Every SMT component amp chassis is a foundation for a point to point all tube circuit. Install a power amp resistor on the output jack to prevent a no load scenario. Great work sir!! You made this amp alive again!! :)
Had the same with an Orange OR200 amp. Worked fine up to half power then major distortion. Replaced output tranformer at a huge cost but it is a 200w amp and no problems.
To remove the FET's without damaging the pads, just clip the leads off and then de-solder each lead and pull it out. It'll save you de-laminating the through hole pads and possibly damaging the barrel. By the way, I learn much from your channel, thanks!
I wish as I had read this comment before I fixed my Bugera G5, which is probably based on this amp. Yeah, mistakes were made, things were learned. Now the MOSFETs are wired and mounted on heatsinks at the upper side (where the tubes are). The board is a bit messed up, I didn't want to risk messing that area again
@@DennisCameronMusic Sometimes it helps if you instead of sucking solder away just add solder first to every pad, then it can be possible to enough heat them all at the same time and pull the component out. Sometimes those holes really are very small and tight and the leads can get very much stuck in them.
Stuart, It's always exciting to see new content from you. I think the fact that you show the process you use and explain the issues simply is why so many people watch you. I know I've learned a lot watching your channel. This was interesting, but I don't know if I would have clipped a new transformer like you did. However, I'm a novice and voltages scare me. Always informative and entertaining. Thanks, Mike
Hi Mike Yes super dangerous what I did, but of course I was very careful and checked all connections wer ok before switching on. Not for the faint hearted!
Funnily enough I diagnosed the exact same problem in my HT5R Combo last week. I'm not paying £75 for their crappy OT though! The Hammond 125B is a direct replacement if I'm not mistaken.
Pretty peculiar little amp, because if I have understood correctly, the triodes of that 12BH7 work as a push pull output stage. Those around 450V plate voltages seem quite high but those tubes have been widely used as oscilloscope deflection tubes at those voltages, and often been tortured at max plate dissipation as well. Possible no load situation could have killed that OT. Very nice that you could fix it. 👍 The output power of that high voltage beast could be even 3-4 watts, I guess. 😂 That kind of output stage could make quite a nice reverb driver when using 8 ohm reverb tank.
Yes I was surprised at that HT. Yes it's a standard push-pull arrangement but they drive the cathodes via those FETS for some reason. I think this died due to being thrashed solid for 2 hours on max volume. Crazy. Not a gigging amp at all!
@@stuartukguitarampguy5830 Thanks, because I was already wondering the purpose of those FETs. Whether no load or output stage driven to clipping, voltage spikes in both cases, and OT does not like either option at all. And no wonder if those fets are prone to failing as well. 😁
Poke holes in the solderwick with an awl or tiny jeweler's screwdriver and then you can place the wick directly over the stub of each component lead. Adding the special low-temperature solder known as ChipQuick is also helpful; it stays liquid for almost 10 seconds without further heat being applied (ChipQuick is also very helpful for removing SMD parts with multiple pins). PS, I'd recommend adding heatsinks to those Mosfets; the discoloration of the board indicates that both the mosfets and the resistors are generating heat. Unfortunately you can't heatsink the resistors, nor easily fit larger ones, but replacements could be mounted a little above the board for better air flow.....
Good tips thanks. Particularly you have reminded me to get some low melt solder. There's an excellent RUclips site caleled Northridge Fix if you haven;t seen it. Amazing work on smd boards.
Excellent diagnosis and repair Stuart.. About five years ago I had the same thing happen to my FBJ .. All the readings on the output TX looked okay.. But I had another TX kicking around so I thought there's nothing to loose and I connected it up. Hey presto it worked perfectly. I still have the faulty TX but can't figure out to this day what's actually wrong with it, but there's something going on for sure. I'm pleased to say I'm one of your 'million' as I've been with you from the start of your YT channel. Congratulations and well deserved.
@@pda49184 test it with a megger and the truth will be revealed. Many times you check something with a VOM and it's fine, but the component fails under load. The VOM only puts out a few milliamps, not enough to find some problems.
Good tip about marking the bad part. Even though I've never once ever took a bad part off then put it back on thinking it was the new part causing me hours more diagnostic time, I mark the old part with a paint marker pen- red for bad and yellow for maybe still good.
