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Thread: Markbass Little Mark II

  1. #71
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    Quote Originally Posted by Justin Thomas View Post
    And as MarkusBass said - poorly qualified repair center, or my own opinion, charging way too much.
    They are not charging too much. They are simply not able to fix the amp (they don't have sufficient knowledge to do it) and they only can offer replacing the board with a new one (and $400 may be a real price of the module imported from Italy). Maybe Enzo, or Stan will be able to add their opinions. I think that this is typical policy of many manufacturers: don't spend time on fixing an amp, just replace the module that failed. In many cases this is a good policy but they didn't foreseen situation when the cost of a module is almost the same as the cost of the amp. This usually leads to customers turning to other manufacturers (who do exactly the same). The solution is simple; instead of trying to fix the amp with recommended by Markbass service centre, go to a local workshop that has experience with this brand. It's hard to believe that you cannot find such a workshop in the US.

    Mark

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    I will follow up with markbass. but simply the fact that I need to be pursuing this path is really too much. if these machines are sold as "good quality" (and the pricing is in the "good quality" range), I expect fair treatment. so far I do not see it that way. and, to be sure, the board did not show any burn marks prior to going in to the depot, and it was not popping fuses.

  3. #73
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    Quote Originally Posted by hitch View Post
    I will follow up with markbass. but simply the fact that I need to be pursuing this path is really too much. if these machines are sold as "good quality" (and the pricing is in the "good quality" range), I expect fair treatment. so far I do not see it that way. and, to be sure, the board did not show any burn marks prior to going in to the depot, and it was not popping fuses.
    I would inform Markbass about the situation. Most probably they will answer that the amp has to be fixed by an authorized service centre, the cost of the module is $300 and the rest is labour of the service. But you may let them know that you are not happy with this situation.
    The fact that the board is not burnt means that there is a big chance that it can be easily fixed. Where exactly are you located? I think that there are guys here from NY that most probably could fix it. Alternatively come to Poland and I will fix it for you .
    Fixing such an amp is (in general) difficult because amps are more and more complex, fixing them requires more knowledge, better tools and so on. Manufacturers should be interested in supporting their products but, as you can see, sometimes they are not. Turning to another amp brands may be a good sign for them (they may learn something).

    Enzo, I need your support here .

    Mark

  4. #74
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    Markus, you are referring to the entire amp board as a module. As far as I know, there is only the one board, so it is not really a module at all, it is everything (I'm speculating, maybe there's a preamp board too?).
    This is what Hitch complained of from the beginning, why ISN'T the SMPS it's own separate module? The fact that it is not leads me to believe they expect the SMPS will most often be repairable, unless the board itself is burnt beyond repair.
    So they need to know if their service centres are not repairing at a component level.
    Quote Originally Posted by Justin Thomas View Post
    In my ideal world, I'm not too loud - your room is too small!

  5. #75
    Senior Member Enzo's Avatar
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    The whole distinction between power supply and amp is artificial, they are all one thing. Just because many amps have segmented the functions doesn;t remove their intimate relation. WHy stop there? In a push pull amp, why not have separate push and pull side boards? And the SMPS? Ought not that be divided into primary side circuits - the switcher - and the secondary side supplies? Usually only one side has a problem. Or perhaps low voltage and high voltage on different boards? because really, it is very rare that both high and low voltage supplies fail at the same time.

    Look at discrete units out there. We have connectors between the sections failing, we are now dealing with very high frequencies, so board layout is MUCH more critical than it would be with a linear supply.

    We often look at things through out own glasses. Servicability is certainly important, but so is proper operation and reliability. The engineers are expecting the vast majority of these to work trouble free long term. And I suspect they will.

    This board takes power from the mains and sends it to a speaker. That is its function. we might want it to be split up so we can concentrate a bad part on a smaller surface. And we might really only be rationalizing ways to pay less. But it is still just one big circuit to convert power from one form to another. The desire to separate the left hand from the right is a human conceit.
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  6. #76
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    No arguement with that Enzo. My arguement is with the board swap approach (as opposed to component level servicing), such as the Ensoniq and Line6 service models. And if that is your service model, then I would propose the SMPS being a separate module.
    Quote Originally Posted by Justin Thomas View Post
    In my ideal world, I'm not too loud - your room is too small!

