Ashdown Abm Evo Ii - Cutting Out

[CXIII]

Hi folks, anyone have a similar experience with the problem described below?

I've an Ashdown ABM Evo II 500 amp that is intermittently cutting out every so often. There is still input signal from the bass just no output and usually a simple off/on reboot will solve the problem (although not always). I'm running it through an Ashdown 410t and TE 1518c cab, both input/output dials usually sit between 10/12 o'clock) - have checked all leads, bass battery (mute button) etc and they are all fine. Straight of after reading some other users Ashdown problems that it was the effects loop either connections or pcb but that board seems to be working fine when I hooked up a pedal through it. I opened up the amp, all connections/wires/fans/solder joins etc seem fine. The cutting out seems to happen when I press the flat/shape button while amp is on (but not all the time) and I also noticed recently that if it does cut out cranking the input dial up to full seems to get everything going again.

I've emailed ashdown who basically said you need to get this checked out (duh). Being based in Belfast shipping the thing over to Ashdown and back again is going to be costly so was wondering if anyone here has had the same problem or has an idea of what the problem could be so I can either repair it myself or drop it in to a repair shop here with a specific-ish diagnosis (because as I say the problem is intermittent so the amp could seem fine to techs over here).

Any help would be appreciated.

[icastle]

[quote name='CXIII' post='1099664' date='Jan 23 2011, 02:29 PM']The cutting out seems to happen when I press the flat/shape button while amp is on (but not all the time) and I also noticed recently that if it does cut out cranking the input dial up to full seems to get everything going again.[/quote]

Intermittent faults are the absolute pits.

Taking a stab in the dark and assuming your EVO is out of warranty...

You could narrow it down - try tapping around that input control and give it a little 'wiggle' the next time the amp dies to see if it miraculously comes back to life - if it does then chances are you've got a bad joint in the area you were tapping.

If so, you (or someone else) needs to get to the underside of that board and check that the connections from the pot are well soldered - in fact I'd just remove the original solder and resolder it again just to be sure.

[CXIII]

[quote name='icastle' post='1099680' date='Jan 23 2011, 02:44 PM']Intermittent faults are the absolute pits.

Taking a stab in the dark and assuming your EVO is out of warranty...

You could narrow it down - try tapping around that input control and give it a little 'wiggle' the next time the amp dies to see if it miraculously comes back to life - if it does then chances are you've got a bad joint in the area you were tapping.

If so, you (or someone else) needs to get to the underside of that board and check that the connections from the pot are well soldered - in fact I'd just remove the original solder and resolder it again just to be sure.[/quote]

Yeah its well out of warranty.

I've been trying to get the amp to 'die' all morning to do exactly as you say and try to narrow down the source of the problem - no luck yet...(don't know if thats good or bad).

[flyfisher]

[quote name='icastle' post='1099680' date='Jan 23 2011, 02:44 PM']Intermittent faults are the absolute pits. [/quote]
That's for sure.

My old Ampeg combo started doing a similar thing a couple of months ago and gradually got so bad it was unuseable - which actually helped the diagnosis.

I removed the amp and, by hanging a meter on the power rails quickly established that the fault was on the pre-amp board because the power rails would momentarily drop out, even though the power TO the pre-amp board (from the power amp board) was stable.

The pre-amp board had some voltage reduction circuitry, which seems like a good place to start looking, particularly around the two large high-wattage resistors that were only soldered onto the board and not mechanically supported in any other way (they weren't even in contact with the board, so were just supported by their wires). In a high-vibration environment, such a construction is not ideal and when I wiggled the resistor it was not firmly held in place by the wire at one end.

So, needing to look at the underside of the board, I removed it completely and discovered that the PCB pad around the resistor wire had come adrift from the board - probably, I guess, due to 35 years of heat from the resistor. This allowed the thin PCB copper trace to move with the vibration of the combo and ultimately break.

The fault was intermittent because although the track was broken the two pieces were being held together by the stiffness of the resistor wire, but there was enough movement to allow the track to become disconnected intermittently. Heat from the resistor probably had an effect as well.

So, I scraped off the solder resist from the PCB track (the green coating on the solder side of a PCB) and soldered a short piece of solid wire from the resistor leg to the newly exposed (and solidly stuck down) PCB copper track. I also did the same thing with the other high-power resistor legs just in case they were also about to fail in the same way.

After reassembling it all, it has been working fine for the past couple of weeks.

In my experience, intermittent faults are usually mechanical in nature, especially if the basic electronic design is good and there are no issues such as overheating etc. Components themselves are usually pretty reliable (again, good design can be a big factor in this) and therefore rarely fail, and almost nevert in an intermittent fashion. My combo is about 35 years old, so it had already stood the test of time, suggesting the design itself is good, which really only leaves a mechanical fault - as I discovered.