@@stuartukguitarampguy5830 I also put a yellow dot on valves that are weak but still useful for testing or something. Otherwise I would have to throw it away which is wasteful, or mistakenly think that it's good a year or two later when I take it from the spares box. The chips you replace on this amp I would either chuck them in the bin because they're not rare or expensive, or I would mark them with a white dot and put them in the spares. White or green I know that it's a good used part (I still would test it before installing)
I actually have one but yes, they don;t supply them. Can;t have other engineers stealing those top secret ideas like using op amps and FETs 'n' stuff, can we???
@@brivington2011 I worked for a manufacturer that scrupulously guarded their designs like it was a covert CIA operation. I guess they didn't want the competition to know that the machine hydraulics were straight out of the Bosch -Rexroth handbook available to the public.
I got a HT5210 (2x10inch speakers) combo a few years ago and a few days ago I wanted to play and found that the Overdrive channel has No gain anymore and it just sound clean, even when I crank the gain and volume. And when I switch to the Clean channel, I get a very low volume, still clean. It still the same when I plug in headphones on the emulated output. I tried pluging/unpluging every cables several times, playing through the FX loop(which I usually do) or directly in the main input through a single cable. Still the same. Any idea if it's the preamp valve or perhaps the power valve? I should be able to replace the preamp valve if its the problem but im not that tech savy with amps so I wouldnt be comfortable with the power one since you got to bias it(or something ?). I usually play at pretty low volume with a pedal board and really rarely ever cranked it. Any help would be greatly appreciated since money is tight lately and well, this is quite a rare amp(the 2x10 model) Thx
Dear Mr Spell - or may I called you Darkened? It's unlikely to be the valve BUT this is such a simple check it may be worth doing. The preamo is an ECC83 and the power is a 12BH7. Don't worry about bias. If that doesn;t fix it the next likely is the two power FETs. It could also be the output transformer like on my one. I expect you'll need a tech to look at it if the valve swap doesn't do anything.
Brad's guitar garage has been working on a replacement DSL board for those ones where the board itself goes conductive but I think (a) it's the 100 watt version and (b) he's maybe just at the prototype stage and hasn't fully populated one and installed into an amp yet but check him out
@@stuartukguitarampguy5830 Using two POWER FETS as a phase splitter/phase inverter is very unusual for guitar amplifiers. I think maybe Music Man amplifiers from the late 70's used also a Solid Stage Phase Inverter/Phase Splitter also but I'm not sure. Its Rare to see amplifiers using a Solid State Phase Inverter plus only using ONE output tube in a push pull mode which is also very unusual.
Consumer electronics mentality. They knew when they made these that they were destined for the landfill in 10 years or so but hey, you can't sell as many new amps if your old ones last too long and are readily available on the used market. People love to bash Mesa for lack of repairability, but smt components are the mark of a true sociopath imo.
At 11:25, the whopping 462 volts B+ measured at the 12BH7 was probably a clue, because it appears the tube is idling at virtually no current, which indicates an incorrect load, due in this case to the bad output transformer. It would have been instructive to measure the B+ after the transformer was replaced; I would bet that it dropped by at least 20 or 30 volts. As for the blown output transformer, your megger might have shown internal leakage or capacitive coupling. PS, 75 pounds for a puny transformer like this is highway robbery! You could probably have looked at a tube manual and figured out an appropriate impedance match so that you could replace the original transformer with a Hammond or something else for half that price, or measure the turns ratio of the brand new transformer before installation so that you can find a more reasonably priced substitute if you ever need to replace one again. You'd be doing a service for other Blackstar owners and their long-suffering technicians!
Yes I thought that BUT those power resistors in the FET path were getting warm and drawing current, so I assumed thart must be going through the primary? Yes outrageous! It's super rare to replace one though, so I probably won;t seek out an alternative.
For that price, it should have been a Heyboer or Mercury Magnetics, instead of some cheap Chinese thing! I suggested to Stewart in another comment that he probably should have measured the turns ratio of the replacement transformer and included that info in the video so that other technicians would know what to use as a replacement in future. The blazingly high 463 V at the plates of the 12BH7 output tube might have been a clue that the tube was drawing virtually no current due to a wacky transformer load. I bet the B+ dropped by at least 20 to 30 volts when a new transformer was installed.
