Marshall DSL 100 Low Gain Problem HELP!!!

[StudioX13]

first of all. this is my first post on this this forum so hello all!!! secondly, i apologize if this issue has already been addressed in the forums somewhere, i only searched for a short time.

PROBLEM:
scored a dsl 100 off ebay at a steal. (could be the source of this problem haha) the problem is on lead one and two the gain is VERY weak and badly broken up sounding starting at twelve o'clock and gets worse past that. I am very familiar with dsl's and know what kind of gain they are capable of. (alot!)

Solution attempt #1
instinctively thinking it was a preamp valve problem, i had them replaced. as well as the power tubes (also re-biased) ...same problem. also, i ran the pre from another dsl through my power section, sounded great... tons of gain. so that narrows it down to the pre-section

Solution attempt #2
i took the dsl to a certified marshall tech here in SC. he is obviously not a guitar player bc the result was "the amp is running at full power." said that he could find nothing wrong.

SO...
i am at the mercy of you guys. i cannot afford to ship it to marshall. My life is not complete without my DSL. what could be causing this low gain issue? PLEASE HELP!!!

-Chris Anderson
myspace.com/StudioX13

[izzybell2810]

Hi,
when you say the gain is weak, do you mean that the sound is cleaner or quieter than it should be?

[StudioX13]

The sound is much cleaner than it should be. Very little distortion at all.

[tim]

I'm surprised the certified tech didn't know about this: I've fixed at least a 1/2 dozen of these with this problem:


SYMPTOM: Low Ultra "B" Channel Gain. This problem was originally found in DSL's manufactured in the week 49 of 1997. (ie: SR# 9749XXXX), but shown upsporadically in other weeks of manufacturing. The symptom is low gain in the ultra "B" channel, which will sound like the classic "A" channel but will have low gain.

CURE:

1. Locate optocoupler LDR3 on the valve PCB assembly.

2. Connect an ohmmeter across the two leads coming out of the top of the optocoupler.

3. Turn on the MAINS switch only and set the amp to classic "A" channel. You should read less than 2k ohms.

4. Switch the amp to ultra "B" channel and your meter reading should change to about 100k ohms.

5. Replace LDR3 if it does not fall within these specs.

You'll have to order the LDR / Optocoupler from Korg if you find the one you have is bad, or maybe someone here would have one they would sell you. I get mine through a place I use to work at that is an authorized Korg/Marshall repair facility. The Korg P/N is OPTO00001 and I think list is around $10. If you search on this number NSL-32H-004 through Google, you might find it elsewhere.

[StudioX13]

Thanks so much tim! I'll relay this info to the tech and hopefully get her breathing fire again. Thanks again!!!