Monster Marshall amp problems. Help!!! - Page 2 - UK Vintage Radio Repair and Restoration Discussion Forum

Boater Sam · 11th Jun 2017, 5:24 pm

Thanks to you, one and all, its fixed.

T104 being turned on pulled STBY down. Found R233 to be open circuit, not high. Replacing it causes T104 to behave sensibly and the zener holds the collector voltage to 14.9v max. Put all the plugs back in.

Now there is 6v on STBY. Seems a bit critical on voltage at STBY.
Feeding a signal in produces output on both channels.
Job done. Time to put it all back together and give it a test.

Difficult to tell which knobs to turn, with FX and 2 overdrives etc., I downloaded the manual, thanks, it helps to see which and when.
Amp produces a bewildering range of distorted outputs, suppose that's what guitarists want.

Its very awkward to work on, too many leads plugged in all over the place and you only get access to the back of the main pcb by removing it completely, but then of course you can't run it.

Its great to get help like this from forum members, long may we all continue.
Love you all,
Sam.

Top Cap · 11th Jun 2017, 5:38 pm

Well done Sam, yes I have had only one of these come my way, hope I don't get a second though with mine the fault was pretty obvious

Les

dryjoint · 11th Jun 2017, 6:09 pm

Hi Sam, yup WELL DONE! Always a bit difficult diagnosing faults "at a distance", but it's good to get it sorted and out of the way. Wonder why that speaker was disconnected though....anyway job done and that's what counts. At least you don't have the pain in the proverbial getting new TDAs for it.
Enjoy your cruising!

Station X · 11th Jun 2017, 7:34 pm

Well done Sam. You met the deadline.

Enjoy your boating.

Boater Sam · 11th Jun 2017, 7:54 pm

The speaker cables exit the speaker part of the cabinet via 2 holes below and behind the amp which is on a shelf on top, and plug into the amp with 2 jacks.

Unbelievably there are no strain reliefs on the cables! So the lead had been pulled up until the spade connectors came off the speaker.

I tied a knot in both inside the speaker box, it won't happen again.
It didn't seem to do the amp any harm losing a speaker though.
Just happy that the help I got from folk here solved the problem, I really haven't the space or time for these monoliths. It was only a freeby favour anyway.
Sam.

Refugee · 11th Jun 2017, 11:35 pm

Well done.
It sounds like that sort of stuff has gone the same way as everything else we find these days.

Boater Sam · 12th Jun 2017, 8:37 am

If by gone the same way you mean digital and difficult to work on, you are right.
There is very little ordinary electronics in this amp, most of the sound processing is DIL chips, the amps themselves are monolithic chips, and the ECC83 is a preamp token to "the valve sound".
All in I consider it to be an advertising farce as it is as removed from a valve amp as it could be, oh, apart from the one.
The front panel has a plethora of knobs to make the sound louder and/or even more distorted, lots of push buttons too.
A Vox AC30 was a real amp.
Sam.

Herald1360 · 12th Jun 2017, 12:35 pm

The Marshall is more of an audio processor than just an amplifier with its own particular distortion characteristics. IF it were well engineered, well made and decent service info were available then it would be perfectly fit for purpose, but that IF is a big one nowadays, unfortunately

Boater Sam · 12th Jun 2017, 8:01 pm

Just a little aside to round things off.
The ECC83 preamp valve, triodes in cascode, still can't understand why other than it enabled the magic word " VALVE" to be on the front.
On inspection, surprise! its a Russian valve! And it looks original too.
Curiouser and curiouser.
Sam.

11th Jun 2017, 5:24 pm	#21
Boater Sam Banned Join Date: Dec 2013 Location: Middlewich, Cheshire, UK. & Winter in the Philippines. Posts: 3,897	Re: Monster Marshall amp problems. Help!!! Thanks to you, one and all, its fixed. T104 being turned on pulled STBY down. Found R233 to be open circuit, not high. Replacing it causes T104 to behave sensibly and the zener holds the collector voltage to 14.9v max. Put all the plugs back in. Now there is 6v on STBY. Seems a bit critical on voltage at STBY. Feeding a signal in produces output on both channels. Job done. Time to put it all back together and give it a test. Difficult to tell which knobs to turn, with FX and 2 overdrives etc., I downloaded the manual, thanks, it helps to see which and when. Amp produces a bewildering range of distorted outputs, suppose that's what guitarists want. Its very awkward to work on, too many leads plugged in all over the place and you only get access to the back of the main pcb by removing it completely, but then of course you can't run it. Its great to get help like this from forum members, long may we all continue. Love you all, Sam.