@@gingercat777 I would have gotten a similarly speced OT from eBay before I would spend that much on a Blackstar brand component. It's not like Blackstar makes those OTs anyway- they get them from some supplier in China, probably the same one selling them on eBay for $20.
Oh god...your bill will cost more than the amp! I have an ht studio20 head under my bed. It's under my bed because I would give it away, but I think anyone I give it to will experience crushing disappointment.
I've watched a few videos where they add a bit of fresh solder before using the braid to ease component removal. Not at all telling you how to do your business sir.
Every SMT component amp chassis is a foundation for a point to point all tube circuit. Install a power amp resistor on the output jack to prevent a no load scenario. Great work sir!! You made this amp alive again!! :)
Thanks. Hmmm I feel a 120 tube project coming on...
Had the same with an Orange OR200 amp. Worked fine up to half power then major distortion. Replaced output tranformer at a huge cost but it is a 200w amp and no problems.
Thanks Stewart.
To remove the FET's without damaging the pads, just clip the leads off and then de-solder each lead and pull it out. It'll save you de-laminating the through hole pads and possibly damaging the barrel. By the way, I learn much from your channel, thanks!
I wish as I had read this comment before I fixed my Bugera G5, which is probably based on this amp.
Yeah, mistakes were made, things were learned. Now the MOSFETs are wired and mounted on heatsinks at the upper side (where the tubes are). The board is a bit messed up, I didn't want to risk messing that area again
Hi Dennis Ah yes, of course I know that trick but had somehow forgotten it this time!
@@stuartukguitarampguy5830 I'm sure you've forgotten more than most of us will ever know.
@@tjsogmc Ha ha! I expect you too have an area of expertise about which I know zippo!
@@DennisCameronMusic Sometimes it helps if you instead of sucking solder away just add solder first to every pad, then it can be possible to enough heat them all at the same time and pull the component out. Sometimes those holes really are very small and tight and the leads can get very much stuck in them.
Stuart,
It's always exciting to see new content from you. I think the fact that you show the process you use and explain the issues simply is why so many people watch you.
I know I've learned a lot watching your channel.
This was interesting, but I don't know if I would have clipped a new transformer like you did. However, I'm a novice and voltages scare me.
Always informative and entertaining.
Thanks,
Mike
Hi Mike Yes super dangerous what I did, but of course I was very careful and checked all connections wer ok before switching on. Not for the faint hearted!
Funnily enough I diagnosed the exact same problem in my HT5R Combo last week. I'm not paying £75 for their crappy OT though! The Hammond 125B is a direct replacement if I'm not mistaken.
That's very useful thanks. I'll make a note of it for next time.
Pretty peculiar little amp, because if I have understood correctly, the triodes of that 12BH7 work as a push pull output stage. Those around 450V plate voltages seem quite high but those tubes have been widely used as oscilloscope deflection tubes at those voltages, and often been tortured at max plate dissipation as well.
Possible no load situation could have killed that OT.
Very nice that you could fix it. 👍
The output power of that high voltage beast could be even 3-4 watts, I guess. 😂
That kind of output stage could make quite a nice reverb driver when using 8 ohm reverb tank.
Yes I was surprised at that HT. Yes it's a standard push-pull arrangement but they drive the cathodes via those FETS for some reason. I think this died due to being thrashed solid for 2 hours on max volume. Crazy. Not a gigging amp at all!
@@stuartukguitarampguy5830 Thanks, because I was already wondering the purpose of those FETs. Whether no load or output stage driven to clipping, voltage spikes in both cases, and OT does not like either option at all. And no wonder if those fets are prone to failing as well. 😁
Poke holes in the solderwick with an awl or tiny jeweler's screwdriver and then you can place the wick directly over the stub of each component lead. Adding the special low-temperature solder known as ChipQuick is also helpful; it stays liquid for almost 10 seconds without further heat being applied (ChipQuick is also very helpful for removing SMD parts with multiple pins).
PS, I'd recommend adding heatsinks to those Mosfets; the discoloration of the board indicates that both the mosfets and the resistors are generating heat. Unfortunately you can't heatsink the resistors, nor easily fit larger ones, but replacements could be mounted a little above the board for better air flow.....
