Took a while to sort this one but it turned out to be a fairly common problem with amps. Watch as I diagnose and repair from start to finish in real time.
Bought an old Marshall JCM 900 SL-X and all was fine untill i decided to jump the send and return, 'cos i read that the amp that way sounded better... and then when i pulled the patch cable, the amp played like for more 1 minute and then no sound, i had watched your video previously when i searched for Marshall JCM 900 , cleaned the jacks with contact cleaner, and he's back on track! Thank's a lot for your video!
I've the jcm 900 head amp brought to me with same fault.. changed the send jack and signal came back to normal. I did notice someting and that is, from the phase spliter tube just in front of the 47nf 600v caps the circuit dig shows 1k5 going to pin 5 control grid thats fine, but look again it shows two 1k5s going to pin 5 and a wire link feeding the next set of pin 5s.. so I've given each pin 5 it's own 1k5.
These amps are quite good since they are still build in the UK. My recomendation is that once in a while you should clean all of the pots and contacts with Deoxit or other electronic grade cleaner including the valve sockets.
I don’t know how being “still made in the U.K.” makes anything quite good or quite bad. Because in my opinion PCB mounted pots and jacks are shite. No matter where it’s made.
@@TheAxe4Ever I understand your comment but when you have more than 30 years of experience as an electronics engineer you can tell the difference between the different manufacturers and where they source their components. But you are right good and bad products can come out of any factory in any country. Also please note that my opinion is a reflection of my experience.
@@cloudconnect exact inverse for me. Check out the versus vidéo of johan sergeborn.. the DR gets the softer warmer tone surprisingly. That's the one i prefer. (for the A channel, the B is useless.)
@@cloudconnect i have a 5881/6L6 version, when you crank the amp and run a boost or an overdrive pedal with it it sounds really nice but on its own it doesn't sound as good.
Hi Lou thanks for watching. No particular reason, I've never really thought about it. I'm experimenting now with isopropyl alcohol and a hypodermic syringe.
Thank you for the very detailed and informative video. Could you just use a patch cable between SEND and RETURN sockets to diagnose this problem? This could save from taking out PCBs in some cases (of course not much difference if you DO NEED to replace the socket!)
Yes that would definitely diagnose it but only assuming you have that problem in your sights already. Sometimes you don;t and can go off on a different track before circling back to this.
Hi Charles. Why do you say I'm running it without a load? I'm pretty sure the speaker is connected throughout this video. Btw the thing to avoid is no load then HUGE input signal (e.g. crashing chord) but even then it's a really tiny chance of doing any damage to the output transformer.
I have a question for ya... My 98 JCM 900 4100 5881 6L6 makes a small popping or crackle sound only when I turn off the power switch after letting it sit for a couple minutes on stand by? do you know what causes this? other that the amp sounds great!
Sicuramente le valvole finali sono da sostituire, controlla tutti i condensatori elettrolitici. Per il fusibile che salta cosa intendi? Il fusibile di alimentazione 220volt , o uno dei fusibili del finale? Ossia dove si inserisce il plug-in d'uscita? Potrebbero essere bruciate le resistenze sull'uscita da 1/4 di watt, ora non ricordo bene il valore. In rete si può procurare facilmente lo schema elettrico con su scritto il valore delle resistenze in questione, sempre che siano bruciate ovvio.
"This is a strange amplifier. It's a mix of valve and semiconductor." And so have raged a million hot headed arguments on internet forums for decades over that exact observation. hahahha!
I had my 900 re-tubed last summer 2020. It was great all year. Now the sound has dropped out. Sounds like a 20 watt amp. The treble and gain pots were very scratchy. Idk what the issue is. Dirty pots or output Jack's? Lmk. Sending it out for professional help.
@@stuartukguitarampguy5830 I need to, try that because I noticed my 50w 900 doesn't sound as loud. My son has a 40w Badcat that's way louder than my Marshall, I also habe 100w JCM 2000 and that thing is LOUD! I run an "attenuator" through the effects loop so I can crank the amp yet still play in my garage at a decent level. Canni spray deoxit in the Jack's and plug and unplug to kinda clean them?
My 900 50w has lost volume, I was actually thinking I, might need to retube it but I'm reading where a couple of people are saying they had a similar issue and just cleaned the input Jack's or effects loop
Never just spray electrical contact cleaner and turn the amp on while the board is still wet. In another video this dude was also hovering over a live board with 500 volts running through it. You can watch the videos, but if you do what this guy does you might die. I’m not kidding.
Hi Pedro Great question to which I don';t know the exact answer. Certainly mechanical movement of a component causes this (inpput jacks being a typical victim). Maybe the rest is due to repeated heat/cold cycles. Not really sure!