  7. #77
    Senior Member Enzo's Avatar
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    Why?

    A board swap is a board swap. Doesn;t matter how much or how little is on it. The unit won;t work without it either way.
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  8. #78
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    Cost. From what I can gather above, an SMPS module would be cheaper than what he will have to pay for the amp/smps board. At least going by other manufacturers that do not repair smps but replace them as modules.
    He is being asked to pay $400 for the repair. There are companies who do not service or provide documentation/parts to service their smps modules. I don't believe replacing their modules (separate SMPS) would be a $400 repair bill.
    But I don't want to drag this out. We can agree to disagree on this one point .
    Quote Originally Posted by Justin Thomas View Post
    In my ideal world, I'm not too loud - your room is too small!

  9. #79
    Senior Member Enzo's Avatar
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    The Ensoniq model at least was predicated on return of the defective board, which was repaired and returned to the rotation.

    Cost per board is pure speculation in this discussion.

    I have to remind that their cost is not what they charge. Look at something like the Fender FM212R. They find it cheaper to replace the whole amp than to pay me $50 to fix it.


    A while back I had a Nady wireless in for service, I asked for a schematic, and they told me no schematics and in fact they did not even have a service network., All repairs done at the factory. They quoted me a flat rate of $300 for the repair. I said to them, "But that is more than a new one." Their flat rate was what they would charge nonetheless. I told them I would then be forced to return the product to the customer as not repairable, and recommend he seek other brands for replacement gear.
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  10. #80
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    Quote Originally Posted by Enzo View Post
    The whole distinction between power supply and amp is artificial, they are all one thing. Just because many amps have segmented the functions doesn't remove their intimate relation. WHy stop there? In a push pull amp, why not have separate push and pull side boards? And the SMPS? Ought not that be divided into primary side circuits - the switcher - and the secondary side supplies? Usually only one side has a problem. Or perhaps low voltage and high voltage on different boards? because really, it is very rare that both high and low voltage supplies fail at the same time.
    Enzo made some very important points. Amps are sometimes divided into a separate boards but it is artificial. If you have capacitors on the output of the power supply, should they be in the power amp, or in the power supply? If you have a filter before the power supply, should it be on the power supply board, or rather with power switch? If you have 5W drop resistors (for +/-15V power supply), would you like to have them on a separate board (because the resistors often fail)? And then you end up with lot of connectors, which again may fail.
    Quote Originally Posted by Enzo View Post
    Look at discrete units out there. We have connectors between the sections failing, we are now dealing with very high frequencies, so board layout is MUCH more critical than it would be with a linear supply.
    Agree. The reliability (and layout) is most important here. All the manufacturers that I know manufacture their modules on one board. And there must be some reason for this. Also two separate modules would be more expensive and they would require larger enclosure (which again would make the cost of the amp higher).
    Quote Originally Posted by g-one View Post
    My argument is with the board swap approach (as opposed to component level servicing), such as the Ensoniq and Line6 service models. And if that is your service model, then I would propose the SMPS being a separate module.
    You have to distinguish between power amp (for example for bass guitar) having power above 500W (sometimes 1000W and even more), with huge currents between the power supply and the power amp and devices like multi-channel mixer without power amp. In the first case, separate power supply and power amp would be a very bad idea (taking into account reliability of the amp). In the second case quite often the power supply (SMPS) is a separate module and this is how many mixers are designed.
    Hitch has a powerful power amp for a bass guitar - this is the first case. The problem is how fixing of the amp is handled by the manufacturer. We all see that it could be done better than it is now.

    BTW, I had lately a small Line6 bass amp (15W). It consists of the preamp board (with DSP processor) and a small power amp module (TDA2030). The preamp has failed. Fixing the amp requires replacing the preamp which makes 90% of the amp. And the cost of the operation is higher than the cost of a new amp. The customer decided not to fix the amp (and buy another brand).

