Hoping for some repair help.
I have recently obtained an Ashdown Rootmaster MAG420 1x15 bass combo for free, as a repair project. The combo is in excellent condition for being probably 10 years old, very clean, and with no missing knobs or exterior damage. But the guy I got it from told me that his bass player had plugged it in one day to play and got a bang and blue flash. He obviously hadn't plugged it in since.
Taking a look inside, I see that the amp uses an Anaview ALC0300-1300 power supply and amp module, datasheet attached. From what I can see online, these were once well-regarded, but Anaview and its successors have been swallowed up by acquisitions, and no support or replacements are available.
I inspected the interior of the amp very closely for signs of damage from the flash and bang that was mentioned, he had indicated it was near the mains input, but other than the main fuse being blown I could see no damage. I am not an electronics engineer, but I have done some basic repairs, soldering etc. although not on amps and power supplies like this. But I tested for short circuits on the main inputs and outputs of the PCB, and even PAT tested the whole amp, it passed no problem. The fuse on the amp/power supply PCB was not blown. So I wondered if the flash had just been a bit of an extra surge blowing the main fuse.
So I bit the bullet, put a new fuse in, plugged it in and flipped the switch. Sure enough, huge bang and flash, the main fuse blew, the breaker of the socket blew, and then I saw damage! It was at the corner of the PCB where the flash had been. in addition to some pics of the amp interior generally, and some closeups of the damaged area, I put a pic of this damage below, after I had cleaned it a little with a brass brush. I'm not 100% sure but fairly positive it did not arc from this point to the ground connection point which is surprisingly close, as you can see in some of the pics. But I still can't see any clearly damaged components, just the area of the board. I noticed that the one solder point of the large capacitor nearest the damaged area looks a little stressed. Could it be that this cap is bad? How would I test for this? I did test and it is not shorted.
Can anyone give me some tips on what the issue may be, or what to test next? Or does someone have a working ALC0300-1300 module in the UK that they are looking to sell? I would really really love to get this combo going, as it's in great nick otherwise, and has all the features I am looking for. I am really hoping to repair this myself, although I suppose I could ship it to a repair house, but that could cost more than the amp is worth...
I have recently obtained an Ashdown Rootmaster MAG420 1x15 bass combo for free, as a repair project. The combo is in excellent condition for being probably 10 years old, very clean, and with no missing knobs or exterior damage. But the guy I got it from told me that his bass player had plugged it in one day to play and got a bang and blue flash. He obviously hadn't plugged it in since.
Taking a look inside, I see that the amp uses an Anaview ALC0300-1300 power supply and amp module, datasheet attached. From what I can see online, these were once well-regarded, but Anaview and its successors have been swallowed up by acquisitions, and no support or replacements are available.
I inspected the interior of the amp very closely for signs of damage from the flash and bang that was mentioned, he had indicated it was near the mains input, but other than the main fuse being blown I could see no damage. I am not an electronics engineer, but I have done some basic repairs, soldering etc. although not on amps and power supplies like this. But I tested for short circuits on the main inputs and outputs of the PCB, and even PAT tested the whole amp, it passed no problem. The fuse on the amp/power supply PCB was not blown. So I wondered if the flash had just been a bit of an extra surge blowing the main fuse.
So I bit the bullet, put a new fuse in, plugged it in and flipped the switch. Sure enough, huge bang and flash, the main fuse blew, the breaker of the socket blew, and then I saw damage! It was at the corner of the PCB where the flash had been. in addition to some pics of the amp interior generally, and some closeups of the damaged area, I put a pic of this damage below, after I had cleaned it a little with a brass brush. I'm not 100% sure but fairly positive it did not arc from this point to the ground connection point which is surprisingly close, as you can see in some of the pics. But I still can't see any clearly damaged components, just the area of the board. I noticed that the one solder point of the large capacitor nearest the damaged area looks a little stressed. Could it be that this cap is bad? How would I test for this? I did test and it is not shorted.
Can anyone give me some tips on what the issue may be, or what to test next? Or does someone have a working ALC0300-1300 module in the UK that they are looking to sell? I would really really love to get this combo going, as it's in great nick otherwise, and has all the features I am looking for. I am really hoping to repair this myself, although I suppose I could ship it to a repair house, but that could cost more than the amp is worth...
I've looked again at this amp with a friend who has some experience, and I'm starting to think I was wrong - I think that the bang I saw, and possibly the one experienced by the previous owner, was simply arcing from the high voltage area of the PCB to the very nearby (bit of a design flaw actually) ground connection. On inspection of the damaged area, after removing a little of the surface of the PCB, it looks to me like it's a single area of copper, so no arcing between areas of copper on the board. This area of the board is the power supply area so must have some fairly high voltages, indeed there is a warning on the board that the two fixing points in this area of the board must be insulated, which Ashdown seemingly ignored since both points had the same steel standoffs and screws as the other fixing points. And the standoff nearest the ground point had at some point broken off of the chassis so that corner of the board where the damaged occurred was not supported at all. It really looks as though maybe a very hard shock to the amp such as it being dropped could have made the corner of the board come in contact with the ground fixing screw, and cause damage to the PCB, and then arcing occured the next time power was applied. Below is the best picture I have showing how close the damaged area is to the ground screw, does that look like a distance that could arc across? I did discover that the exposed foil in the damaged area is directly connected to the black ceramic capacitor near the bridge rectifier and to the DC output of the rectifier itself, which is before the transformer in the circuit, so clearly the voltages there will be very high.
