Mesa Rectoverb 50 --- 3V DC circuit issues

[Bishop]

Anyone ever had issues with the Mesa-Boogie 3V circuit?

I'm having intermittent problems with a Rectoverb 50.

At first I thought the 3V circuit was only for the DC heater on V1, but upon further inspection it's also used for the relay coils. Due to the PCB style troubleshooting seems like it would be a nightmare.

Being intermittent should I be looking at the transistors first?

https://schematicheaven.net/boogieam..._rectoverb.pdf

page 5 and 7 are where the 3V circuit is shown.

Any insight massively appreciated.

[Enzo]

No, being intermittent you should look at connections first.

While anything is possible, transistors do not generally fail, heal themselves, fail, heal themselves, and so on.

[Mick Bailey]

What's the exact nature of the problem? Without knowing what the symptoms are it's difficult to offer specific advice.

[Bishop]

What's the exact nature of the problem? Without knowing what the symptoms are it's difficult to offer specific advice.

The signal dies, both channel LEDs die. The heater on V1 goes out, I think I can hear a relay click.

no voltage on the +\- 3VDC circuit.

[Mick Bailey]

I'd start by monitoring the voltage off the bridge rectifier circuit. If it drops there you probably have a diode or solder joint issue in that area.

[drewl]

The bridge rectifiers that convert the filament voltage from ac to dc break down over the years.

They power the preamp filaments and the switching circuits.

They probably look discolored, and start to burn the pc board.

When replacing them, mount them off the board a bit to prevent further board damage.

[Bishop]

The bridge rectifiers that convert the filament voltage from ac to dc break down over the years.

They power the preamp filaments and the switching circuits.

They probably look discolored, and start to burn the pc board.

When replacing them, mount them off the board a bit to prevent further board damage.

This was actually my first thought before making this post and strangely enough all 4 diodes in the rectifier measure at .1V (in circuit, with the diode setting on a meter). I went ahead and replaced them, but I get the exact same results with new diodes, while the old diodes measure at the normal .6V out-of-circuit. I ordered e-caps for the +/- 3V circuit and have already pulled them successfully, so we'll see on that soon, but my confidence is low. I originally thought the 3V circuit was only for the DC heater so that's why I thought it had to be the caps after trying the diodes.

Even before replacing the diodes I did spend some time trying to poke around for a bad joint on the PCB with no luck, I'll try that again once I have the new caps in (if that doesn't solve it).

[Mick Bailey]

Getting the same 0.1v reading across every diode should have suggested there was an other reason for this - it's unlikely that all 4 would fail in an identical way, and even more so that the forward voltage would be that figure. The usual failure mode is shorted, or more rarely, open-circuit (which would give other symptoms). Diode problems are usually not intermittent. My feeling is the caps are not the issue either - the only cap failure type that would cause the supply to drop is a short, and result in a lot of heat or smoke as a result.

Rather than replace components, measure the voltages during failure to determine where the problem lies. Is the AC getting to the bridge? Is there DC coming out of it?. Is just one side failing and you're only losing the + or - voltage, or is it both?

[Enzo]

Tube heaters as well as the low voltage transformer winding have very low resistance. If you don't remove the tubes first, I am not surprised your readings are low.

[Bishop]

Tube heaters as well as the low voltage transformer winding have very low resistance. If you don't remove the tubes first, I am not surprised your readings are low.

The tubes are indeed removed and the 6.3vAC is working. Currently has same diode readings even with transformer winding removed (in order to flip the PCB) Both - and + 3VDC voltage is missing from all points of the amp.

Hadn’t intended on just swapping parts, but like I said, on my first round of troubleshooting I missed the fact that the 3V circuit was used for more then just DC heater.

[Enzo]

I was referring to your diode drops reading low, sorry.

[Bishop]

I was referring to your diode drops reading low, sorry.

No worries, that's what I thought and what I was responding to. The diodes still have a low drop in circuit even with no tubes, and the 6.3 winding pulled.

I was also responding to the previous post from yours about the 6.3AC, which is working and getting to the rectifier.

[g1]

The diodes still have a low drop in circuit even with no tubes, and the 6.3 winding pulled.

There are also the 150 ohm 'center-tap' resistors, and 39 ohm from each side of 3VDC lines to ground that must be considered.

[Bishop]

There are also the 150 ohm 'center-tap' resistors, and 39 ohm from each side of 3VDC lines to ground that must be considered.

That’s right, I should have mentioned, the CT ones are 100 ohm and measure OK. I think the 39 ohm resistors are 100 ohm as well, which measure OK also, but I need to follow the traces to double check that’s them. I couldn’t find any 39 ohm resistors.

[The Dude]

If memory serves, that board is double sided. Maybe you have connection issues and/or feedthrough holes were damaged when diodes were replaced or traces damaged from heat. I'd check continuity from lead to lead in the circuit and make sure a connection isn't missing.