    Mark
    Last edited by MarkusBass; 09-17-2014 at 11:34 AM.
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  11. #81
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    Thank you and much respect to everyone posting in this thread!

    A Mark Bass Little Mark II just came across my bench and was blowing fuses and not powering up.

    Opening it up, I went through testing as many active components as possible on them main power amp/power supply PCB - desoldering connections to measure components out of circuit wherever possible. To do this test, I looked for reasonable voltage drops across diodes using a multimeter's diode test, I looked for shorts across pins in the voltage regulators and and I used the methods for testing MOSFETs described by Alan Wolke in this excellent video: How to test MOSFETs with a DMM - a few methods... - YouTube and alternately described in text form here: Testing a MosFet

    Going through the amp I found that one of the eight output MOSFETS seemed to be out of specification. I ordered a complete set of 4 IRFP9240 and 4 IRFP240 with spares so I could match the transistors as closely as possible (using the procedure described in this paper: http://www.firstwatt.com/pdf/art_matching.pdf ). I'm not sure how important it is to match these but the original transistors appeared to be labeled by MarkBass and it's just a few quick measurements with a multimeter.

    Replacing all 8 output MOSFETS worked out great and the amp is working as good as new and sounds quite nice. I've repaired countless tube amps, solid state power amps and other devices and I've been (and remain) a bit skeptical of the class D topology (from a sound quality and reliability perspective) and definitely hesitant to repair class D amps but repairing this amp was easier than expected.

    Hope this information may be of help to others down the road!
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  12. #82
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    Yes the power amp is pretty straight forward on that amp, simple in fact but the power supply and control circuits are another story. They are a nice amp when working but I have had troubles with several of them. Everything is component level repairs here since parts and boards are not possible to get.
    It is cheaper in the long run to replace boards since they do not need a service shop, or extensive parts stock if they only stock a limited number of different finished pc boards. As more and more equipment moves to Class D amps which have no manually placed parts on the boards or any expensive parts, board replacement will be the norm in countries were boards can be obtained.
    As switch mode power supply controllers keep getting getting more sophisticated part counts so way down so high power supplies get smaller, simpler and cheaper, those two will be dominate. I was starting to see a lot of Orange Terror Bass amps, tiny 4-5 lb 500 or 1000 watt amps. They are cheap, powerful and popular here. I was suspecting they were not reliable because I saw a lot of them but discovered that other techs were afraid of them and referred them to me. They are really simple, nothing as complicated as the first 2 generations of SMPS amps or Digital amps and in fact are as easy to repair as an old Peavey solid state amp. That is the wave of the future, the manufacturers must love the light, small low cost amps because they surely have a lower cost to build to ship and stock parts for.
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    Markbass repair update

    this is a followup to my travails in August/September with the mark bass combo unit amp.

    after much discussion, the local distributor very kindly agreed to have the unit repaired, and had a qualified depot replace the old board with a new board. at time of replacement, the repair shop also verified that the entire combo unit was behaving itself. ie, no shorts in the speaker, yada yada.

    the unit has been working well, mainly as a home studio practice amp, and has not been pushed. it has been used only with professional quality basses and patch cords, all of which have been used on other amps in the same time period with no issues.

    unfortunately, the MarkBass combo unit died again a few days ago. ie, no light, not sound, nothing. so the new install worked for about 2 months.

    which means another round of negotiations with both MarkBass and the local distributor. I really feel for the distributor. the issue appears to be product quality and product servicability. Markbass itself has not shown itself to be forthcoming for support to date. I hope they begin to show a different, customer-centric (or is that "product centric", really?) face.