The point of this ramble is to highlight that you don't always need to be an electronics expert to fix music gear. Because of the life our gear tends to lead, the majority of problems are mechanical - jack sockets, cables, and in this case a broken PCB track. A bit of careful examination and common sense, plus being a bit handy with a soldering iron, can work wonders.

[icastle]

[quote name='flyfisher' post='1099745' date='Jan 23 2011, 03:41 PM']The point of this ramble is to highlight that you don't always need to be an electronics expert to fix music gear. Because of the life our gear tends to lead, the majority of problems are mechanical - jack sockets, cables, and in this case a broken PCB track. A bit of careful examination and common sense, plus being a bit handy with a soldering iron, can work wonders.[/quote]

+1
I spent a few years as a service tech and then service manager for a sound and lighting company and what you say is pretty accurate in many cases.
The problem with internet as a support medium is that you can never judge the electronic expertise or experience of the person you are talking to.

I'm always happy to explain how to do something to the nth degree but I'm always very aware that I may be sending someone down a path that they might get halfway down and fall off!
I'm by no stretch of the imagination a 'sensitive' person, but I'd hate someone to make a dreadful mistake and make things ten times worse because I either forgot to mention one thing that I thought was obvious or made incorrect assumptions about experience and ability.

So - if I come across as condescending on occasion when discussing technical practicalities (as I'm often accused of being in 'real life'), it's never done in malice - I'm just trying to make sure I'm not making things potentially worse for the OP...

[CXIII]

After tinkering with the amp for the best part of today I've finally narrowed down the source of the problem. There is definitely something wrong with the input jack. Most times I unplug the the guitar lead from the amp and back in again the signal cuts out altogether or will die a fair bit and only when the input dial is cranked fully can you hear anything and its quite static sounding. The other strange part is that when I unplug again from the amp and in again it doesn't sort out the problem (maybe 1 in 6 does unplugging from amp works) whereas in nearly all 'attempts' unplugging the lead from the bass and in again results in signal coming back fully. I've cleaned the amp input jack which as done jack. To me it does seem like a surge problem? What tell tae signs should I be looking for on the pcb for blown components?

[flyfisher]

A lot of good points there, [b]icastle[/b]. I guess my point about "common sense" was made in the hope that people should know their own limitations and that they shouldn't do anything they don't feel sure about. Opening up an amp and having a close and careful look around won't do any harm, but might reveal the problem - especially if it is mechanical.

I understand the concern about not really knowing the experience of people seeking advice but my view is that if they are asking then it's up to them what they do with it. The alternative is to always recommend shipping the gear in question to a "qualified expert", in which case no one ever learns to fix anything - which does seem to be an increasing trend these days. A great shame in my opinion.

I suppose it won't be long before someone is sued for giving advice over the web without highlighting a whole host of frankly obvious safety measures, just because some dimwit decided to open up an amp and stick their fingers in the power supply.

On that note, my lawyer has advised that I should point out that using your tongue is not a safe substitute for a good multimeter when trying to measure potentially dangerous voltages inside electronic equipment. Just in case someone out there didn't realise.

Edited January 23, 2011 by flyfisher

[flyfisher]

[quote name='CXIII' post='1100268' date='Jan 23 2011, 11:04 PM']What tell tae signs should I be looking for on the pcb for blown components?[/quote]
If it's an intermittent problem than I'd be surprised if it's a blown component. If a component dies it usually stays dead.

But if you do suspect a blown component then looking for scorch marks on the PCB can be a tell-tale sign that a component has seriously overheated, which is generally not a good thing. Electrolytic capacitors (usually in aluminium cans) can fail and even "pop" sometimes, releasing a very distinctive smell that's almost impossible to describe and also impossible to forget.

If you've narrowed things down to the input jack check that the jack is firmly fixed to the chassis of the amp. There's a lot of leverage on a jack socket and if it's not fixed securely to the chassis (usually by a retaining nut around the socket hole) then any stress and strain is transferred directly to the PCB (assuming it's constructed that way). This can lead to PCB track problems like the one I described in my Ampeg combo.

If the jack is not mounted directly onto a PCB then it should be pretty easy to remove it and wire-in a new one.

[icastle]

[quote name='flyfisher' post='1100280' date='Jan 23 2011, 11:17 PM']On that note, my lawyer has advised that I should point out that using your tongue is not a safe substitute for a good multimeter when trying to measure potentially dangerous voltages inside electronic equipment. Just in case someone out there didn't realise.[/quote]

Yep.
Takes ages to dig your fillings out of the plasterwork if you do that

Incidentally, if anyone is about to use a 'multimeter' that looks like this.... don't

[icastle]

[quote name='flyfisher' post='1100291' date='Jan 23 2011, 11:28 PM']Electrolytic capacitors (usually in aluminium cans) can fail and even "pop" sometimes, releasing a very distinctive smell that's almost impossible to describe and also impossible to forget.[/quote]

Also a sticky residue around the base (do NOT be tempted to lick your fingers - just trust me on this!) or cotton wool type fluff all over the place.