11th Jun 2017, 5:38 pm	#22
Top Cap Octode Join Date: Mar 2006 Location: Watford, Hertfordshire, UK. Posts: 1,270	Re: Monster Marshall amp problems. Help!!! Well done Sam, yes I have had only one of these come my way, hope I don't get a second though with mine the fault was pretty obvious Les __________________ Whether the Top Cap is Grid or Anode - touching it will give you a buzz either way!

11th Jun 2017, 6:09 pm	#23
dryjoint Tetrode Join Date: Nov 2009 Location: Southend-on-Sea, Essex, UK. Posts: 60	Re: Monster Marshall amp problems. Help!!! Hi Sam, yup WELL DONE! Always a bit difficult diagnosing faults "at a distance", but it's good to get it sorted and out of the way. Wonder why that speaker was disconnected though....anyway job done and that's what counts. At least you don't have the pain in the proverbial getting new TDAs for it. Enjoy your cruising!

11th Jun 2017, 7:34 pm	#24
Station X Moderator Join Date: Jan 2003 Location: Ipswich, Suffolk, IP4, UK. Posts: 21,288	Re: Monster Marshall amp problems. Help!!! Well done Sam. You met the deadline. Enjoy your boating. __________________ Graham. Forum Moderator Reach for your meter before you reach for your soldering iron.

11th Jun 2017, 7:54 pm	#25
Boater Sam Banned Join Date: Dec 2013 Location: Middlewich, Cheshire, UK. & Winter in the Philippines. Posts: 3,897	Re: Monster Marshall amp problems. Help!!! The speaker cables exit the speaker part of the cabinet via 2 holes below and behind the amp which is on a shelf on top, and plug into the amp with 2 jacks. Unbelievably there are no strain reliefs on the cables! So the lead had been pulled up until the spade connectors came off the speaker. I tied a knot in both inside the speaker box, it won't happen again. It didn't seem to do the amp any harm losing a speaker though. Just happy that the help I got from folk here solved the problem, I really haven't the space or time for these monoliths. It was only a freeby favour anyway. Sam.

11th Jun 2017, 11:35 pm	#26
Refugee Dekatron Join Date: Apr 2012 Location: Worksop, Nottinghamshire, UK. Posts: 5,553	Re: Monster Marshall amp problems. Help!!! Well done. It sounds like that sort of stuff has gone the same way as everything else we find these days.

12th Jun 2017, 8:37 am	#27
Boater Sam Banned Join Date: Dec 2013 Location: Middlewich, Cheshire, UK. & Winter in the Philippines. Posts: 3,897	Re: Monster Marshall amp problems. Help!!! If by gone the same way you mean digital and difficult to work on, you are right. There is very little ordinary electronics in this amp, most of the sound processing is DIL chips, the amps themselves are monolithic chips, and the ECC83 is a preamp token to "the valve sound". All in I consider it to be an advertising farce as it is as removed from a valve amp as it could be, oh, apart from the one. The front panel has a plethora of knobs to make the sound louder and/or even more distorted, lots of push buttons too. A Vox AC30 was a real amp. Sam.

12th Jun 2017, 12:35 pm	#28
Herald1360 Dekatron Join Date: Feb 2007 Location: Leominster, Herefordshire, UK. Posts: 16,535	Re: Monster Marshall amp problems. Help!!! The Marshall is more of an audio processor than just an amplifier with its own particular distortion characteristics. IF it were well engineered, well made and decent service info were available then it would be perfectly fit for purpose, but that IF is a big one nowadays, unfortunately __________________ ....__________ ....\|____\|\|__\|__\_____ .=.\| _---\__\|__\|_---_\|. .........O..Chris....O

12th Jun 2017, 8:01 pm	#29
Boater Sam Banned Join Date: Dec 2013 Location: Middlewich, Cheshire, UK. & Winter in the Philippines. Posts: 3,897	Re: Monster Marshall amp problems. Help!!! Just a little aside to round things off. The ECC83 preamp valve, triodes in cascode, still can't understand why other than it enabled the magic word " VALVE" to be on the front. On inspection, surprise! its a Russian valve! And it looks original too. Curiouser and curiouser. Sam.