  14. #84
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    Quote Originally Posted by hitch View Post
    this is a followup to my travails in August/September with the mark bass combo unit amp.

    after much discussion, the local distributor very kindly agreed to have the unit repaired, and had a qualified depot replace the old board with a new board. at time of replacement, the repair shop also verified that the entire combo unit was behaving itself. ie, no shorts in the speaker, yada yada.

    the unit has been working well, mainly as a home studio practice amp, and has not been pushed. it has been used only with professional quality basses and patch cords, all of which have been used on other amps in the same time period with no issues.

    unfortunately, the MarkBass combo unit died again a few days ago. ie, no light, not sound, nothing. so the new install worked for about 2 months.

    which means another round of negotiations with both MarkBass and the local distributor. I really feel for the distributor. the issue appears to be product quality and product servicability. Markbass itself has not shown itself to be forthcoming for support to date. I hope they begin to show a different, customer-centric (or is that "product centric", really?) face.
    Sorry to hear about this. Was there anything special when the amp failed? Of course, the amp should work also with any quality basses and cords . I found Markbass amp quite reliable and I'm curious what exactly happened. It can be something simple like open fuse, or something serious like failed power supply. Do they charge you for fixing the amp? I would try to find someone who is familiar with this amp , not necessarily authorized service center . I wouldn't feel sorry for the distributor. They take money for this. If they conclude that this model is not reliable, they should stop distributing it. In the meantime, they need to improve their customer-centric policy.

    Mark

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    thanks for the response. the amp just did not turn on. ie, it worked, and then the next time he went to use it, it did not turn on. no "event" happened, unfortunately.

    due to it being fixed recently by an authorized repair place, I don't want to go digging around, as i'd like to have the repair guy figure it out. unfortunately, the repair guy is on christmas holidays until January. which means there is no amp for this holiday season. so, it could be a fuse, but I really have to leave it alone. ie, if I mess with it, it could become my problem.

    the distributor took a board out of a new amp for the replacement, as they did not have any spare boards hanging around. and they looked after the cost, in spite of Markbass themselves not offering any support. so I do feel for the distributor.

    but having an amp that seems to die without warning or reason is disheartening, and makes it useless. ie, who would bring a flakey amp to a gig.

    again, thanks for your input. I do hope they figure it out. in the mean time, I am looking for other brands that might work. and that hopefully are sane with how the electronics are laid out. ie, made to be serviced efficiently, not made to be thrown out.

  16. #86
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    Hartle Kickback 15!

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    Modular and proprietary. We recently went through a situation where the power supply module gave out. Lead time on the replacement was 12 weeks but the repair facility noted that they had ordered the same part for another customer and it was 110 days back ordered.

    I mothballed the amp, a 1x12 combo, and am debating on whether or not to buy a used head to go in it.

    In the meantime, I bought a used GK fusion 550 which while being ridiculously complex is rock solid reliable.

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    update to the continuing saga of the dead board. the original amp board died. that was replaced by an updated new improved model. that board died within a month of use. a new board from a new "stepping" (ie a new improved board design) has now been provided to replace the replacement board.

    all I can say is that I no longer trust Markbass electronics. I also am getting tired of driving to the repair shop, even though the repair guy is a good guy. and I definitely need to maintain a separate operational amp at all times so that when (not if) the markbass dies, I have a fallback.

    the vendor for markbass has been very supportive through this, and markbass has not been supportive. my money will be on other brands from this vendor for future purchases.

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    I've enjoyed this discussion!
    And a MarkBass Little Mark tube 800 has begin to give me a headache!
    The customer brought it in with a high pitch oscillation around 15Khz and upon inspection there were about 4-5 frequencies riding on 125Khz switching frequency that were all on the output at about 800mv p-p. The transformer was even oscillating. I replaced it as a shot in the dark, then did a cap job. Nothing.

    Visual Sound Technologies sold me a replacement board and problem was gone. Tested the amp and played through it. Problem solved, right?

    Customer just contacted me, 30 min in to his first set on a bass solo, in which he admitted he used a Guitar boost pedal boutique, the oscillation started again. Now it's back?

    When I had it the first time I isolated the preamp and it was defiantly the SPS and Power amp section.

    What gives?

    Also, VST didn't know that these boards have inconsistent negative offset voltages on the outputs. The new one I ordered had -180Mv DC. They checked 2 of theirs and one had -6mv, while the other had -125mv.

