Hi, you can use the grease but you do need the pads if using a single heatsink for all transistors.
Using grease or not will depend on the pad type
I use mica pad, so grease is necessary.
In my case, I apply grease on the transistors and in the heatsink, thus on both sides of the mica pad.
Center power transistor pin is most of times the collector (bipolar) or the drain (mosfet) and must be isolated from heatsinks and from other complementary transistors in general.
If your heatsink is isolated from ground (chassis) and you only have the NPN/N or PNP/P transistors in parallel attached to this heatsink, then you don't need isolation. Heatsink will be "hot" connected to +V or -V thus having a voltage on it. You would need 2 heatsinks, one for NPN or N and another for PNP or P.
This is not your case, where we can see both complementary transistors pack (N and P) in the same heatsink as well as the small bias transistor. And heatsink looks not preparated to be isolated from ground/chassis.
Before powering up again, check this isolation first - sometimes small pieces of metal stick in between and when you tighten, it perfurates the pad and makes contact. And use the bulb or a resistor to limit the mains current.
Full pack cased devices dont need insulators but these are fully encapsulated in plastic. If you have a metal tab, you absolutely need insulator.
Not using insulation between the power transistors and the heatsink is foolhardy.
You should always use insulation. There's mica insulation (traditional) and specific insulation that doesn't require conductive thermal paste. When using mica, it's highly advisable to use thermal paste.
I always use specific insulation; these are silicone sheets that, in addition to providing electrical insulation, are also thermally conductive.
But in both cases, there must always be electrical insulation between the transistors and the heatsink. If you didn't insulate this, you'll have at least a short to ground and possibly a short between the power rails.
But in both cases, there must always be electrical insulation between the transistors and the heatsink. If you didn't insulate this, you'll have at least a short to ground and possibly a short between the power rails.
You should always use insulation. There's mica insulation (traditional) and specific insulation that doesn't require conductive thermal paste. When using mica, it's highly advisable to use thermal paste.
I always use specific insulation; these are silicone sheets that, in addition to providing electrical insulation, are also thermally conductive.
But in both cases, there must always be electrical insulation between the transistors and the heatsink. If you didn't insulate this, you'll have at least a short to ground and possibly a short between the power rails.
But in both cases, there must always be electrical insulation between the transistors and the heatsink. If you didn't insulate this, you'll have at least a short to ground and possibly a short between the power rails.
I'm not familiar with any audio power transistors that have a completely plastic casing. They always have a metal part in the back that's normally connected to the center pin of the transistor.
There are many transistors with completely plastic casings (without metal parts) but they come in smaller sizes. These don't require electrical insulation, as the colleague mentioned in the previous post.
There are many transistors with completely plastic casings (without metal parts) but they come in smaller sizes. These don't require electrical insulation, as the colleague mentioned in the previous post.
Brow you did a fopar.addmit it and move on. Diy audio lesson hopefully learnt. You only get better by learning from your errors.
This.
With the ease of use and quality available these days, I use silicon pad insulators.
No more messing around with grease as the pads are already impregnated with a grease.
always make sure the heatsink is clean with no bits that can poke through the insulator.
always make sure the transistor is clean with no bits that can poke through the insulator.
use a multimeter on the 'ohms' scale to make sure their is no electrical connection between the heatsink and transistors.
I also agree your grease looks far to grey to be 'normal' electronics silicon grease which is normally white. I suspect its a 'computer' style grease that has some metallic component in it.
Was there no assembly guide with the modules ??
Thank you for the help everyone! For the next time I will definitely be using thermal pads. My question now is could there be any other components that were damaged because of this? Considering this means the chassis was receiving a voltage from the amplifier would this mean that my power supply is damaged as it is connected to the chassis or will the earth wire to chassis have protected it? Could the soft start be damaged?
You had a full short circuit of some or even all transistors bodies to heatsink. If you want to learn what has possibly happened you could make a drawing with the short circuits in it to see where current was running. It got damaged big time which is a pity but you learn from it.
No one can make you more clever by reaching out. What you can do to avoid such risks is checking your work and the manual more than once before switching stuff on. When starting the hobby one better keeps exactly to what is written and better not have an own interpretation.
Please note the pads to be for both electrical insulation and heat transfer. The thermal "grease" is only to fill air pockets/uneven surfaces for better heat transfer but offers of course no electrical insulation. Normally the heatsink is not used as an electrical conductor but in this case it was 🙂
* If the heatsink is connected to the casing and the casing is connected to PE (randaarde) and the GND of the circuits are also connected to PE then you had possibly more than 1 short-circuit to GND/PE and destructive currents. I would disconnect the amplifier boards from PSU wiring and test the PSU to see if it still works. Its rectifiers have had a pretty hard time. If unsure you could use a lower voltage transformer like a 2 x 12V for that. The question you could ask yourself is why the soft start board would be damaged.
No one can make you more clever by reaching out. What you can do to avoid such risks is checking your work and the manual more than once before switching stuff on. When starting the hobby one better keeps exactly to what is written and better not have an own interpretation.
Please note the pads to be for both electrical insulation and heat transfer. The thermal "grease" is only to fill air pockets/uneven surfaces for better heat transfer but offers of course no electrical insulation. Normally the heatsink is not used as an electrical conductor but in this case it was 🙂
* If the heatsink is connected to the casing and the casing is connected to PE (randaarde) and the GND of the circuits are also connected to PE then you had possibly more than 1 short-circuit to GND/PE and destructive currents. I would disconnect the amplifier boards from PSU wiring and test the PSU to see if it still works. Its rectifiers have had a pretty hard time. If unsure you could use a lower voltage transformer like a 2 x 12V for that. The question you could ask yourself is why the soft start board would be damaged.
