Roadking I - Progressive Linkage Issue?

[fredderson]

Hi Guys,

First post here for me, usually I am able to find the answer buried somewhere but this time I’m stumped. Any tips or advice would be much appreciated!

I’ve got a Roadking I and seem to have a problem with the progressive linkage, as far as I can tell. It’s not the usual “pop” or “click” noise you get when you first switch channels after kicking it on. When I switch into the 3rd channel I get a severe volume drop; it occurs with all possible tube combinations, and ONLY on the third channel. Then, when I switch out of the third channel there is a very noticeable delay from the time I hit the switch to the time the channel actually changes (on my pedal or manually with the knob on the back). This delay ONLY occurs when I change OUT of channel 3. For example changing from 1 to 2 or 4 to 1 does not have a delay in the transition.

I think I’ve ruled out tubes as the issue here as all tube combinations work with channels 1, 2, and 4; be it 4 6l6s, 2 el34s, 2 6l6s and 2 el34s, etc. Everything’s glowing nicely under the hood, and I cannot see signs of degradation to any of the pots, caps, resistors, wires, etc, but maybe I’m not looking for the right thing. I’m no expert but I like to think I'm fairly competent.
The issue occurred suddenly during a jam. I shut it down nicely and then did some testing later. No blown fuse.

Thanks!

 

[mansfieldguitars]

With so many features it's real hard to diagnose without having the amp to check voltages and so forth. One thing you can try is to probe around the amp with a wooden chopstick while the amp is powered on and in play mode. This would help to locate any loose connections.


Start with this and if there's no change we'll see what else we can try

John

 

[fredderson]

Hi John,

Thanks for the tip! I will give it a try asap.

I spoke with Mesa customer support today and they thought that it could a be relay getting locked up when switching channels. To me this seems the most plausible explanation for the issue based on what I have found. I am not 100% familiar with electronic components and don't exactly know what type of relay is in the amp, let alone what it might look like or where it is located. I want to say that its a latching relay based on the Wikipedia article on relays and the light clunking noise the amp makes when switching channels.

Mesa advised taking in the amp for servicing, but I'm a D.I.Y. kinda guy and was hoping to learn a bit more about my amp and fix er' up myself. If anyone might know where the relays are located in the amp that would be great! Even if you might know what they look like (possibly with a pic?). I've tried looking for some schematics of the amp but no luck so far. The "poking" method might help me locate it. Worst case I'll cough up the money and have it fixed. Lucky for me there is an authorized Mesa service centre down the street.

Thanks again!

 

[fredderson]

Off the to the service centre it is! I don't have the tools required to take care of this job. For anyone who is interested; I think have found the relays, was fairly easy with a little guidance from a pal of mine. They are NEC MR301-6HSL relays and are located just behind the speaker outputs (the little grey boxes in the red rectangle in the picture).

Cheers'

 

[Monsta-Tone]

I think those relays are just for the speaker cabinet selection.
If you look on your board, where the arrow is that you drew, you will see some short orange rectangles. These should be the relays for channel and mode switching.

It does sound like one of them is sticking. FWIW, they have been using those same relays in their amps for many years. Some of my amps are about 15 years old and the relays are still going strong. Must be a fluke.

A good tech should be able to fix it right away.