Problem with Rocktron R120C

[Wicked_Tone]

First, I really appreciate the people on this forum and greatly value the suggestions and assistance you provide. I've had a Rocktron R120C amp combo for several weeks that I bought used and recently a problem has surfaced. When I play on the gain (dirty) channel, after about 10 minutes of playing the amp will briefly cut out completely with no sound and within 2-3 seconds the sound returns. This will happen intermittently once the amp has been running 10+ minutes and continues to cut out in the same way if you remain on the dirty channel going through either the high or low input. This problem doesn't occur on the clean channel at all through either of the inputs. I opened up the amp and tried resoldering the switching components and input jacks, but the problem continues. I'm not sure if this is related to the preamp section or power section at this point? Any help would be immensely appreciated.

[Wicked_Tone]

I have ruled out problems associated to a bad guitar cable or guitar itself by using different cables and guitars. I also sprayed tuner cleaner on the 1/4 guitar jack and inserted and removed several times in low and high input jacks. I also cleaned all pots with tuner cleaner as well. Speaker connections are solid as well.

[J M Fahey]

If sound cuts off on the dirty channel but not on the clean one, it's not a power amp problem.
Open the chassis amd lightly tap inside in different places with a chopstick or similar plastic element.
Can you make it cut?

[Enzo]

It MUST have something to do with the channel itself.  The speakers and their connections have no way to know which channel you are using, and cannot selectively drop out accordingly.  Same with the power amp.  If teh power amp were at fault, this would happen on all channels.

You probably have a thermally sensitive part, probably an op amp IC.   This is where we look at all IC output pins for unwanted DC offset, then get out the freeze spray and chill each part along teh board, looking for ones that are sensitive.  I bet that would find it.

[Roly]

If you don't have any freeze spray to hand and alternative is to dip a cotton bud in alcohol (metho) and dab it on the body of the suspect component, such as the op-amps, when the fault is apparent, and blow gently to evaporate the alcohol and chill the component. An ice cube in a plastic bag should also do the trick.  Allow a few seconds for the component to cool.  When you find the right one you should be able to bring the amp back to life on command.

[Enzo]

Actually, unless you are going for hard freeze, any aerosol spray is a chiller.  A can of the keyboard dust-off stuff, or some contact cleaner.

I'd be careful dropping alcohol on a live circuit, not only does some have water content, but it is flamable.


Sometimes even a small amount of cooling is enough to expose the problem area.

[Roly]

Don't know 'bout where you are but all pressure pack cans in Australia are now hydrocarbon propelled - so it's a choice between something like alcohol or something like propane.   

Metho being highly hydroscopic is a pest but new stuff is dry and as long as you keep it sealed up stays that way for a couple of months use, then I pour it into my truck petrol tank (to keep the system free of condensate) and buy a new bottle.

[J M Fahey]

Well, consider the bright side 
Any aerosol can plus a Bic lighter makes for an excellent Zombie repellent weapon 



Ok, ok, stop beating me, I'll change that  smilie for  :loco or even  :duh .... just stop being so  :trouble

[Wicked_Tone]

Thanks for the info guys! I'll check the ICs and report back later.

[Enzo]

Even a can of compressed air will chill.

[Roly]

Thanks for that though JM - I'll keep that in mind the next time I'm out in the field without my soldering iron (or attacked by zombies) ...

[J M Fahey]

Well, you Ozzies my need much more than a small flamethrower if you get caught on the wrong side of *THIS*:

And *you* explain others what it is  :lmao:

[Roly]

Uh, okay.  There are a couple of things it could be, but it's obviously a fence.

A little Aussie history is required.  The first industry to really take off after white settlement was raising sheep for wool.  In fact it was said for many years that Australia "rode on the sheeps' back", 'though this became progressively less true after the Second World War with a swing from primary to secondary industry.

There were a few problems running sheep in Australia, and one of them was the native wild dog, the Dingo, which not surprisingly considered a mob of sheep to be lunch on the hoof.  One response to this was to construct a dog-proof fence across a huge tract of the continent and basically try and obliterate the Dingo on the "inside".

While JM's picture is titled "Dingo Fence" I'm pretty sure it isn't, because I've been through the real thing a number of times and it's a lot taller, the fence above not being tall enough to keep a Dingo out.


"Camerons Corner at the intersection of New South Wales, Queensland and South Australia. The Dingo fence seen was originally constructed to keep rabbits out, however it was later used to keep dingoes out of sheep farming areas. The fence stretches some 5,500 kilometres and is the longest fence in the world."



