Mesa Boogie Studio Caliber .22 Issues & Repair (Part 1)
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- Опубликовано: 26 авг 2024
- This shows some typical issues in these amps. They've had a good run, being about as old as I am, and they can be made reliable, providing they're not too far gone. Here's the first video of this particular beasts restoration. Standby for the coming vids.
Note:
Disregard my comments about the footswitch control circuit polarity.
I was confused with the polarity of the EQ supply on the + models.
I've started work (and research) on my Mesa DC3 this past year and this week got a studio 22+ (w/o the GEQ) that has intermittent red plating. I have been watching videos and going through forums on these amps like crazy and your video has been the most informative source so far. Thank yo uso much for that.
Side note, the regular and plus each came with EQ as a separate option.
I had the same issue with the send return jacks and put a cable in it per Mesa’s recommendation and it corrected the issue.
I am glad I found your vid. My buddy was going to bring is studio 22 over as the EQ wasnt working. I found this last night and saw what you did for this one. I tested the footswitch and front panel switch. I was going to test the voltages entering and exiting the EQ section, but when I looked at the board, I found a charred section like this one. Same resistor, (it looks like it is 560ohm but I can't make out the bands. It tests OL so it is fried. This is the secction that feeds the EQ so I am going to pull the board and fix that resistor. Will check some of the other components, too. Thanks for your great videos...this one was a big help!!
You'll find the schematic readily available online.
While no Mesa Boogie schematics are 100% accurate, it should help you along.
@@BradsGuitarGarage I found one. It was marked on that resistor changing from stock up to 1K 2W. I just put in a new resistor and the amp sounds killer! Both channels working along with the Graphic EQ. The schematic I found is handwritten and really hard to read values, etc. Thanks again for your channel, Brad. Great content.
I cannot seem to add a picture here but the paramount fix of all time addresses the chassis wiring. My amp in comparison is the original 22. Anyways, I personally used short male/female spade links with a color coded scheme to make the circuit board friendly for both removable and servicing. I also used a shielded coax to route the feed from the master pot across the (grounded) buss bar to its termination point at the EQ/DR entry. BTW that was locally grounded on both ends to prevent grounding loops and those parasitic oscillations you already know about.
With respect to that grounded bus bar for the pots, I did add extra grounding points to the circuit board again with M/F spade links. On the plate dropping resistor branch, in particular the 5.6K, I replaced it with a 5W resistor from the KOA Speer MOS family. What is stock in these amps has no power dissipation margin such that one bad EL84 with a grid short will take that resistor out. I know that... because it happened to me. You always get superior products from KOA Speer, as I tip my hat to them. I went on to replace the 10K resistor that feeds the 12AX7s the same way (5W), the foot switch circuits 560 ohms/5W and for the 470 ohm finals screens/3W. A bit big (on times) but you J-lead them.
The OEM standoffs are pretty much garbage and so I used some one inch 6-32 types you can get for a couple of bucks off EBay (China) like my spade M/F links too. You can follow that up with the mating plastic screws along with their washers. In the end, I ended up with an amp I could jack to ten on both preamp and the master without all the squeals. If you want to see what this f..ker can really do, run it into an external sealed back cabinet too.
Nice write up. I like to replace the screens with 1k 5w dale wire wounds. Randall smith hates techs and players alike. That much is clear.
RE spade links to facilitate board removal. Are we talking from the pots & reverb ONLY. What about the HT connections ( using spade links there would seem more problematic). I'm about to try a pull the board - so using spade links is of interest.
Great video mate & many thanks ! I have a 22+ and currently looking at "bias taming" options . Much appreciated.
Wow, thanks a lot for your video. Many years ago I sold my 22+, Now I am an happy owner of a Mark III.. but I tell you what, in an ext cab it reminds me a lot the 22+!!! I would like to compare them, especially the high tones are really, really similar.
Just got a Mk3 on the bench this week.
I currently have my studio 22 (1985) busted open to work on the channel switching. Finding the right vactrols has been a real drag, and Mesa doesn't return calls apparently. I have a schematic, but I can't find a parts list to get actual part numbers on this old gal. Any chance one of you gentlemen have that you could share, and a good resource in the US for the parts?