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the million dollar question.
what else may have been executed 😀
If you dont have a multimeter and know how to use it.
buy a new kit.
otherwise you could be chasing you tail swapping out part after part for a very long time.
having said that.
its already damaged, so feel free to use this as a learning experience.
what else may have been executed 😀
If you dont have a multimeter and know how to use it.
buy a new kit.
otherwise you could be chasing you tail swapping out part after part for a very long time.
having said that.
its already damaged, so feel free to use this as a learning experience.
Now you know what happens when a amplifier is fully shorted.
The bright side is no fires or eye damage from explosion.
Before any amplifier startup with mica insulators installed
Still use a volt meter / continuity test to confirm no shorts too the heatsink before power up.
Im sure in future it will be a funny story, not the very loud bad words said on power up.
The bright side is no fires or eye damage from explosion.
Before any amplifier startup with mica insulators installed
Still use a volt meter / continuity test to confirm no shorts too the heatsink before power up.
Im sure in future it will be a funny story, not the very loud bad words said on power up.
When I power it on with the amplifiers removed it the power supply still outputs +-55V as intended, so all is good?
You were lucky it seems but still measure rectifier diodes individually (write down results!) or simply replace them as a precaution. These have endured extreme currents and one better not trusts diodes that have been hit hard in the face. You can gamble but suppose one of the diodes* will be a short circuit itself in a few months time (their standard modus operandi) and what the consequences can be.
* Weigh the price of new rectifiers against the damage they may cause when leaving them where they are. Just 4 x FCU2040A will not be a showstopper. But ... these tolerate 120A surge currents and are used in parallel so maybe they survived perfectly. Up to you. If the PCB gets damaged by removing them you haven't gained anything.
You could leave them powered on for a day and check later on. Then decide. Edit out of importance: I take you did use the right fuses and they blew instantly didn't they?
Best thing is probably to replace the complete L15 boards as the costs of one new pair (75 Euro) outweigh repair.
* Weigh the price of new rectifiers against the damage they may cause when leaving them where they are. Just 4 x FCU2040A will not be a showstopper. But ... these tolerate 120A surge currents and are used in parallel so maybe they survived perfectly. Up to you. If the PCB gets damaged by removing them you haven't gained anything.
You could leave them powered on for a day and check later on. Then decide. Edit out of importance: I take you did use the right fuses and they blew instantly didn't they?
Best thing is probably to replace the complete L15 boards as the costs of one new pair (75 Euro) outweigh repair.
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I’m looking to replace the diodes it says N 8C FCU20A40 on them but online I can only find N 6C FCU20A40. Does this make any difference? It seems that FCU20A40 is the model name but I can’t find anywhere what the 8C refers to
This the amp? has enough outputs for 55 +/_ not sure about the drivers.
Dont see protection zener for mosfets.
This might ring a bell, was this the one that blows drivers when working?
wealth of 2N5551 / 5401 for drivers with reversed pin out when people tried to replace them?
dont look like much just outputs and a bunch of TO-92 transistors for replacement.
I Forget the package number check other threads, pins might be reversed.
Could be a can of worms to repair the boards you already have.
Or simple to just shotgun repair as they say, replace all semi conductors.
As mentioned again I think when the drivers blow you have to use reversed pin 2n5551/5401
dont hold me to that, does look familiar though
Yes I’m planning to just get new L15 boards. If I test the system like you say and leave them powered in for a day what is it I’m looking for? Am I just checking that the voltage at the output of power supply is still 55v or is there something else to look out for?
Thanks for the help I think I will just replace the amplifier boards but yes this is the model
I did not have any fuses between amp and power supply but turned off the amp immediately. The fuse on the IEC did blow.
I won't say a thing but be assured your reflexes are not as fast as fuses for testing. The light bulb tester would have saved your device too. Measuring continuity between transistors and heatsink before switching... ah forget it as it won't solve matters now.
It helps to be specific on a technical forum when you need specific help for a specific problem caused by a specific action by a specific person: you. If that x Ampère mains fuse was over rated (an unforgivable user error) you better replace all diodes in the PSU.
De kunst van het heel houden is de stroom te beperken.
It helps to be specific on a technical forum when you need specific help for a specific problem caused by a specific action by a specific person: you. If that x Ampère mains fuse was over rated (an unforgivable user error) you better replace all diodes in the PSU.
De kunst van het heel houden is de stroom te beperken.
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Sorry, for being unclear. The iec fuse was 10 ampere slow blow fuse. Maybe also good information to know that the 10 A circuit breaker in my house also went off.
If I run the amp for a day or so and check that the power supply is behaving stably would it be safe to put a new set of amplifiers on the end? What does it entail if the diodes short circuit will this cause the amplifiers to blow again? Would this be prevented with inline 4A fuses between the power supply and amp?
Obviously it must be difficult for you to know all the answers but I just want to learn what is good practice as I’ve definitely underestimated this. If I have to buy everything new again then I that’s what I’ll do to make sure I don’t end up wasting more money but of course I wouldn’t like to spend money unnecessarily either.
Thanks again for the help it is invaluable
If I run the amp for a day or so and check that the power supply is behaving stably would it be safe to put a new set of amplifiers on the end? What does it entail if the diodes short circuit will this cause the amplifiers to blow again? Would this be prevented with inline 4A fuses between the power supply and amp?
Obviously it must be difficult for you to know all the answers but I just want to learn what is good practice as I’ve definitely underestimated this. If I have to buy everything new again then I that’s what I’ll do to make sure I don’t end up wasting more money but of course I wouldn’t like to spend money unnecessarily either.
Thanks again for the help it is invaluable