Bass-Thing Posted December 16, 2015 Share Posted December 16, 2015 I've got a PF500 that has been causing me problems for ages. I used to play it through the flip top PF250HE and it used to cut out at high volumes. The tech who tested it reached the conclusion that there was something wrong with the cab because the amp would only cut out when it was attached to the cab. If you left the lid off and played it through the cab it was fine, likewise played through other cabs. Anyway I was satisfied it was in very good nick so I sold it on eBay. To cut a long story short it was returned to me and had clearly been damaged. There were deep scratches on both the top and bottom of the amp like it had been dropped down a concrete stairway. Something was rattling around inside. The buyer claimed he had started playing through it and it had blown up. I assumed the fuse had been blown but weirdly enough, it fired up ok and seemed to be working fine (through my Hartke Hydrives (410 &115). I had it checked out. The rattling was a blown capacitor. The input transformer also appeared to have been 'super hot' at some point. The capacitor was changed twice and each time it blew again shortly after power up. Weirdly enough it still works!!! I'm not sure what to do. Can anybody tell me what the f*** is going on??? I feel inclined to sell it again for parts or repair with the added caveat that it still actually works. Any advice on what to do would be much appreciated. I have already considered taking a sledge hammer to it... Quote Link to comment Share on other sites More sharing options...
Mudpup Posted December 16, 2015 Share Posted December 16, 2015 PF500s have a bad rep for blowing up unfortunately - do a search on here or the USA site...... You may struggle to move it on here Quote Link to comment Share on other sites More sharing options...
Bass-Thing Posted December 17, 2015 Author Share Posted December 17, 2015 [quote name='Mudpup' timestamp='1450301472' post='2931580'] PF500s have a bad rep for blowing up unfortunately - do a search on here or the USA site...... You may struggle to move it on here [/quote] Their terrible rep is something I've picked up on and I wouldn't try to sell it on here. I'm just trying to ascertain whether or not it's worth fixing. If there's a way of stopping the capacitor from blowing that's not ridiculously expensive, I'd like to know. Quote Link to comment Share on other sites More sharing options...
Bigwan Posted December 17, 2015 Share Posted December 17, 2015 It's maybe not rated to a high enough voltage. You could try replacing it with a higher voltage one. Quote Link to comment Share on other sites More sharing options...
Bass-Thing Posted December 17, 2015 Author Share Posted December 17, 2015 [quote name='Bigwan' timestamp='1450334973' post='2931722'] It's maybe not rated to a high enough voltage. You could try replacing it with a higher voltage one. [/quote] Thanks for that though I'm not really sure what you mean. Do you mean a higher voltage capacitor? Incidentally I've had a good look through the site and although there are lots of references to PF500 'horror stories' I can't find any of the stories themselves. Maybe I'm not looking back far enough. I bought the amp new from the USA on eBay about 4 years ago so it would have been one of the early ones that were prone to problems. Quote Link to comment Share on other sites More sharing options...
Bigwan Posted December 17, 2015 Share Posted December 17, 2015 [quote name='Bass-Thing' timestamp='1450366026' post='2932092'] Thanks for that though I'm not really sure what you mean. Do you mean a higher voltage capacitor? [/quote] Yes, caps have a voltage rating. It's possible the cap in question is underrated, or it may point to a fault down the line causing the voltage across the cap to be higher than it was rated for. A decent tech should be able to tell you what's going on. Quote Link to comment Share on other sites More sharing options...
Twincam Posted December 17, 2015 Share Posted December 17, 2015 Yeah you can over spec a cap. You could try using one of higher voltage rating but a similar capacitance rating. Or even try one of higher both values. This might work. Quote Link to comment Share on other sites More sharing options...
Ghost_Bass Posted December 17, 2015 Share Posted December 17, 2015 before replacing the cap for a "bigger" one you should find out what's causing them to blow in the first place. reinforcing that cap could make another component the weakest link in the chain and consequently blow up (and it could be more expensive to replace than a cap). Quote Link to comment Share on other sites More sharing options...
stevebasshead Posted December 17, 2015 Share Posted December 17, 2015 [quote name='Ghost_Bass' timestamp='1450367705' post='2932108'] before replacing the cap for a "bigger" one you should find out what's causing them to blow in the first place. reinforcing that cap could make another component the weakest link in the chain and consequently blow up (and it could be more expensive to replace than a cap). [/quote]This... At best, replace with one with the same voltage handling and capacitance values in case the cap that blew was simply defective. If it blows again you know you have an issue somewhere in the circuit prior to it that you'll need to have investigated. Quote Link to comment Share on other sites More sharing options...
