when people say a JCM2000 amp is 'nothing but trouble' it is output tube overheating caused by conductive boards. The fibreglass boards now supplied don't have the problem, they are a darker, slightly translucent green and the weave is visible under the surface.

To test an old-type board fire it up with the chassis open, clip a voltmeter to a pin 5 or somewhere so you can watch the bias voltage, and blow some hot air at the power tube area, if the bias voltage starts to drop you need a new board.

There are still some online sources recommending dremelling around the output tube pins etc. Not a good fix as the whole board is potentially a problem and there is no easy way to be sure where it is conductive and where it isn't.

Other common faults are the little cap on the power tube plates starting to burn up - just removing them is a fix or replace with 2000v types; also the pair of caps that run to the mute switch can be an issue. Otherwise they are reliable amps, always repairable.

They look like rats nests but if you mark up the little white connectors when you remove them (I use a fine point indelible pen) you won't go wrong.

[Mick Bailey]

I always replace the early boards if the amp has problems. Given the labour cost and the need to guarantee the amp, it doesn't make economic sense for me to do anything else. Some of the original (1998?) production run are still going strong, though. One thing to watch for is the bias board, too. I've seen many of those with bad solder joints and/or bad pots. I replace the pots and resolder the board when I get these in for repair.

[TimmyP1955]

Give this a look:

[catstrat]

Bias drift

There was another repair I use on the TSL 100 but it has pin 5 being isolated from the board. Someone said a Marshall engineer thought of that. This type of a repair may look involved but it's really not. I just desoldered and remove the output sockets and use a counter sink bit to drill out the hole. That type of a bit gives me a prettier hole than a drill bit. I usually drill it to 3/16 or even 1/4. Just enough to make sure the socket pin does not touch the board. Then the grid stoppers I use a metal film and I solder one end to the socket pin. I've fixed 4 or 5 tsl and every owner says it fixed the problem. But the fix Timmy posted is one I'll try next time. It sounds like a better way to do it. Some replace bias voltage filter caps, bias resistors, trim pots, but that's up to you. Good luck.

[Leo_Gnardo]

Marshall DSL 50 and 100 last hope

Booji wan Kenobi, you're the only one who can help us!

Couple of weeks ago one of our MEFsters mentioned a hollow drill, meant for use on ceramic tile, about $16 at your friendly Home Despot. Looks like it should make this operation a lot easier. Up 'til now I remove the output tube sockets entirely, drill thru the pin 5 pad, and reassemble. Earlier I Dremeled around the pin but every time the grinder tip hits the pin, it's easy to lose control & also beats up the electrode threatening to break it off.

FWIW I use carbon comp stopper resistors, 5K6 as in standard Marshalls. 220K as Marshall has it in this amp, what were they thinking?

Definitely makes sense to examine the bias card & fix if necessary.

[booj]

Excellent information, and the kind of help I was looking for! I thank you most heartily timmyP1955!

[booj]

Excuse me. I didn't say they were unrepairable. I said they were "deemed" unrepairable by the person(s) giving themn to me to fix. Other techs had given up on them. I just wanted to get some pointers before I dug in. I naturally panic when something troublesome comes along. Why do you even answer these posts if you have nothing to say?

[booj]

Thanks for the info. I'll so that.

[booj]

Again;, thank you very much for the info. Makes it a LOT easier to get a grip on this stuff. I'm 20 minutes east of St. Louis.

[booj]

couldn't agree with you more about the 220k resistors. No sense to me at all. Thanks for the info. It will help greatly if I need to "go in with a drill"

[Enzo]

Why do you even answer these posts if you have nothing to say?

Sorry I interfered with your effort, I'll not do it again.