So my plan now is to move the ground point to a new hole a good few inches away from the board, remove the one remaining steel standoff from the power supply area of the board, replace it and the one already broken off with nylon standoffs of the same height that I happen to have in stock, and then re-insulate the damaged area of the PCB with hot glue. And then give it another try.
I have also contacted Ashdown, and have had a very helpful response from a tech there. However they say that they can't supply me with the schematic of the amp since it's IP protected, and that since the amp has been out of production for 6 years they can't supply spares (not sure why a long out of production amp is IP protected still). They have offered to fit or supply a different replacement module for 'around £100', which is an option, but if my hunch above is correct then I would save that £100...
I could also ask Ashdown if there is a precedent for failure of this type in this amp.
But the one other thing I'm thinking about is if possibly the large main electrolytic caps have shorted, since they are obviously also very near the damaged area. Could shorted caps cause this sort of failure? And if they had shorted, could they still appear to be in pristine condition with no bulging or burned areas around the base or anything? I don't have a lot of experience with this type of failure, but I do know it could happen. I would be very appreciative of anyone's observances or hunches having looked at the pictures.
So my plan now is to move the ground point to a new hole a good few inches away from the board, remove the one remaining steel standoff from the power supply area of the board, replace it and the one already broken off with nylon standoffs of the same height that I happen to have in stock, and then re-insulate the damaged area of the PCB with hot glue. And then give it another try.
I have also contacted Ashdown, and have had a very helpful response from a tech there. However they say that they can't supply me with the schematic of the amp since it's IP protected, and that since the amp has been out of production for 6 years they can't supply spares (not sure why a long out of production amp is IP protected still). They have offered to fit or supply a different replacement module for 'around £100', which is an option, but if my hunch above is correct then I would save that £100...
I could also ask Ashdown if there is a precedent for failure of this type in this amp.
But the one other thing I'm thinking about is if possibly the large main electrolytic caps have shorted, since they are obviously also very near the damaged area. Could shorted caps cause this sort of failure? And if they had shorted, could they still appear to be in pristine condition with no bulging or burned areas around the base or anything? I don't have a lot of experience with this type of failure, but I do know it could happen. I would be very appreciative of anyone's observances or hunches having looked at the pictures.
So the end of the story on this one was that I had to replace the amp module.
As in my last post, I did try to move the ground screw and reinsulate the damaged area of the PCB, but it was very obvious right away that the arcing is between points on the board itself. I did PAT test again before applying power, and it passed with no issue, so I'm not sure I understand why it then arcs when mains power is applied. I'm sure there is someone who has read this here who understands this more than I do....
Anyway, in the end, I managed to obtain a replacement Anaview module, actually a slightly older one. All I will say is to put in a plug for Ashdown, they really stand behind their products.
So now I have this other module that seems unobtainium, and is at least visually in really good condition, apart from this one area where it arcs...if anyone is interested.
As in my last post, I did try to move the ground screw and reinsulate the damaged area of the PCB, but it was very obvious right away that the arcing is between points on the board itself. I did PAT test again before applying power, and it passed with no issue, so I'm not sure I understand why it then arcs when mains power is applied. I'm sure there is someone who has read this here who understands this more than I do....
Anyway, in the end, I managed to obtain a replacement Anaview module, actually a slightly older one. All I will say is to put in a plug for Ashdown, they really stand behind their products.
So now I have this other module that seems unobtainium, and is at least visually in really good condition, apart from this one area where it arcs...if anyone is interested.
Have you checked the varistor on the card....Black disk with 2 legs....
If the amp has suffered a surge in the electrical network, the varistor short-circuits to blow the fuse and thus protect the rest.
The diode bridge can also be shorted.
If the amp has suffered a surge in the electrical network, the varistor short-circuits to blow the fuse and thus protect the rest.
The diode bridge can also be shorted.
@mamocel thanks for the reply! I looked at the black discs with two legs (there are two of them next to the bridge rectifier), they're labelled 'NTC 4.0' and searches indicate that they are in fact thermistors. measuring across them without removing them from the circuit shows a resistance of around 5 ohms on both, one is 5.0-5.1 and the other is 4.8. So they are not directly shorted. Measuring all combos of the 4 pins of the bridge rectifier next to them shows open circuit on all.
what else can I measure to pinpoint the issue? is it worth removing the thermistors to measure them, or does that fact they show a resistance near to what they should be mean that they are not the issue?
what else can I measure to pinpoint the issue? is it worth removing the thermistors to measure them, or does that fact they show a resistance near to what they should be mean that they are not the issue?