@@stuartukguitarampguy5830 by any chance do you have a schematic of an Orange Matamp OR100 or ORST. I found some online but would like to see if there are different versions...
@@pedrolourenco2707 I have the ORST which I probably also got from the Internet at some point. There's an end screen on all my videos and my email address is there you can contact me that way and I will send it.
Listening to an Englishman wondering why an English amp company made a circuit a weird way is somehow cathartic. Because the English are world renowned for both their electronics and their cuisine..... ( insert Lucas Electric joke here) :)
@@stuartukguitarampguy5830 Did you know that in Heaven the British do the policing, the Germans do the engineering and the Italians do the cooking? But in Hell, the Germans do the policing, the Italians do the engineering, and the British do the cooking? ;) :)
I never bother with switch cleaner. Those sockets are only a quid each. Change them, don't waste your time with switch cleaner. Total waste of time in my experience. It's a short term fix as best.
Ok... but I've always had 100% success using DeOxit - never once had one come back with the same issue.. Also there are so many different types of jack socket it's hard to stock them all. Not to mention on many ampos you have to take the main board out just to change a socket. Customers not amused by £50 bill just for a dirty jack socket!
Horses for causes I guess Stuart. I did buy some DeOxit and wasn't as impressed as everyone seems to be. I got the usual effect of it working short term. Same with pots, I've found the only reliable fix it to just replace them for what they cost. As for taking the boards out, for sure it can be a bit of a pain, but I do it all day long and it's no big deal. I'd much rather remove a board and replace a component than tack a new component on top of an old one. Unfortunately I see that an awful lot and it makes the hair on my neck stand up lol I've seen resistors soldered on top of resistors that were breaking down, then you get an intermittent half value situation and it throws that part of the circuit out of whack. I guess we all have our own way of doing things and maybe I'm being a bit OCD, but if a customer opens an amp I've repaired, I don't want them to be able to see what's been done. Good channel, I've enjoyed looking through your video ☺️
Agreed. Most of the time they are sprung because of cheaper metal. Another thing that happens is that the sprung portion actually moves within the plastic casing, away from the stationary contact. This can happen to even a new part upon installation.
@@DrWatts-bi1jv These jacks are notorious for going bad, once the outer layer is broken they oxidize, no matter how often you clean them they will keep oxidizing, changing them is cheaper and faster, there's no real reason not to change them. They can build up so much resistance that they practically shut off!
naprawianie wszystkiego sprayem do kontaktu, żenada . Dziadek popsyka i zadowolony zgoli gościa na ładnych parę funciaków, zamiast gniazdo wylutować, porządnie wyczyścić i sprawdzić jak należy pod kontem zimnych lutów których w takich wzmacniaczach jest od liku
Little by little I'm going through all of your videos - I'm stunned with every one ! Excellent work - thank you !
Thanks Dirk
Bought an old Marshall JCM 900 SL-X and all was fine untill i decided to jump the send and return, 'cos i read that the amp that way sounded better... and then when i pulled the patch cable, the amp played like for more 1 minute and then no sound, i had watched your video previously when i searched for Marshall JCM 900 , cleaned the jacks with contact cleaner, and he's back on track!
Thank's a lot for your video!
NIce one, well done.
I'm loving the lack of moulded plugs in your extension lead in the background of the video! Proper old school!
Ha ha. Yeah!
This is exactly what I've done to clean the send and return contacts. It worked for me!
Excellent well done!
Nice fix, and exploration of the initial fault..Good job..Ed..Herts..uk..😀
Thanks Ed.
I've the jcm 900 head amp brought to me with same fault.. changed the send jack and signal came back to normal. I did notice someting and that is, from the phase spliter tube just in front of the 47nf 600v caps the circuit dig shows 1k5 going to pin 5 control grid thats fine, but look again it shows two 1k5s going to pin 5 and a wire link feeding the next set of pin 5s.. so I've given each pin 5 it's own 1k5.
Hi Wayne Interesting, yes definitely better to have separate 1K5. I wonder why they linked them like that?
Stuart
On my JCM900, similar issue. I ended up just using a short length of pedal cable and connecting it between send and return.
YEs that's a get out of jail trick!
These amps are quite good since they are still build in the UK. My recomendation is that once in a while you should clean all of the pots and contacts with Deoxit or other electronic grade cleaner including the valve sockets.
I don’t know how being “still made in the U.K.” makes anything quite good or quite bad. Because in my opinion PCB mounted pots and jacks are shite. No matter where it’s made.