Excellent video of a breakdown/repair, I am looking forward to part 2!
Hey brad greetings from Detroit Michigan. Next time, try a pair of welders vice grip pliers to seat those turrets. Beats a hammer!
late to this channel & this vid, tantalums dont dry out like electros, but when they fail, they fail short.... imo they're best replaced, a good 105C electro will do just as well.
They are very intolerant of voltage spikes and as such, don't belong in circuits without regulated supplies or in a position to be damaged by a faulty 12ax7 etc etc etc.
Looks like the power tube sockets were cooked somehow on that board. On the other hand, I never saw such a strange way to replace components!
You’re a funny cxxt mate, made me laugh. Good video too.
WOnder why they soldered the power tube sockets right to the circuit board. Not a good idea imho. Pre-amp tubes it's fine, but not Power tubes...Those jokers get hot.
Bought a 22 non plus version. Reverb does not work, any clues on what to check besides the tube? Also, is there a mod to add the “plus”? I believe it’s just the drive master, right?
Mesa love using underrated coupling caps!
That they most certainly do.
With every generation.
It will never end.
To do so would be to admit their mistake.
And abusers never do that.
@@BradsGuitarGarage and it’s fitting that Gibson bought them 😂😂
Both parties will end up with what they deserve.
@@BradsGuitarGarage literally just air toasted you lol
i suspect i can see the problem right here - R131 is conducting THROUGH the carbon on the board.
I had a 1986 studio 22. It was so unreliable and noisy when cranked. It sounded great but I just couldn't trust it. Sold it on and replaced it with a 1995 Delta blues 🙂
Sounds like you need a trusted local tech.
I can let you know who's close by if you drop me an email.
I just bought a Boogie studio series for $300. Not sure if thats a good deal or not but it is tube amp.
Brad I have a 22+ w/o graffiti EQ that intermittently goes into a mode where all three of the tone controls no longer function correctly but actually affect volume when you turn them up and down. Have you run into this condition before?
27 volt zeners +47ohm resistors on the screens will tame the bias😉
I've been meaning to try that out, Sven. Looks like this might be the one! Thanks for watching my ramblings too, mate!
I don't quite understand how the voltage at point D can be -15V and the voltage at point F can be +2V when they're both derived from the same negative supply. Voltage F needs to be positive to bias V5, but I'm struggling to see how it ends up at 2V given where it's coming from.
Think about what happens in a conventional cathode biased stage. The plate voltage 'drags' the cathode towards it. The same is happening here, it's just starting from a negative voltage instead of ground.
@@BradsGuitarGarage Thanks for replying, Brad. That does make sense, it's just that I haven't seen bias implemented in quite that way before. You're absolutely right about Mesas being a nightmare to work on. I have a Studio Preamp I'm trying to refurbish, but the amount of work you have to put in just to get the PCB out of the chassis is just crazy, and the board is so stuffed it's very hard to change anything without damaging it. And, to top it all, most of the part numbers are beneath the component, so once the component is in place, you can barely read it. Jeez...
its 4 months later - how did the story end up ?? Will there be a part 2 ? ( appreciate what you've done so far ...) BTW - I have the 110V model ( 117V on spec sheet ) model running in Oz via a step-down transformer. I'm told that the fitted US transformer was one of the few mesas that can be reconfigured for 230-240V ( death cap removal noted), as well as main lamp rewire ( one end to primary centre tap)
I finished the job a few days later, but was running short of time, so I didn't do a video. The jobs come first and the video is just a bit of fun. Follow me up on the Facebook page if you want me to check out your amp and you're in the Sydney-ish area.
Hi, which is the balanced valve socket?
What do you mean by "balanced valve socket"?
Just revalving my Studio 22 and one of the 5 new ecc83's has a sticker on the side of the box that says 'balanced'. I think this the same as phase inverter? If so which valve socket?
"Balanced" on a dual triode valve box indicates that it's a tested and selected valve with a close match between each triode. A bit unnecessary in a guitar amp in my opinion. As for the valve positions, refer to your amp model's user manual, but generally the phase inverter is closest to the output valves.