Good tips thanks. Particularly you have reminded me to get some low melt solder. There's an excellent RUclips site caleled Northridge Fix if you haven;t seen it. Amazing work on smd boards.
Excellent diagnosis and repair Stuart.. About five years ago I had the same thing happen to my FBJ .. All the readings on the output TX looked okay.. But I had another TX kicking around so I thought there's nothing to loose and I connected it up. Hey presto it worked perfectly. I still have the faulty TX but can't figure out to this day what's actually wrong with it, but there's something going on for sure. I'm pleased to say I'm one of your 'million' as I've been with you from the start of your YT channel. Congratulations and well deserved.
Thanks! Yes I wonder if it just breaks down under high voltage?
@@stuartukguitarampguy5830 , It would have been interesting to see if your megger could find a leakage fault.
@@pda49184 test it with a megger and the truth will be revealed. Many times you check something with a VOM and it's fine, but the component fails under load. The VOM only puts out a few milliamps, not enough to find some problems.
More good work Stuart.
Thanks Denni
As always, your videos are very helpful and encouraging!
Thanks Tommy
I'm still planning to drop off my jcm900 to you, keep watching your videos and founding them very interesting. Thank you
Ok great.
Good tip about marking the bad part. Even though I've never once ever took a bad part off then put it back on thinking it was the new part causing me hours more diagnostic time, I mark the old part with a paint marker pen- red for bad and yellow for maybe still good.
Yes good plan!
@@stuartukguitarampguy5830 I also put a yellow dot on valves that are weak but still useful for testing or something. Otherwise I would have to throw it away which is wasteful, or mistakenly think that it's good a year or two later when I take it from the spares box.
The chips you replace on this amp I would either chuck them in the bin because they're not rare or expensive, or I would mark them with a white dot and put them in the spares. White or green I know that it's a good used part (I still would test it before installing)
Well done Stuart, same with me I don't like surface mount . Great result
It's super hard to work on. Have a look at a RUclips channel called Northridge Fix, really interesting!
Just had a Blues Junior doing the same . I also didn't at first think it would be the OT transformer .
Yes I rarely suspect the OT as they don;t often go. Just had another one today though on a Marshall!
Quite a poser, this little unit. I'm impressed by your perseverance in deducing the issue. Enjoy your weekend, Stuart. Cheers!
Thanks Alex.
I really enjoy watching your videos - Thank you !!
Nice work Stuart...Bit of a pig those Blackstar amps..😮..😅..Ed..uk
Thanks Edward, always good to hear from you.
Great job! I’ve heard that Blackstar does not provide schematics, is that true?
I actually have one but yes, they don;t supply them. Can;t have other engineers stealing those top secret ideas like using op amps and FETs 'n' stuff, can we???
@@brivington2011 I worked for a manufacturer that scrupulously guarded their designs like it was a covert CIA operation. I guess they didn't want the competition to know that the machine hydraulics were straight out of the Bosch -Rexroth handbook available to the public.
I got a HT5210 (2x10inch speakers) combo a few years ago and a few days ago I wanted to play and found that the Overdrive channel has No gain anymore and it just sound clean, even when I crank the gain and volume. And when I switch to the Clean channel, I get a very low volume, still clean. It still the same when I plug in headphones on the emulated output.
I tried pluging/unpluging every cables several times, playing through the FX loop(which I usually do) or directly in the main input through a single cable. Still the same.
Any idea if it's the preamp valve or perhaps the power valve? I should be able to replace the preamp valve if its the problem but im not that tech savy with amps so I wouldnt be comfortable with the power one since you got to bias it(or something ?).
I usually play at pretty low volume with a pedal board and really rarely ever cranked it.
Any help would be greatly appreciated since money is tight lately and well, this is quite a rare amp(the 2x10 model)
Thx
Dear Mr Spell - or may I called you Darkened?
It's unlikely to be the valve BUT this is such a simple check it may be worth doing. The preamo is an ECC83 and the power is a 12BH7. Don't worry about bias. If that doesn;t fix it the next likely is the two power FETs. It could also be the output transformer like on my one. I expect you'll need a tech to look at it if the valve swap doesn't do anything.