@@TheAxe4Ever I understand your comment but when you have more than 30 years of experience as an electronics engineer you can tell the difference between the different manufacturers and where they source their components. But you are right good and bad products can come out of any factory in any country. Also please note that my opinion is a reflection of my experience.
The dual reverb is easily the worst 900. SL-X is the king, followed by the mkiii.
@@cloudconnect exact inverse for me. Check out the versus vidéo of johan sergeborn.. the DR gets the softer warmer tone surprisingly. That's the one i prefer. (for the A channel, the B is useless.)
@@cloudconnect i have a 5881/6L6 version, when you crank the amp and run a boost or an overdrive pedal with it it sounds really nice but on its own it doesn't sound as good.
New sub from Quebec , love your channel ! Is there a reason you don't secure the surrounding area with Scott Towel when shooting De-Oxit ?
Hi Lou thanks for watching. No particular reason, I've never really thought about it. I'm experimenting now with isopropyl alcohol and a hypodermic syringe.
Thank you for the very detailed and informative video. Could you just use a patch cable between SEND and RETURN sockets to diagnose this problem? This could save from taking out PCBs in some cases (of course not much difference if you DO NEED to replace the socket!)
Yes that would definitely diagnose it but only assuming you have that problem in your sights already. Sometimes you don;t and can go off on a different track before circling back to this.
That de soldering gun is nice...
Yes crazy cheap too. Under £100!
I get a little nervous when you run the amp with no load, but I assume you know what you're doing. Good fix!
Hi Charles. Why do you say I'm running it without a load? I'm pretty sure the speaker is connected throughout this video.
Btw the thing to avoid is no load then HUGE input signal (e.g. crashing chord) but even then it's a really tiny chance of doing any damage to the output transformer.
Towards the end of the video, yes. But a few seconds with no load won't hurt anything at all even with an input signal.
@@cloudconnect In fact ANY amount of time with no load is fine, as long as there isn't an input signal. Best to have one connected though.
I'd love one of those desoldering tools
They're REALLY cheap! About $100 from memory. Let me know if you need the details.
I have a question for ya... My 98 JCM 900 4100 5881 6L6 makes a small popping or crackle sound only when I turn off the power switch after letting it sit for a couple minutes on stand by? do you know what causes this? other that the amp sounds great!
Hi. No, sorry not sure what that might be. If its not causing an issue maybe leave well enough alone?
Quick question I am going to build a guitar amp does the anode impedance of the output tube change if using cathode bias to grid bias.
Hi That's above my pay grade I'm afarid! Good luck with the build.
My jcm 900 low bass very small cant reach..u have solution
My JCM 900 Dual Reverb 100 watt head had the sound start going lower and then lost sound and the fuse keeps blowing?
Sicuramente le valvole finali sono da sostituire, controlla tutti i condensatori elettrolitici. Per il fusibile che salta cosa intendi? Il fusibile di alimentazione 220volt , o uno dei fusibili del finale? Ossia dove si inserisce il plug-in d'uscita? Potrebbero essere bruciate le resistenze sull'uscita da 1/4 di watt, ora non ricordo bene il valore. In rete si può procurare facilmente lo schema elettrico con su scritto il valore delle resistenze in questione, sempre che siano bruciate ovvio.
"This is a strange amplifier. It's a mix of valve and semiconductor." And so have raged a million hot headed arguments on internet forums for decades over that exact observation. hahahha!
I'm not getting involved.... :)
@@stuartukguitarampguy5830That could very well be what the Dual Reverb engineer at Marshall said when he was asked to design a new all tube amp. ha. 🙂
That happens on my laney gc50. Totally cuts out the sound. Then I just plug in a patch cable between send and return and it works just fine :)
Hi Daniel A squirt of cleaner and work the jack plug in and out a few times and that should sort it!
@@stuartukguitarampguy5830 sure but having a patch cable handy just in case can save be a life saver in a gig situation.
I had my 900 re-tubed last summer 2020. It was great all year. Now the sound has dropped out. Sounds like a 20 watt amp. The treble and gain pots were very scratchy. Idk what the issue is. Dirty pots or output Jack's? Lmk. Sending it out for professional help.
If it has FX send and return jacks you could try cleaning those by plugging a jack plug in and out a few times. Bit of a long shot though.
@@stuartukguitarampguy5830 I need to, try that because I noticed my 50w 900 doesn't sound as loud. My son has a 40w Badcat that's way louder than my Marshall, I also habe 100w JCM 2000 and that thing is LOUD! I run an "attenuator" through the effects loop so I can crank the amp yet still play in my garage at a decent level. Canni spray deoxit in the Jack's and plug and unplug to kinda clean them?
