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HackerNap failed

Bemused

What's this all about then?
Really need your help now guys.

Vellerman speaker protection operated, 50V DC on HackerNap output.

Amp is currently discharging and I have to find my old build notes.

What do I check first?

Many thanks
Tony
 
Just measured the output transistors (MJW21194G) base is short circuit to collector and emitter, collector to emitter short, in fact its now a three terminal piece of wire.

Oh, perhaps I should mention that I measured with the transistors still in circuit.

Just tried RS but they don't do MJW21194G, Farnell do but I have to order six of them for nearly £30, ouch
I think I need to get four to be safe, I already have TR7 (MJE15030) & TR8 (MJE15031) as spares

Any other UK supply?

Tony
 
My fault, I didn't read your post properly.

Hopefully someone will come up with a bit of help, or can add your bits to a larger order.
 
Hi, Tony

I had a problem with my hackernap (self inflicted) and I have some MJE4281 in one now and I can't tell any difference.

I got them from Onsemi as samples you have the register amd make some stuff up about what you want them for but for about $20 they will senmd you some.

I have some used MJE3281s you could have for free.

Or if some one is ordering you could tag on to there order.


Pete
 
I would not just rush into replacing the output trannies without investigating why they failed. Did you short the outputs? If not then there could be a fault elsewhere that might repeat the expensive loss of those trannies!!
 
Sorry things have gone wrong Tony. Try "Future Electronics", they are usually well priced. Also measure the driver transistors cos they can go too. Good luck!
 
Hi, Tony

I had a problem with my hackernap (self inflicted) and I have some MJE4281 in one now and I can't tell any difference.

I got them from Onsemi as samples you have the register amd make some stuff up about what you want them for but for about $20 they will senmd you some.

I have some used MJE3281s you could have for free.

Or if some one is ordering you could tag on to there order.


Pete

Thanks Pete, a kind offer but I need to keep to both amps the same, its a sort of obsessive problem I have.

What I need to do is workout what else I may need in the future and make up the Farnell order that way, unless someone else needs to pigyback or visa versa as you say.

I was eager to get the amp fixed in order to hear the B4 so initially thought to get the output transistors on the way.

Had a good slug of wine now though and are chilling back down ;)

Tony
 
Try CPC.
They are part of the Farnell group and have many of the same parts, but interestingly often at lower prices and in lower quantities.
Henry
 
I would not just rush into replacing the output trannies without investigating why they failed. Did you short the outputs? If not then there could be a fault elsewhere that might repeat the expensive loss of those trannies!!

Thanks Jo
Yes I was rushing to get the transistors on there way but I would not fit them until the nice clever chaps helped me with some more detailed diagnosis.

I don't actually know when the amp failed, could have been any time over the last eight days since my last session.
I noticed the failure as a result of plugging in my newly built B4 http://www.pinkfishmedia.net/forum/showthread.php?t=118242

No shorts applied, just a power down (the amps are always powered up), swap interconnects then power back up.

Tony
 
Sorry things have gone wrong Tony. Try "Future Electronics", they are usually well priced. Also measure the driver transistors cos they can go too. Good luck!

Thanks, just checked Future, it a stock item but current stock is zero.
Yes there must be a lot to check before powering back up.
 
Hi, Tony

I have 8 uesd MJE3281s you can have.

Add some solder http://uk.farnell.com/multicomp/507-1082/solder-wire-60-40-1-2mm-250g/dp/5071082
I wouldn't mind some my self if you need to add something to make up the minimum order cost.

Pete

Well if you have enough for both amps it sounds better but then I would have to strip the other amp and they are a little tricky in my cases, again I need very long legs to reach the heat sink.

However the HackerNap is a great amp and its worth a lot more than £30, so I will order some new transistors, do the proper diagnosis and fix it proper.
Hey might even learn a little along the way.

Now to your solder, 1.2mm, not 0.75mm?
email me "tony at eclfirst dot co dot uk" I will pick up email in the morning.

Many thanks
Tony
 
Update

Board now removed which was quite tricky in my amp.

Output transistors removed and verified short circuit.

Output transistor Tr9's emitter resistor R26 holed and open circuit.

Tr7 driver looks ok

Tr8 driver is open circuit,
Tr8 base resistor R19 is open circuit (fried)
Tr8 collector resistor shows signs of burning

Looking like I should rebuild the whole output stage, would the main rail capacitors C13 + C14 have been damaged?

Tony
 
Hi, Tony

Something went big time on that amp!

Check Tr6 and D3 near Tr8

I would replace the drivers Tr7+8, do you have a variac to power it up slowly?

Email sent


Pete
 
Yes is went big time, although I heard nothing.
I originaly assumed it was the introduction of the B4 but not having listened for eight days it probably failed some time before.
The B4 looks fine, has hardly any dc on its output and there are output caps also.
The diode D3 measures ok but I am thinking to relace the whole stage to be safe.
I will look further into the amp over the next day or so.
Yes a variac is a good idea and I have one.

Thanks
Tony
 
I noticed the failure as a result of plugging in my newly built B4 http://www.pinkfishmedia.net/forum/showthread.php?t=118242

No shorts applied, just a power down (the amps are always powered up), swap interconnects then power back up.

Tony

Tony

Just a quick question - how discharged was the amp before you connected the B4 ? It is possible that there was sufficient energy left for the amp to go into oscillation when the inputs were swapped. Some amps (Crimson Elektrik for example) are prone to this - I speak from experience, in my case the Velleman did not save the speaker driver !
 


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