Dual Rectifier Roadster technical problems

[apg3soup]

Hello--I bought my MESA about a year ago and have been having some trouble with it lately. I had it fixed but I fear my problem is resurrecting, I will attempt to portray my problem as best as possible so please bear with me.

About 7 months in, I noticed while playing in the Footswitch mode (activated on the rear panel), channels 3 & 4 on the footswitch were giving me problems. When I am playing, if I am in channel 4 on the footswitch, I can see flickering in channel 3 on the amp head. If I am in channel 3, I can see flickering in channel 2 on the head. It usually happens after playing for longer than 10 minutes Flickering = the channel that is not selected is briefly lighting up and then going dark again (fast like you would flick on and off a light switch). And yes I am aware of all the recommendations for warming up the amp slowly.

This all worries me because when the problem first started occuring months back it began to KICK to lower channels, literally jump from a higher channel to lower without me pushing anything on the footswitch. When it finally jumps I would no longer have access to channel 4 on my footswitch (IE--if I punched 4 on my footswitch it would only bring me to 3). Channels 1 and two worked fine, sometimes hitting 3 went to 2 (sometimes 3 went to 3), and hitting 4 always went to 3.
I had my head repaired by a certified MESA electronics handler around my area (this was about a month ago I turned it in and just got it back last Friday). They said there was something wrong with the footswitch, though when I tested it on another MESA head it worked fine and never did any kicking. They also said (and this was via advice from MESA themselves) that it was a problem with a relay switch. We figured this out because I called MESA and explained this problem to them and they guessed it would be a relay switch... They replaced the stuff and got it back to me and then...
I plugged in, jammed out for a bit, and the FLICKERING came back. I'm worried it is only a matter of time before it starts kicking and screwing up again and not letting me access channel 4 when in footswitch mode. It is more obvious when I have the master output up around 11 or 12 O'clock and activating reverb and/or solo mode on the footswitch while in channel 3 or 4. It also happens more when in BOLD and occasionally in Spongy if I have the output volume up higher.
I should also note that when I am accessing channels from the rear panel (IE selecting any channel to use by itself alone, and am not in footswitch mode) there are no problems with the channels or any flickering. They play great as a matter of fact and I want it to be that good while I'm using the footswitch pedal so I can access the solo boost, reverb, and an FX loop (not to mention jump between channels, at my desire that is)
Any other technical advice I can provide is this:
I use a Marshall 1960 lead 4x12 cab. It has options to play with 4 Ohm or 16 Ohm when using mono, I don't use it for stereo. I have used from 4 Ohm to 4 Ohm (MESA to Marshall), 8 ohm to 16 ohm (mesa to marshall, labeled as a safe mismatch in the owners manual for the roadster) and 16 Ohm to 16... I have tried using only the 50 watt selection for each channel, but it flickers in either 50 or 100 watt. Using the two El's or the 4 6l6 tubes doesn't matter either...it will flicker in footswitch mode no matter what, and since I just had it repaired, I can't figure out why. Has anybody experienced this problem, or have any idea what might be wrong? I just want my MESA Dual Rectifier Roadster to rock as much as the rest of yours. Thanks for reading, hope all is well with everyone.

I should also add I have never done anything drastic concerning any of the volume controls (master, gain, solo, reverb, presence, etc...)

 

[apg3soup]

Not sure if anyone is keeping up with this thread, but just updating. I talked to MESA and we have decided to send it in and have them take a look at it. I'll write up later what the problem is in case someone down the road seems to have the same situation.

On another note - this is why I choose MESA. When you buy their product you get great service from them in return, this is a major plus to their already great reputation. I'm excited to get my gear back in a few weeks and working again. `Tim Anderson

 

[domct203]

I know this is a very old thread, but I’m having the same issues with my Roadster. The amp switches channels perfectly with the rotary selector switch and the external trigger jacks, but when using the foot switch I get the same issue as the OP. It’s not the foot switch as I have another Roadster and confirmed the foot switch works fine on that amp.

I had been playing the amp for years in a MIDI rig using the external trigger jacks and a Voodoo Labs Control Switcher with zero issues. I’m downsizing and now trying to use the foot switch and I have the extra flickering lights exactly as described in the first post.

I hope someone can help.

Thanks,
Dom

 

[Eevil]

I know this is a very old thread, but I’m having the same issues with my Roadster. The amp switches channels perfectly with the rotary selector switch and the external trigger jacks, but when using the foot switch I get the same issue as the OP. It’s not the foot switch as I have another Roadster and confirmed the foot switch works fine on that amp.