My 900 50w has lost volume, I was actually thinking I, might need to retube it but I'm reading where a couple of people are saying they had a similar issue and just cleaned the input Jack's or effects loop
I had to replace the output transformer.
What year was this amp built?
Not sure I'm afraid.
Is deoxid conductive !
No, I don't believe so!
Never just spray electrical contact cleaner and turn the amp on while the board is still wet. In another video this dude was also hovering over a live board with 500 volts running through it. You can watch the videos, but if you do what this guy does you might die. I’m not kidding.
Yup or you could jump a small cord from input to output and save repair cost
Why do dry joints happen? Exposure to cold?
Hi Pedro Great question to which I don';t know the exact answer. Certainly mechanical movement of a component causes this (inpput jacks being a typical victim). Maybe the rest is due to repeated heat/cold cycles. Not really sure!
@@stuartukguitarampguy5830 repeated heat/cold cycle makes sense. Would the joint material make any diference. Do they use 60/40 solder?
@@pedrolourenco2707 Again I am unsure tbh.
@@stuartukguitarampguy5830 by any chance do you have a schematic of an Orange Matamp OR100 or ORST. I found some online but would like to see if there are different versions...
@@pedrolourenco2707 I have the ORST which I probably also got from the Internet at some point. There's an end screen on all my videos and my email address is there you can contact me that way and I will send it.
Cool😂
I wish you lived closer to me I have some things I would like to give you.
If it's gold bars, I'm sure I could arrange a courier collection....
Listening to an Englishman wondering why an English amp company made a circuit a weird way is somehow cathartic. Because the English are world renowned for both their electronics and their cuisine..... ( insert Lucas Electric joke here) :)
What's wrong with beans on toast and fish 'n' chips???
@@stuartukguitarampguy5830 Did you know that in Heaven the British do the policing, the Germans do the engineering and the Italians do the cooking? But in Hell, the Germans do the policing, the Italians do the engineering, and the British do the cooking? ;) :)
@@tjsogmc Very good!
@@tjsogmc best Joke I heard in a while!🤣👍
PCB mounted pots and jacks. Ugh!
You're being kind. I'd stretch to 'double ugh'...
Before i watch this video i can tell you its prob Dirty EFX loop got many a good amp cheap bc of this
Ha ha. Yes it's my favourite fix too!
I never bother with switch cleaner. Those sockets are only a quid each.
Change them, don't waste your time with switch cleaner.
Total waste of time in my experience.
It's a short term fix as best.
Ok... but I've always had 100% success using DeOxit - never once had one come back with the same issue.. Also there are so many different types of jack socket it's hard to stock them all. Not to mention on many ampos you have to take the main board out just to change a socket. Customers not amused by £50 bill just for a dirty jack socket!
Horses for causes I guess Stuart.
I did buy some DeOxit and wasn't as impressed as everyone seems to be. I got the usual effect of it working short term. Same with pots, I've found the only reliable fix it to just replace them for what they cost.
As for taking the boards out, for sure it can be a bit of a pain, but I do it all day long and it's no big deal. I'd much rather remove a board and replace a component than tack a new component on top of an old one. Unfortunately I see that an awful lot and it makes the hair on my neck stand up lol
I've seen resistors soldered on top of resistors that were breaking down, then you get an intermittent half value situation and it throws that part of the circuit out of whack.
I guess we all have our own way of doing things and maybe I'm being a bit OCD, but if a customer opens an amp I've repaired, I don't want them to be able to see what's been done.
Good channel, I've enjoyed looking through your video ☺️
Agreed. Most of the time they are sprung because of cheaper metal. Another thing that happens is that the sprung portion actually moves within the plastic casing, away from the stationary contact. This can happen to even a new part upon installation.
@@DrWatts-bi1jv These jacks are notorious for going bad, once the outer layer is broken they oxidize, no matter how often you clean them they will keep oxidizing, changing them is cheaper and faster, there's no real reason not to change them. They can build up so much resistance that they practically shut off!
The best way to fix the jcm 900 is to just throw it in the dumpster
Ooo, harsh!
naprawianie wszystkiego sprayem do kontaktu, żenada . Dziadek popsyka i zadowolony zgoli gościa na ładnych parę funciaków, zamiast gniazdo wylutować, porządnie wyczyścić i sprawdzić jak należy pod kontem zimnych lutów których w takich wzmacniaczach jest od liku
Good evening can i get your email? To send picture of my svt pro-7 and where to order the parts that i need,thank you and more power to your channel🙏
Hi At the end of every video there is a splash screen. My email is on there. Tx.