Twincam Posted December 18, 2015 Share Posted December 18, 2015 [quote name='stevebasshead' timestamp='1450372738' post='2932176'] This... At best, replace with one with the same voltage handling and capacitance values in case the cap that blew was simply defective. If it blows again you know you have an issue somewhere in the circuit prior to it that you'll need to have investigated. [/quote] Yes this is also very true and was going to mention this in my previous post. Putting in a bigger cap could cause issue else where! It's a gamble. Quote Link to comment Share on other sites More sharing options...
petetexas Posted December 23, 2015 Share Posted December 23, 2015 Ive had a pf500 ( about 4 years now ) with no problems . I sold it once ( on here ) only to find that the guy I sold it to said it kept cutting out ! I refunded his money , got the amp back , and I really "pushed " at a volume . NO PROBLEM ! I got it checked out at Polar Audio , who ran it for a whole day , and found no problem . I recon the guy read all the horror stories , and did not want to trust it , so said it was cutting out . Its now used as a back up ( take it everywhere I gig - and had to use it on three occasions when my Peavey T-Max cut out ) Got my T-Max repaired , and sold it on , now got a pf800 as my main head , with no problem . Quote Link to comment Share on other sites More sharing options...
Guest bassman7755 Posted December 23, 2015 Share Posted December 23, 2015 (edited) [quote name='Twincam' timestamp='1450445043' post='2932909'] Yes this is also very true and was going to mention this in my previous post. Putting in a bigger cap could cause issue else where! It's a gamble. [/quote] There are actually relatively few circumstances where you can raise a capacitance rating and it not have an adverse effect on a circuit. Transformer power supply ripple smoothing caps are one of these few circumstances (but even then in moderation). I'm guessing the PF500 is a class D / switched mode PSU design in which case it would almost certainly be a bad idea to change a value randomly. Edited December 23, 2015 by bassman7755 Quote Link to comment Share on other sites More sharing options...
JapanAxe Posted December 23, 2015 Share Posted December 23, 2015 [quote name='bassman7755' timestamp='1450888926' post='2936767'] There are actually relatively few circumstances where you can raise a capacitance rating and it not have an adverse effect on a circuit. Power supply ripple smoothing caps are one of these few circumstances (but even then in moderation). I'm guessing the PF500 is a class D / switched mode PSU design in which case it would almost certainly be a bad idea to change a value randomly. [/quote] Increasing cap sizes in a smoothing circuit can caush bigger currents to flow through the rectifier diodes, which may result in 'magic smoke'! Quote Link to comment Share on other sites More sharing options...
Guest bassman7755 Posted December 23, 2015 Share Posted December 23, 2015 [quote name='JapanAxe' timestamp='1450889103' post='2936771'] Increasing cap sizes in a smoothing circuit can caush bigger currents to flow through the rectifier diodes, which may result in 'magic smoke'! [/quote] Indeed which is why I said "in moderation", but yeah best left alone unless you really know what you are doing. Quote Link to comment Share on other sites More sharing options...
markorbit Posted December 24, 2015 Share Posted December 24, 2015 Send it or speak to an Ampeg Service Center. Quote Link to comment Share on other sites More sharing options...
BigRedX Posted December 24, 2015 Share Posted December 24, 2015 From what I have seen, these amps are extremely fussy about what cab(s) you plug them into especially when running into a 4Ω load, where one setup may work fine and another will keep cutting out. IMO the amp is only worth the time and money it will take to fix it, if you intend to keep and use it as your main amp. In that case get it repaired by Ampeg and get a guarantee on the repair. Otherwise sell it for "spares or repair" on eBay. You'll be surprised by how much non-functional equipment sells for on there, especially that with a well-known brand name. I had a similarly poorly Ashdown Superfly (sported all the classic Superfly maladies - high pitched whistle on the output, random failure to power up) and it still sold for £75 which considering it was EOL'd at £199 was well worth my time and effort to get it listed. Quote Link to comment Share on other sites More sharing options...
