Now I'm angry! SteveD, your thoughts please?

[Deputy Dawg]

Okay,

So I just posted a very short while ago talking about how delighted I was/am to have got my Vintage Modern back from the warranty repair shop - in 100 percent working order. You know, the effects loop, when engaged caused a drop in signal level. Well, I got a couple of hours of playing out of it when, all of a sudden, it's like someone turned the volume down to almost zero.

At first I thought I bumped the volume knob on my guitar. But no. I pushed the "loop" switch in back of the amp to its loop bypassed position and bam, the amps full level is back. Looks to me like the FX loop board has failed again. There must be something causing the replaced FETs to "blow"..... Power supply issue? Shorted trace on PC board? Out of spec'd part up/downstream?

Tomorrow I am going back to my local shop and lobby very strongly for a brand new VM. I obviously got a "lemon". I am NOT ready for another month in the shop waiting for parts from Toronto that may well fail again... (I wonder if the stocked FETs used for warranty repair are from the same batch used in the manufacturing "run")


Deputy Dawg :evil:

[SteveD]

Fets are notoriously sensitive to static discharge and hence need to be handled with the proper protocol. If by any chance these handling precautions weren't observed by the repairer then they could have been damaged.

I am assuming that there is nothing wrong with the device/s that you are running in the FX loop, no safety earths diconnected from rack stuff etc.

Pain in the arse I know. :(

[Deputy Dawg]

SteveD,

Thanks for your interest, help and your reply....

I had the same thoughts as you about the gear I have patched into the loop but I use (and have used) this stomp box - an Electro-Hamonix Holy Grail Plus - in other amps effects loops with no problem. No possible ground issues as I am simply using unbalanced guitar cables to connect it. Could I test my outboard reverb unit in any way to rule it out?

I am looking at the repair invoice and it indicates that they changed out 2 part number: TN2404KL transistors (Steve, do these sound like the potential bad parts?)

As I indicated below, the amp worked for a couple of hours then, with no warning, the output level dropped to almost nil. Upon bypassing the loop by using the push-button in the rear of the amp, the level was restored.

Steve, do you think some other parts should be changed out as well? Would you recommend changing out the entire FX Loop/Reverb boards? I wonder if FETs damaged by static would work for a while, then fail. (I would think that they would not function at all after being damaged). What other parts could affect these FETs?

I know if I send the amp back for warranty repair that it will be gone for a month or more again. So I want to be sure it is fixed. Should I implore them to change out the FX and reverb assembly? Are the replacement FX/Reberb boards from newer batches with more dependable parts?

I know these are some tough issues but I hope you and Marshall will stand behind what is a wonderful sounding amp and help to salvage what has been an ongoing nightmare of a first experience with a Marshall product.

Thanks in advance for any assistance you may give me SteveD.

Deputy Dawg (Randy in Canada)

[SteveD]

The two TN2404 are indeed the high voltage fets and they are static sensitive. Also, it is possible for them to be damaged through improper handling protocol and fail at a later date, sometimes hours, days, weeks or months.

It's not possible for me to say if there are any other problems without having the amp in front of me but if they had the Marshall service documents then they would have verified the whole circuit I would have thought.

There are no batch or part issues with these components, you are simply having bad luck. It may even be you if your room is prone to static where your equipment is set up.

I doubt it would take another month to change those fets again unless they only ordered two. :)

[slowpokerhino]

Since your amp is functional without the loop. If they do need to order 2 more I'd get them on it and not bring in the amp until they get them. That will cut your down time dramatically.

[hedas46]

I've just bought a Vintage Modern head and my volume drops considerably when I engage the effects loop and I was told in the shop that this was normal for this amp so I am using a EQ pedal to boost the volume. I only use a bit of delay to fill the sound. Do you recommend I return the amp to the shop for repair.

[DeanM]

I've just bought a Vintage Modern head and my volume drops considerably when I engage the effects loop and I was told in the shop that this was normal for this amp so I am using a EQ pedal to boost the volume. I only use a bit of delay to fill the sound. Do you recommend I return the amp to the shop for repair.

that doesnt sound normal at all!!

[SteveD]

Welcome to the forum hedas46.

No it's not normal, probably the FETs problem. Return it for repair.