I have broken my amp, yes it is my own fault.

Haych

Never one to leave things alone I thought I’d do a bit of “preventative maintenance” on the HRD. 

A few weeks ago I had the thing apart to install a few mods. While I was at it I managed to break one of those horrid ribbon cables that connect the two boards together so I did a bit of a make-do repair while I got some proper wire in to fix it properly. 

I was also concerned about the other cables that I didn’t break as I was obviously putting quite a bit of stress on them and taking the board out to fix the make-do repair would put more stress on them, so while it was in pieces again I decided to “fix” them all. 

Everything seemed to work well for a few days and I even felt a bit smug about it, in the most humble way possible of course. 

Then two days ago I was testing a new pedal I acquired and I pushed the button to go from yellow to green channel and the amp started emitting the most horrible and loud buzzing noise. Even with nothing plugged in it was making the most awful racket. 

However, if I use input 2 instead of input 1 the noise goes away and everything works normally again, except for  being in the low gain input. 

So I whipped the back off again to take a look, thinking that there was a short to earth on input 1, but everything looks alright. With the back off I power it back up again and the amp works perfectly, no noise, no fuss, sounds awesome!

Very carefully I replace the back cover of the amp with it still turned on and as soon as I push it home the buzzing returned. Hey, what!

Take it off and buzzing stops. So it seems that I’ve either “fixed” in a fault while replacing the above mentioned wires, possibly got a couple of solder joints too close to each other, or the new wires don’t like being close to the metal plate on the inside of the rear cover. 

Perhaps there’s a reason Fender (and others) use that horrible stiff ribbon cable after all, as it will keep a shape once installed in the amp. Individual 22awg wires won’t keep a shape. 

Is the close proximity of the wires to the rear shielding the most likely culprit or is it more probable that I’ve just FUBAR’d it with dodgy soldering (I actually think my soldering is very good as I used to do it for a living). 

I’ve narrowed the fault down to be in the bunch of wires second from the right as you look at the rear of the amp with the back removed. I can’t replicate the fault with the back off even if I give the wires a good nudge (with something non-conductive, of course).

Now, last question; is there anywhere I can purchase some of that awful stiff ribbon cable? <sheepish grin>

One day I will learn to leave stuff alone if it’s working ok, but this is a flaw in my character I’ve had since I could hold a screwdriver, I’m afraid. I just like fiddling and taking stuff apart. 

Most of the time I can put it back together again and I like to think I have a pretty good track record of It working again after the fact, this instance just isn’t one of them. 

Modulus_Amps

fuzz dog supply ribbon cables as an option with kits, they may have something suitable for you

For your noise you have to isolate the part of the amp causing it, The quick and dirt way to do this is to pull pre amp valves, starting at v1

Haych

Modulus_Amps said:

fuzz dog supply ribbon cables as an option with kits, they may have something suitable for you

For your noise you have to isolate the part of the amp causing it, The quick and dirt way to do this is to pull pre amp valves, starting at v1

Thank you. Much appreciated. I’ll check out fuzz dog and start pulling valves tomorrow. Cheers. 

donbot

How did you get on with this? I have some ribbon cable at work from internal scsi cables that should do the job. You’d need to cut it to length and width with the correct number of conductors. Happy to ship it out to you if you think it will help...

Haych

donbot said:

How did you get on with this? I have some ribbon cable at work from internal scsi cables that should do the job. You’d need to cut it to length and width with the correct number of conductors. Happy to ship it out to you if you think it will help...

Thanks @donbot, all seems to be ok for now though.

The problem was persistent every time I put the rear cover back on the amp so I figured it was definitely something to do with the "preventative maintenance" I did, the wires just didn't like being in closer proximity to each other and/or the shielding inside the back plate of the amp.

I did try fuzz dog for the ribbon cable but they weren't able to help so I phoned around a few amp repair places who told me that the ribbon cable in question is not a part/cannot get/is not available etc.  I find this odd since Fender can obviously get it from somewhere and I'll bet the house they don't make it themselves, but still, the short answer was 'sorry, can't help you'.

Before this no-help from reputable amp repairers I'd already thought of a contingency.  The wires clearly don't like being close to one another and don't like being close to the shielding so the obvious answer was to just mod the mod.  So I shortened the wires and routed them directly into the top of the tube board, with a small piece of heat shrink over the solder joint, instead of routing them to pass through the underside of the board as per the original design - this means they don't need to snake around the edge of the board close to the shielding and can be kept more or less parallel to one another as the original ribbon cable also facilitated.

In the end it was also the easiest thing to do as it meant I didn't have to take the board out of the amp again - 20 minutes with a soldering iron, solder sucker some snips and a heat gun and it was all done and is now working perfectly.

I do enjoy fiddling with stuff, even at the risk of breaking it.  One day I will learn just to accept that it's probably better to leave things alone if they're working ok, but I'm glad I was able to fix it all the same.

Thanks for your kind offer though, much appreciated.