    Anybody have a clue of how to stop this oscillation?

  20. #90
    Supporting Member Jazz P Bass's Avatar
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    It sounds like it is a power supply filtering problem.
    http://music-electronics-forum.com/a...rkii-combo.pdf
    Hopefully, the SMPS is the same.

  21. #91
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    I'll change the IRFP240 & irfp9240 damaged a Little Mark III. IRFP27n60K damaged too in power supply.
    Where I can measure the BIas to set the new transistors?
    The schematic of power amp very similar at little II.
    http://elektrotanya.com/parsek_mark_.../download.html
    Thanks

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    Hey there!!

    Need some help here..... A few weeks ago I had a Mark Bass Combo Head II in my bench with the fuse blowing. I opened it and started to measure the power MOSFETs. It uses 3 IRFP240 and 3 IRFP9240. One IRFP240 and one IRFP9240 were shortened. I also measured the other main transistors to ensure everything was ok, before turning the amp on, and found that the two MOSFETs (IRFP27N60K)in the SMPS were shortened too. I also measured the switiching diodes and all other caps and transistors. Nothing wrong. Replaced both of them, cleaned and changed the termic paste to ensure it would dissipate the heat correctly . Reasembled the whole amp and power it. Amp was sounding as supposed to. Called the customer and delivered the amp.

    To my surprise, the amp came back a few days later, with he same problem. Blowing fuse. Opened it and found the same issue. The two MOSFETs in SMPS were shortened as well as one IRFP240 and one IRFP9240 in the power section. This time, I replaced all the 6 MOSFETs in the power amp section as well as the MOSFETs in the SMPS. Turned the amp on and the issue was solved. Delivered it to the customer.

    Now, to my surprise, after a few more days, the customer told me the amp was blowing fuses AGAIN. Told him to bring it to me, and the same issue happened. Two MOSFETs in the SMPS and another two in the power amp section.

    I measured again all the power transistors, as well as diodes and caps. Nothing more is shortened or open. Everything seems to be fine, but my experience says that if replace those shortened MOSFETs, the amp will return again, cause I didn't find the actual problem. I also considered not using enough termic paste in the power MOSFETs, but after checking them again, everything is fine. Thanks to this thread, I found the schematics of this amp and tried to found any resistor or other component that are connected to those failing MOSFETs to find the cause of the problem, but nothing is wrong.

    Does anybody saw anything like that?

    I read on this thread, that an user had the power board replaced with a similar issue, and then the issue appeared again!!! Can't understand this.

    I live in Brazil, and we don't have any Mark Bass authorized tech. If I can't solve this issue, I don't see any other option then sending the amp to Italy, to Mark Bass (I contacted Mark Bass, and this was the suggested action by the manufacturer).

    Any help will be greatly apreciated.

    Thanks a lot.

  23. #93
    I'm a member? nickb's Avatar
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    My guess would that there is a problem with the power amp. Just to throw some suggestions out - Did you check the idle current? Does the fan operate correctly? Could there be a problem with the user's speaker cable ( intermittent short) or the speaker impedance too low?
    Experience is something you get, just after you really needed it.

  24. #94
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    Quote Originally Posted by Leooooh View Post
    Hey there!!

    Need some help here..... A few weeks ago I had a Mark Bass Combo Head II in my bench with the fuse blowing. I opened it and started to measure the power MOSFETs. It uses 3 IRFP240 and 3 IRFP9240. One IRFP240 and one IRFP9240 were shortened. I also measured the other main transistors to ensure everything was ok, before turning the amp on, and found that the two MOSFETs (IRFP27N60K)in the SMPS were shortened too. I also measured the switiching diodes and all other caps and transistors. Nothing wrong. Replaced both of them, cleaned and changed the termic paste to ensure it would dissipate the heat correctly . Reasembled the whole amp and power it. Amp was sounding as supposed to. Called the customer and delivered the amp.