Guest bassman7755 Posted December 24, 2015 Share Posted December 24, 2015 [quote name='BigRedX' timestamp='1450943296' post='2937147'] Otherwise sell it for "spares or repair" on eBay. You'll be surprised by how much non-functional equipment sells for on there, especially that with a well-known brand name. I had a similarly poorly Ashdown Superfly (sported all the classic Superfly maladies - high pitched whistle on the output, random failure to power up) and it still sold for £75 which considering it was EOL'd at £199 was well worth my time and effort to get it listed. [/quote] Theres a lot of people making a living by buying and repairing stuff on ebay. Quote Link to comment Share on other sites More sharing options...
Bass-Thing Posted December 28, 2015 Author Share Posted December 28, 2015 [quote name='BigRedX' timestamp='1450943296' post='2937147'] From what I have seen, these amps are extremely fussy about what cab(s) you plug them into especially when running into a 4Ω load, where one setup may work fine and another will keep cutting out. IMO the amp is only worth the time and money it will take to fix it, if you intend to keep and use it as your main amp. In that case get it repaired by Ampeg and get a guarantee on the repair. Otherwise sell it for "spares or repair" on eBay. You'll be surprised by how much non-functional equipment sells for on there, especially that with a well-known brand name. I had a similarly poorly Ashdown Superfly (sported all the classic Superfly maladies - high pitched whistle on the output, random failure to power up) and it still sold for £75 which considering it was EOL'd at £199 was well worth my time and effort to get it listed. [/quote] Thanks for that. Very sound advice indeed (no pun intended honest ). I am going to sell it on for spares/repair. The main selling point will be that it still appears to be working normally which is bonkers but there you go. I've now got a Bugera Veyron Tube as my portable option and it's so much better than the PF500 in every way, so I wouldn't want to spend more money on it when ultimately I want to sell it on regardless. Thanks for all your help on this one folks. Much appreciated! Happy new year! Quote Link to comment Share on other sites More sharing options...
Chienmortbb Posted December 29, 2015 Share Posted December 29, 2015 I am not clear where the caps are, in the mains side or secondary side but either have the same issue. Increasing the cap values will increase inrush current and is likely to cause problems elsewhere. The first thing to do is find out what revision your board is and then find out if it can be updated to the latest revision. Contact Ampeg as it was a manufacturing defect and they may/should help even though you did not buy it here. Finally or maybe firstly, check the labels to ensure it was designed to work on 230V 50Hz Quote Link to comment Share on other sites More sharing options...
Bass-Thing Posted January 4, 2016 Author Share Posted January 4, 2016 [quote name='Chienmortbb' timestamp='1451412219' post='2940300'] I am not clear where the caps are, in the mains side or secondary side but either have the same issue. Increasing the cap values will increase inrush current and is likely to cause problems elsewhere. The first thing to do is find out what revision your board is and then find out if it can be updated to the latest revision. Contact Ampeg as it was a manufacturing defect and they may/should help even though you did not buy it here. Finally or maybe firstly, check the labels to ensure it was designed to work on 230V 50Hz [/quote] Thanks for that. It's definitely designed for 230V because the fuse has a selector switch. Anyway I'm going to pass it on now and sell it for parts/repair. It's not as good as the Bugera amps I have anyway. Shame because the flip top is a great idea. Quote Link to comment Share on other sites More sharing options...
Ghost_Bass Posted January 5, 2016 Share Posted January 5, 2016 Just to clarify, when i commented about using a "bigger" capacitor i wasn't talking about raising the capacitance, only raising the voltage, (ie: replacing a 10uf 5v cap with a 10uf 16v will work, if the system is working fine, but the new cap will take more voltage before it blows wich means that any other component in the circuit that won't take this kind of voltage will blow before the new capacitor and could be a more expensive component to replace) Disclaimer: i'm not a tech and my knowledge of these things is very limited to the simple basics, take my post with a spoon of salt. Quote Link to comment Share on other sites More sharing options...
Bass-Thing Posted January 26, 2016 Author Share Posted January 26, 2016 Sold it for parts or repair. It's being used as a pre amp now and the new owner is happy as a pig in poo poo! Don't you just love a happy ending? Quote Link to comment Share on other sites More sharing options...
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