Marshall SC20H weird problem! I am getting desperate so please help...

Discussion in 'Marshall Amps' started by CroTone, Mar 4, 2021.

  1. CroTone

    CroTone Active Member

    Joined:
    Nov 24, 2019
    Messages:
    85
    Likes Received:
    139
    Hello guys! Here I come again with another streak of bad luck...

    So...I've just got a new SC20H...plugged it regularly from the 8-ohm speaker output to an 8-ohm speaker cab by using a high-grade speaker cable. The thing does not make a sound! I put preamp at the half and then slowly started raising the volume. No sound was coming out of the amp until I really struck the chords very strong and then some weird distorted buzzy sounds of loud volume start to come out...no normal tones. The same is if I do the low input or high input, except when it is on high input this bad sound is much more distorted (again), and on the low input is more towards the cleanish sound.

    What is really crazy about it, I noticed that when I go to switch the amp off on the power button, by not transitioning from standby but going straight off from say high mode... then those chords that I've just played are heard and start to sound normal - this happens only when I hold the power switch in between ON and OFF...kinda stuck in the middle. I noticed this because the sound started to appear normal for the blitz of a second when I was shutting the amp down. And when it got shut down on the off switch it still rang a bit of those chords but seemed to me it was a normal sound there. Now does any of you know what a hell is this and what this means?

    I've never encountered this problem before.

    Also if I might add, no weird smell, flames, or whatever occurred. Tubes seem to glow normally, amp powers up normally.

    I have an Origin 50 that normally works with this same cabinet and the same cable connection, just tested it after this.

    This is my 2nd faulty Marshall in the row and I honestly can't believe it...I am really desperate and afraid I am going to have to return this one as well.
     
    Dean Swindell and tce63 like this.
  2. dju

    dju Member

    Joined:
    Jan 13, 2011
    Messages:
    87
    Likes Received:
    45
    Location:
    Texas
    I'm reaching here and maybe since I don't usually use the effects loop I may be way wrong. but what is the effects loop set to? if it is a serial effects loop and there is nothing in the loop then that would in theory disconnect the preamp from the power amp section. just a thought for your possible problem.

    dj
     
    Old Punker, tce63 and JamminJeff like this.
  3. JamminJeff

    JamminJeff Well-Known Member

    Joined:
    Feb 27, 2021
    Messages:
    203
    Likes Received:
    428
    Not being in the room, this is a great first diagnosis. In theory, the Effects Loop is in between the pre-amp and the power amp. In bypass, it shouldn't be in the signal path. When inserted into the signal path, any other input (effect, etc.) then becomes part of the signal chain.

    Either way, the Effects Loop, regardless of settings, shouldn't affect the final output to your speaker cabinet or any output.

    Did you test the DI for output ?
     
    Jethro Rocker, Old Punker and tce63 like this.
  4. CroTone

    CroTone Active Member

    Joined:
    Nov 24, 2019
    Messages:
    85
    Likes Received:
    139
    Guys, I am not having anything in the FX loop and the FX loop switch is OFF on the back of the amp.

    I can't even troubleshoot where the possible problem is.

    I turned the amp on again, it powers up and all lights are there, I did not encounter any popping noise, fuse blow-out, any weird smell, or anything of that kind.
    Upon visual inspection of the back, I see both power amp tubes glowing as well as the preamp ones.

    I plug in the guitar in the high input jack, set the preamp gain at noon, and set the volume at 3' o clock. No sound gets out with the normal type of playing.
    However, if, at the same setting, I struck a power chord really really hard some sound starts to get out of the speaker.
    It is a nasty, distorted, unhealthy type of sound like the speaker is cracking, it does not ring out and goes out abruptly without fading.
    The same is on both "high/low" attenuation settings and on both low/high input jacks.

    I am utterly dissapointed. This is the 2nd Marshall in a row that I have serious issues with.
     
    tce63 likes this.
  5. JohnH

    JohnH Well-Known Member

    Joined:
    May 31, 2008
    Messages:
    4,391
    Likes Received:
    2,435
    Location:
    Wilton NSW
    If its new, back it should go!
     
  6. CroTone

    CroTone Active Member

    Joined:
    Nov 24, 2019
    Messages:
    85
    Likes Received:
    139
    It is new, but...I am scared if I would make an order of another one instead of this one or should I just get my money back.
    2 Marshalls in the row, out of the box, that did not work for me...it is a streak of bad luck that I never experienced before. Anyone else had such experiences, two in a row? I feel like I am the unluckiest motherf'cker out there...
     
    tce63 likes this.
  7. RCM 800

    RCM 800 Well-Known Member

    Joined:
    Dec 20, 2019
    Messages:
    874
    Likes Received:
    1,755
    Send it back. Shit happens. See if they can test the next one going out.
     
  8. RCM 800

    RCM 800 Well-Known Member

    Joined:
    Dec 20, 2019
    Messages:
    874
    Likes Received:
    1,755
    You could also check the pre amp tubes. Just because theyre glowing doesnt mean they’re working.
     