I had been playing the amp for years in a MIDI rig using the external trigger jacks and a Voodoo Labs Control Switcher with zero issues. I’m downsizing and now trying to use the foot switch and I have the extra flickering lights exactly as described in the first post.

I hope someone can help.

Thanks,
Dom

Howdy

can you measure a channel switch voltage pin from footswitch and from the amp?

Just an idea: if the voltage has fluctuations in FS and not in the amp itself the connector pin may be dirty/oxidised in the amp. If the voltage fluctuates when measured from the amps circuit board then there’s something else amiss…

Working inside the amp may prove to be a lethal hobby so don’t do it if you’re not familiar with that stuff already

 

[blackmountainamps]

I know this is a very old thread, but I’m having the same issues with my Roadster. The amp switches channels perfectly with the rotary selector switch and the external trigger jacks, but when using the foot switch I get the same issue as the OP. It’s not the foot switch as I have another Roadster and confirmed the foot switch works fine on that amp.

I had been playing the amp for years in a MIDI rig using the external trigger jacks and a Voodoo Labs Control Switcher with zero issues. I’m downsizing and now trying to use the foot switch and I have the extra flickering lights exactly as described in the first post.

I hope someone can help.

Thanks,
Dom

I serviced two of these amps this year with the exact same issue but different causes. One of them was on my bench yesterday. The problem you are describing sounds more like a bad 7-pin footswitch cable which was the case of one of the amps I worked on. Try measuring continuity from on end to the other. The issue the OP was mentioning though was likely a problem with the diodes that are located in the switching board on the back of the amp.

 

[domct203]

Thanks for the replies!

I cleaned the DIN jack with DeOxIt, and confirmed the Foot Switch and Cable as good. I checked continuity on the cable (what a pain that was) and confirmed both Foot Switch and cable was good with another Roadster head.

I could see bad diodes being an issue. Too bad I can’t find a schematic. I have no issues checking voltages, I understand how to properly drain the filter caps.

Any tips on where to start checking?

Dom

 

[Eevil]

Maybe

Thanks for the replies!

I cleaned the DIN jack with DeOxIt, and confirmed the Foot Switch and Cable as good. I checked continuity on the cable (what a pain that was) and confirmed both Foot Switch and cable was good with another Roadster head.

I could see bad diodes being an issue. Too bad I can’t find a schematic. I have no issues checking voltages, I understand how to properly drain the filter caps.

Any tips on where to start checking?

Dom

Maybe the switching logic part is not so different in Road King II

(which can be found from the nets)

 

[blackmountainamps]

Sorry

Thanks for the replies!

I cleaned the DIN jack with DeOxIt, and confirmed the Foot Switch and Cable as good. I checked continuity on the cable (what a pain that was) and confirmed both Foot Switch and cable was good with another Roadster head.

I could see bad diodes being an issue. Too bad I can’t find a schematic. I have no issues checking voltages, I understand how to properly drain the filter caps.

Any tips on where to start checking?

Dom

Sorry I thought I had replied yesterday but I now realized I replied to the "noreply" email address that sends the notifications...

Anyway...here's what I wrote:
Yes, it's a pain to check that cable. If you ask mesa I believe they will send you the schematics. However, try doing this: have all channel switches on the back of the amp in "down" position. e.g. 50W

Then measure all the diodes in the board the switches are connected to. They should read voltage only one way. You can alternatively try to connected the footswitch to the amp and have the switches in the back in the down position, then start switching them up. If the footswitch misbehaves only when the back switches are in certain position, one or more diodes are certainly the problem. The other option is considering those diodes are cheap and you can replace them from the top of the board, you could replace them all. They are 1N4448

 

[domct203]

Sorry

Sorry I thought I had replied yesterday but I now realized I replied to the "noreply" email address that sends the notifications...

Anyway...here's what I wrote:
Yes, it's a pain to check that cable. If you ask mesa I believe they will send you the schematics. However, try doing this: have all channel switches on the back of the amp in "down" position. e.g. 50W

Then measure all the diodes in the board the switches are connected to. They should read voltage only one way. You can alternatively try to connected the footswitch to the amp and have the switches in the back in the down position, then start switching them up. If the footswitch misbehaves only when the back switches are in certain position, one or more diodes are certainly the problem. The other option is considering those diodes are cheap and you can replace them from the top of the board, you could replace them all. They are 1N4448

Thank you very much!

