Need some big help restoring my Tremoverb (strange mods)

[JustPassingThrough]

Hi guys,

I got my Tverb around 2018. I got it cheap because sometime prior to my ownership it was taken to a tech for a motorboating issue. This tech presumed it was the tremolo circuit and "disconnected" the tremolo. That didn't fix it, the owner was refunded and then took it to another tech. This tech diagnosed a fault around V4 that needed resoldering so that's what they did.

The tremolo still doesn't work though. I got in touch with the first tech and he said he couldn't remember what he did. I've no idea what's happening here and I'd very much like to reinstate this beast back to former glory.

As such, here's what I'm dealing with and I'll try and annotate where I can, but Mesa's lack of designators (R1, C1, Q3 etc) is proving a stumbling block.

Firstly there's a 1M resistor with the north pad seemingly drilled out. From looking at other PCBs this 1M should connect there, but I obviously can't. I'm trying to work out where it does connect so I can send it there.

You'll notice the north end is connected to a new network which connects to a 0.002uf capacitor (more on that later). Then this network of 1M resistor and 2nf cap is connected to a pad next to the 47k there by the white wires. Why? Who knows. I can't seem to track it to where it goes by testing its continuity around the board.

If I can work out where the 1M north side goes I think I can redirect it there with some heat shrink and micro surgery.

PROBLEM 2:

That yellow cap. I can't see this cap on any PCBs or schematics and it's definitely added in there. Again, I don't know why.

You can see it's connected to a pad near that 47nf up there (poorly replaced) and I can't detect where that trace goes when it heads north out of the shot. It's the one here with the clear tube around it. I lose that trace under the other components and cannot ascertain where it's headed or why it heads there.

There's also a random 100uf/50v cap which is another interesting development.

I have replaced LDR21 with a like for like from Xvive.

If anyone can help I'd greatly appreciate it. I did email Mesa, they weren't much help tbh but I understand this is rather bizarre with limited info.

I think primarily I need to work out what that drilled out pad was for the 1M, and then what that yellow cap is for and if it can be removed, but I don't think I'm experienced enough with this circuit to really know.

All help greatly appreciated. This has been bugging me since 2018 when I bought the amp!

If you need any other photos no worries.

The documents are here:

https://el34world.com/charts/Schematics/files/Mesa_boogie/Boogie_tremoverb.pdf

 

[JustPassingThrough]

OK. Some progress (?). I buzzed around and found this:

The new cap and the raised side of the 1M are going to pin 3 of V6.

The leg on the right of the yellow cap buzzes with all those pins of all those tubes which makes me think it's some sort of ground reference.

The other side of the 1M (not raised) has come loose from it's pad and will need to be reconnected... but I need to work out where it goes

 

[clutch71]

Very unfortunate. Looks like someone was trying some mod by numbers or a lazy tech tried fixing things without removing boards. It may not be a bad idea to review old threads on this forum to see if anyone was monkeying around lol.

Regardless, it looks like you have a lot going on and the cost of fixing may be more than the value of the amp. I would locate a reputable mesa service technician and see what they have to say,

 

[JustPassingThrough]

I don't think it'll be that bad. It's one pad drilled out, which means 1 trace/net. If I can find where that 1M connects I can reroute it easily enough and then see what that yellow cap is all about, but suspect it can be removed. The amp works great otherwise.

 

[clutch71]

I don't think it'll be that bad. It's one pad drilled out, which means 1 trace/net. If I can find where that 1M connects I can reroute it easily enough and then see what that yellow cap is all about, but suspect it can be removed. The amp works great otherwise.

Well that's good. Those old Tremoverbs were great. I had a buddy that had one but man was it a beast to lug around! Def an amp where casters are a MUST!

 

[JustPassingThrough]

So mesa got in touch with me. They sent me some diagrams of the Tremoverb PCB and where things were going.

They were totally wrong and not only contradicted their own schematic but made the amp inoperable and also sent 400v across the phase inverter. They suggested wiring the 10k resistor in parallel with the 1m (that lives across pins 2 and 3 of v6a) to pin 7 of the PI tube socket thereby connecting pins 2 and 7 of the phase inverter together.

Do not do this.

That was a lot of headache I didn't need and honestly you'd think they'd know better. If I didn't know what little I know I'd potentially be out hundreds of dollars at the tech, whereas I'm only out a fried tube that didn't like waking up to 402v in the morning.

So, that problem fixed I'm back to square one with an inoperable tremolo but everything checks out for continuity and is receiving healthy voltage. My only suspicion is the vactrol there. It's some xvive repro of a vtl5c9 but I suspect it's way off in terms of spec so a replacement will be sought.

By the way, the end of that yellow cap not connected to the PI tube socket goes to ground. This cap is not on the schematic but is in the mesa boards. It goes from pin 7 to gnd.

 

[domct203]

Man that is some serious hack work there. It’s stories like this that has made me pull the chassis of any used amp I buy and scan for shade-tree tech work.

I’m sure you don’t want to, but you should consider pulling that entire board. Whoever was in there was not skilled at all with a soldering iron, there could be lifted or broken traces on the other side.

I can’t think of a single reason to drill out a pad like that unless it was fubar from the repair.

Good luck, I wish I could be more help.

Dom

 

[JustPassingThrough]

Yeah it's not great. Although tbf it has survived tours and gigs without issue (tremolo aside).

I removed it and rebuilt it in a nicer way though and siliconed down anything that needs to float. There's a torn up trace below that 47nf there that I needed to circumvent.

This is Mesas totally wrong information for any future people. Do NOT wire that 10k to the tube pin as depicted. This is total madness and I really expected more diligence on their part.

I still have no tremolo but at least now I have a working amp again.

What's weird is that everything in the trem circuit has continuity, voltage, the correct parts, but there's no trem. Maybe the vactrol needs replacing but it's very difficult to find a reliable LDR of that spec these days.