  9. JohnH

    JohnH Well-Known Member

    Joined:
    May 31, 2008
    Messages:
    4,391
    Likes Received:
    2,435
    Location:
    Wilton NSW
    it does sound really unlucky about what should be a great amp. They need to replace it for you at no cost to you, but contact them to discuss and arrange the return.

    Used to be easy to sort these things out with real bricks n mortar shops.
     
  10. Old Punker

    Old Punker Well-Known Member

    Joined:
    Jun 17, 2020
    Messages:
    870
    Likes Received:
    2,160
    Location:
    Ontario, Canada
    This is actually the first time I've heard of a problem with a new SC20H. Mine has worked perfectly since I got it. Do you have spare power/preamp tubes around to test the tubes? It is possible that a tube got damaged in shipment, from physical shock, since everybody seems to ship gear with tubes installed.

    I had a brand new power tube short out in my attenuator after only 2 months of occasional light use. It happens.
     
    tce63, scozz, Maggot Brain and 2 others like this.
  11. CroTone

    CroTone Active Member

    Joined:
    Nov 24, 2019
    Messages:
    85
    Likes Received:
    139
    I don't want to tamper with that due to warranty issues, etc. thought
    Yes, it will be a drag to send it back because the shop is in another city but they did arrange dispatch return service at their cost the first time and offered an alternative.
    They will be surprised once I call them again tomorrow. I was looking forward to this amp so much but it obviously was not meant to be...again.
    Either I try for the third and last time or I just give up on the idea of adding another amp to my collection. Quality control seems to really be the issue here.
    I had some problems with used amps in the past, but that is what is to be expected...replace tubes, do some small fixes here and there, change electrolytes and a few capacitors, etc...but the things used to work. Never had I experienced some really major flaws except in one Laney amp for which I had to change the output transformer.
    Now I am getting new stuff wrapped into bubbles, I plug it in and it does not work. I don't know what to think anymore. It is crazy shit for sure.
     
    tce63 and Old Punker like this.
  12. fitz288

    fitz288 Space-Time Curver Silver Supporting Member

    Joined:
    Apr 7, 2020
    Messages:
    1,459
    Likes Received:
    3,074
    Location:
    Pittsburgh, PA
    I wonder if you got the same one twice?
    Take a pic of the serial # before you send this one back.
     
    tce63, scozz and Old Punker like this.
  13. marshallmellowed

    marshallmellowed Well-Known Member

    Joined:
    Jun 26, 2009
    Messages:
    4,463
    Likes Received:
    6,423
    I agree, sounds like a preamp tube, if not that, try putting a jumper in the effects Loop, with the effects loop on.
     
  14. RCM 800

    RCM 800 Well-Known Member

    Joined:
    Dec 20, 2019
    Messages:
    874
    Likes Received:
    1,755
    Might not be the shops or marshalls fault, might be the guys hauling your stuff tossing it around like a dodge ball.
     
  15. pedecamp

    pedecamp Well-Known Member

    Joined:
    Dec 7, 2009
    Messages:
    16,610
    Likes Received:
    15,390
    Turn on the effects loop and plug your guitar into the return, if you get sound your power tubes are good and you probably have a bad preamp tube, replace the preamp tubes with a known good tube one at a time (grab one out of your ORI50 if you have no spares) to figure out which is the bad tube. If none of this works send the amp back for a replacement.
     
  16. RCM 800

    RCM 800 Well-Known Member

    Joined:
    Dec 20, 2019
    Messages:
    874
    Likes Received:
    1,755
    ^^^^^^this.
     
    Maggot Brain and Old Punker like this.
  17. Old Punker

    Old Punker Well-Known Member

    Joined:
    Jun 17, 2020
    Messages:
    870
    Likes Received:
    2,160
    Location:
    Ontario, Canada
    I am a little confused. Is this the second new SC20? Or did you order a different amp model the first time?

    If this is your second defective SC20, what was wrong with the first one?
     
    tce63, scozz and fitz288 like this.
  18. Old Punker

    Old Punker Well-Known Member

    Joined:
    Jun 17, 2020
    Messages:
    870
    Likes Received:
    2,160
    Location:
    Ontario, Canada
    Yeah, you never know...

    [​IMG]
     
    tce63 likes this.
  19. CroTone

    CroTone Active Member

    Joined:
    Nov 24, 2019
    Messages:
    85
    Likes Received:
    139
    Dude, I am going to make a statue in your honor.
    OK, so I did this.
    Plugged the guitar into RETURN, turned the button for FX loop ON, played a few notes...the sound is there! It's coming out as normal as I should expect it!
    The preamp is set half-way and the volume is on about 3. Sounds completely normal.
    Now what? Should I open it up and start replacing preamp tubes? In which order, which one is likely to be the culprit? No spare tubes, I only have one from Origin.
    What do you think? Do I stand a chance saving this amp?
     
  20. CroTone

    CroTone Active Member

    Joined:
    Nov 24, 2019
    Messages:
    85
    Likes Received:
    139
    Now, this isn't 2nd SC20. It is my first SC20, the first one that was wrong was DSL20HR.
     
    Old Punker and tce63 like this.

Share This Page