    To my surprise, the amp came back a few days later, with he same problem. Blowing fuse. Opened it and found the same issue. The two MOSFETs in SMPS were shortened as well as one IRFP240 and one IRFP9240 in the power section. This time, I replaced all the 6 MOSFETs in the power amp section as well as the MOSFETs in the SMPS. Turned the amp on and the issue was solved. Delivered it to the customer.

    Now, to my surprise, after a few more days, the customer told me the amp was blowing fuses AGAIN. Told him to bring it to me, and the same issue happened. Two MOSFETs in the SMPS and another two in the power amp section.

    I measured again all the power transistors, as well as diodes and caps. Nothing more is shortened or open. Everything seems to be fine, but my experience says that if replace those shortened MOSFETs, the amp will return again, cause I didn't find the actual problem. I also considered not using enough termic paste in the power MOSFETs, but after checking them again, everything is fine. Thanks to this thread, I found the schematics of this amp and tried to found any resistor or other component that are connected to those failing MOSFETs to find the cause of the problem, but nothing is wrong.

    Does anybody saw anything like that?

    I read on this thread, that an user had the power board replaced with a similar issue, and then the issue appeared again!!! Can't understand this.

    I live in Brazil, and we don't have any Mark Bass authorized tech. If I can't solve this issue, I don't see any other option then sending the amp to Italy, to Mark Bass (I contacted Mark Bass, and this was the suggested action by the manufacturer).

    Any help will be greatly apreciated.

    Thanks a lot.
    the new MOSFETs that installed had the same gain 3? were they matched?
    the bias equal in all those transistors?

  25. #95
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    I had exactly the same experience.
    I found cold solder joints on some of the large film resistor packages. Reflow all the larger smd resistors and make sure the bias changes when you turn the bias pot.

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    Quote Originally Posted by nickb View Post
    My guess would that there is a problem with the power amp. Just to throw some suggestions out - Did you check the idle current? Does the fan operate correctly? Could there be a problem with the user's speaker cable ( intermittent short) or the speaker impedance too low?
    Hey...thanks for the tips man.

    Checked the speaker impedance and it is ok ( 8 ohms). Tha cable that connects the module to the speaker is ok too (no shorts). The fan operates correctly too.

    One thing I could not measure was the bias. Even using a similar schematic that i found here:

    https://elektrotanya.com/parsek_mark.../download.html

    There is no indication about, what Bias I should set the amp. I tried to measure the dc voltages in D3, D4, D5 and D6, but found a different value of the schematics. D5 is measuring 0,4V and D6 is -3,0. D3 is 0,3 and D4 is -2,9. Those 4 diodes are ok. No shorts or opened.

    How do I check the iddle current?

    Thanks again

  27. #97
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    I would measure the voltage across the 0.33 ohm resistors - 3.3mV would be 10mA and I suggest that is a reasonable number. These FETs are designed for switching applications and, to be frank, I really have no idea what a corrent bias current would be. I can say that if they run hot at idle, that that is too high. If you see a crossover notch when scoping the output then it's too low.

    The best way would be to use a distortion analyzer and gradually increase the bias, stop when you no longer get any rapid improvement in THD but taking care not to let it get too high.

    You're real problem might be a matching issue. These FETs come with a very wide +/-50% in gate threshold voltage and that could lead to significant variations in the current between them when operating. At full 500W into 4 ohms the peak source current in each FET is over 5A i.e the drop across each 0.33 ohm resistor is getting on for 2V and that will help to match the currents. At a full output into 4 ohms each FET will be dissipating something like 50W. That is a lot of heat to dispose of and any mismatch could make one much hotter than the next leading to failure.
    Last edited by nickb; 02-21-2017 at 10:05 PM.
    Experience is something you get, just after you really needed it.

  28. #98
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    Quote Originally Posted by Leooooh View Post
    It uses 3 IRFP240 and 3 IRFP9240. One IRFP240 and one IRFP9240 were shortened.
    You actually haven't specified how many MOSFETs you replaced. 2 or 6? Were they matched? As Nick says, matching MOSFETs in such amps is extremely important. Even if MOSFETs are from one production batch. Did you match them?

    Mark

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