{the sharp eyed will notice there are two "longest fences in the world", both in different Australian States  }

While I'm wary of any native animal that lives around tourist hot spots and picnic grounds, I have simply dossed down beside the vehicle in desert country with no worries, and even had Dingos come right into my camp for water with no problems at all.  Wild pigs are a very different matter.

The fence shown in JM's post however is to meet a different problem entirely of the settlers own making - rabbits.  In the early days there were "Acclimatisation Societies" that decided that the Aussie native wildlife wasn't good enough, and imported wildlife to "improve" it, mainly from England.

They liked a spot of huntin' and fishin' so they imported rabbits, foxes, carp (goldfish) and sundry other critters.  The first couple of bunches of rabbits they imported were established in Geelong, not far from where I now live, but they died (or were hunted) out.  So they brought in another bunch.

This time it quickly turned into a nightmare horror story - the rabbit took to Australia as rabbit heaven and in only a few years had grown to literally plague proportions across the country, adapting from the Snowy alps to the burning Simpson desert, and were rapidly crippling agriculture and eating the native animals out of house and home.

In Western Australia matters got so bad that they built a rabbit-proof fence to keep the little buggers out of the wheat growing country.  It isn't clear in JM's pic but almost half the fence is underground, extending in this case I think to the left (clue; the rocks placed along the bottom).



For the time, this was a mammoth undertaking...



...but one has to understand the seriousness and scale of the problem.  This gives some idea of the difference between the "outside" where the rabbits were and where this photograph was taken from, and the "inside", far side, where there were no rabbits.



It's hard to wrap your head around the fact that within a few years a few dozen rabbits had grown to several hundred million, were eating just about everything in sight, and just about everywhere was starting to look like this...



"within ten years of the introduction in 1859, rabbits had become so prevalent that two million could be shot or trapped annually without having any noticeable effect on the population. It was the fastest spread ever recorded of any mammal anywhere in the world."

Shooting was too expensive, and trapping and poison baits ineffective.  Farmers would organise "drives" to push thousands into a fence corner then dozens of men would wade in and spend days plucking them out, wringing necks, and skinning for fur and meat, but still they kept coming.  They became a primary source of cheap meat, felt, and there was a major export trade in their skins.



In one area of southern Australia cats were introduce as a control measure, but this only resulted in a secondary plague of cats that decimated the native wildlife.

In 1950 the CSIRO finally released Myxomatosis, a viral rodent encephalitis.  Within two years 99.8% of an estimated 600 million rabbits had died from the disease, and while they developed some resistance by the late 50's would never again reach such overwhelming numbers.

"The introduction of rabbit haemorraghic disease virus RHDV (also known as rabbit calicivirus) in 1995 again reduced rabbit numbers to very low levels, with greatest impact in arid zones and lesser impact in high rainfall areas.  RHDV is considered only the second successful control of a mammalian pest in the world."

While the rabbit can now be said to be under control there are still a range of other introduced pest species that aren't; horses, camels, goats, foxes, pigs, dogs, cats, deer, some birds, and sundry plant and insect species, and fish.

But the worst of all is the cane toad (Bufo marinus) introduced in 1935 to eat grubs that were damaging the sugar harvest on the Queensland coast.  Not only didn't the toads eat the cane grubs, they ate anything else they could get their capacious mouths around, and their toxicity killed anything that tried to eat them.   :duh



What this graphic doesn't show is that they have now spread right across the Top End (as we call it) to the far north west, hitching rides in cargo.  At this time we are in a similar situation to the rabbit before "myxie" came along, except that they are effectively useless for meat or skins, toxic, even more fecund, and no fence seems capable of stopping their spread.

{now JM will introduce us to the Anaconda-proof fence  :cheesy:  after which normal service will be resumed}

[J M Fahey]

WoW !!!
Thanks a lot!!
Got much more than I bargained for.
I didn't know Ozzies had such a string of bad luck and horror stories about well meant animal imports.
A compact and powerful Ecology lesson.
Even The Simpsons have a chapter about it.

[Wicked_Tone]

Well guys, I checked the ICs and now the amp is working fine and I've played it several days through both the high and low inputs on the gain channel and the issue seems to have gone away. It's puzzling, but I may eventually solder in sockets and try different ICs in place of the current ones. Thanks again for all the help!