Marshall doesn't have boards for a dsl 40 c anymore . Unless u may know where I can get one I'm out of luck .
Brad's guitar garage has been working on a replacement DSL board for those ones where the board itself goes conductive but I think (a) it's the 100 watt version and (b) he's maybe just at the prototype stage and hasn't fully populated one and installed into an amp yet but check him out
@@Swodie_Jeetin Thx for the response , I'll çk wíth brad n see if he has any ideas . Have a good day .
Those FETS that you replaced do what to the phase splitter section?
My best understanding is that the 12BH7 is in push-pull mode but is being driven by 2 power FETS in the cathodes which act as a phase-splitter.
@@stuartukguitarampguy5830 Using two POWER FETS as a phase splitter/phase inverter is very unusual for guitar amplifiers. I think maybe Music Man amplifiers from the late 70's used also a Solid Stage Phase Inverter/Phase Splitter also but I'm not sure. Its Rare to see amplifiers using a Solid State Phase Inverter plus only using ONE output tube in a push pull mode which is also very unusual.
@@waynegram8907 Ah but don;t forget the 12BH7 is two tubes in one envelope. Like the ECC83 but more powerful. So it's standard push-pull.
Consumer electronics mentality. They knew when they made these that they were destined for the landfill in 10 years or so but hey, you can't sell as many new amps if your old ones last too long and are readily available on the used market. People love to bash Mesa for lack of repairability, but smt components are the mark of a true sociopath imo.
It's all down to production cost as I'm sure you know.
At 11:25, the whopping 462 volts B+ measured at the 12BH7 was probably a clue, because it appears the tube is idling at virtually no current, which indicates an incorrect load, due in this case to the bad output transformer. It would have been instructive to measure the B+ after the transformer was replaced; I would bet that it dropped by at least 20 or 30 volts. As for the blown output transformer, your megger might have shown internal leakage or capacitive coupling. PS, 75 pounds for a puny transformer like this is highway robbery! You could probably have looked at a tube manual and figured out an appropriate impedance match so that you could replace the original transformer with a Hammond or something else for half that price, or measure the turns ratio of the brand new transformer before installation so that you can find a more reasonably priced substitute if you ever need to replace one again. You'd be doing a service for other Blackstar owners and their long-suffering technicians!
Yes I thought that BUT those power resistors in the FET path were getting warm and drawing current, so I assumed thart must be going through the primary?
Yes outrageous! It's super rare to replace one though, so I probably won;t seek out an alternative.
Actually you only need a gas soldering iron with air or a hot air station they are both very cheap to remove SMT components. Not expensive at all.
Hi Anthony TBH I hardly ever need to take an SMT off so it's not worth it.
Blackstar has a terrible reputation. So many amp techs refuse to service them
Definitely not my favourite. Worst amp I've seen so far is Fender Bassbreaker 15
What a crazy way to build a simple amp and then you get robbed for the OT. 😡
For that price, it should have been a Heyboer or Mercury Magnetics, instead of some cheap Chinese thing! I suggested to Stewart in another comment that he probably should have measured the turns ratio of the replacement transformer and included that info in the video so that other technicians would know what to use as a replacement in future. The blazingly high 463 V at the plates of the 12BH7 output tube might have been a clue that the tube was drawing virtually no current due to a wacky transformer load. I bet the B+ dropped by at least 20 to 30 volts when a new transformer was installed.
@@gingercat777 I would have gotten a similarly speced OT from eBay before I would spend that much on a Blackstar brand component. It's not like Blackstar makes those OTs anyway- they get them from some supplier in China, probably the same one selling them on eBay for $20.
Oh god...your bill will cost more than the amp! I have an ht studio20 head under my bed. It's under my bed because I would give it away, but I think anyone I give it to will experience crushing disappointment.
Hi Johnny YEs these amps are made down to a price and as such they are not easily repairable. Spares and repairs on eBay?
Interesting OT failure.
Yes quite rare. It had been thrashed though.
I've watched a few videos where they add a bit of fresh solder before using the braid to ease component removal. Not at all telling you how to do your business sir.
Hi Dave If you use a good quality resin impregnated braid, you should be ok.
Crikey, it's just an amp. 1968 colour TV's had less components than that thing.
Yes exactly!