 

[domct203]

I haven’t opened the amp up yet to get voltage measurements but the switching continues to flutter regardless of the positions of the channel strip switches, up or down, and in every combination I tried.

Things to note:
The amp works fine for the first 5 minutes or so of playing before this relay/ch light fluttering starts.

Today I was playing in ch 3 for a good 10 minutes and when I went to switch to ch 4 the amp acted like it was stuck in ch 3. The led on the foot switch changes but the amp’s ch 4 led flickers dimly but the ch 3 light stays brightly lit and the amp stays in channel 3 with weak flickers of the ch 4 LED. If I switch to channel one, then switch to ch 4 it does the same thing, the ch 4 LED on the amp flickers dimly but the ch 3 LED comes on strong and the amp is in channel 3, even though the foot switch says it’s ch 4.

If I am playing in ch 4 when this relay fluttering starts happening the amp cuts out as it tries to flip between channels 4 & 3. The relays can be heard chattering during this.

Sometimes when I’m in ch 3 the channel 2 light flickers but the relays don’t start chattering.

The amp always works correctly with the rear channel selector switch and the foot switch disconnected.

If I let the amp cool down for twenty minutes or so the cycle repeats.

I’m hoping to get a copy of the schematic over the weekend, then I plan to check some voltages.

Any more ideas of what I should be checking for?

Dom

 

[domct203]

Well I got that schematic today. Looks like all the foot switch channel switching is controlled by an IC, and the circuit is a bit above my hobby skills LOL.

Just emailed my tech, I’ll be dropping the amp off after Christmas, should have it back within 3-weeks. I’ll follow up in the thread when I get it back.

Dom

 

[AndrewB]

@domct203 , glad to get your amp sorted today. Enjoy and stay in touch!


-------
Been on this board 14 years, 1st post, serious lurker!

 

[domct203]

Thanks Andrew. Played the amp for almost two hours without a single hiccup.

Anyone in CT/MA/RI/NY area, Andrew at Bell Audio Lab is the man for your sick amp! He stayed on my amp until he got this sorted.

Dom

 

[bandit2013]

For those looking for the schematic, search for the Road King series II. You will not find one for the Roadster if it exists. Why the back panel works and the footswitch does weird things: I have yet to find any schematics for the footswitch itself.

• The rotary control on the back panel forces the channel buss to be fixed to ground when set to the selected channel.
• If set to FS, the ground circuit is moved to the DIN 1 pin. I would assume this is where the control needs to be if you were to opt for the external jacks.
• The rotary or fixed channel mode and the ext jacks are hard shorts to ground.

Why the footswitch works differently. Reason for the ghosting channel LEDs and why it may operate in poltergeist mode (changing channels on you).

• The footswitch uses a single wire to control the selection of the 4 channels. This would be DIN pin 3. It is a DC voltage signal that selects the channel using an LM3913 LED driver.
• https://media.digikey.com/pdf/Data Sheets/Texas Instruments PDFs/LM3914.pdf
• If the signal voltage on DIN pin 3 is not stable, it can shift from channel to channel.
  • Channel 4 will have the highest voltage, Channel 3 will be lower and so on.
  • The cap on the signal line may be degraded or the connection to pin 3 is not ideal. This could also be a loose ground connection.
  • I would assume that the footswitch uses a cascaded diode array to make the different voltages.
  • If the footswitch cable is too long, this can also complicate things and add to some voltage losses on the DIN pin 3.

The same method is used in the Mark IV, and Mark V. For all I know it may not be caused by the channel switch circuit. There is a chance the 5V regulator is not keeping up or is not getting fed the proper voltage to maintain stability. What feeds in front of the LM7805 in the power circuit is the 12V DC regulator. This supplies V1 and V2 with heater voltage. It could be time for a CAP job (at least the one for the 12VDC regulator.

Din Connections
1 GND
2 (not mentioned in the schematic)
3 channel selection DC voltage
4 (not mentioned in the schematic)
5 solo
6 (not mentioned in the schematic)
7 reverb
8 mute

The three pins not mentioned in the schematic would have the following connections

• +12VDC source used for the LEDs
• +5VDC source for the channel selection circuit (I am making this assumption that there is a 5V reference since the channel selection will not be higher than 5V.
• FX loop on/off

Never really managed to go any deeper than that. Never had an issue with mine, yet.