So where to begin...
Got this 3225PE free after it was damaged in transit and decided that it was worth saving but starting to having second thoughts now.
Long story made short, fixed the original fault (R437/R453/Q409/Q411/Q413/Q415/Q417 and Q401).
After setting idle current and offset (in both channels) and everything running sweet I power it down and proceeded to solder the 2 bridges that short the 1 Ohm resistors ( R455/R456 ) I had a very small spark on the Right channel R546 - 1 ohm resistor and after powering up I had 28Vdc on the output again ( original fault on the left channel)
After many checks found the new MJ2955 shorted but nothing else ( I checked every single active and passive component on that channel) and by checking I mean out of the circuit board.
So I powered it up again with in line light bulb protection and it worked but when I try to set up idle current for that channel I get over 30Vdc on the 1 Ohm resistor instead of the 25/30mV but output offset is normal at around 30mV
My problem is that I can't find any defective component, can't adjust idle current and I'm running out of talent...
Help please.
Got this 3225PE free after it was damaged in transit and decided that it was worth saving but starting to having second thoughts now.
Long story made short, fixed the original fault (R437/R453/Q409/Q411/Q413/Q415/Q417 and Q401).
After setting idle current and offset (in both channels) and everything running sweet I power it down and proceeded to solder the 2 bridges that short the 1 Ohm resistors ( R455/R456 ) I had a very small spark on the Right channel R546 - 1 ohm resistor and after powering up I had 28Vdc on the output again ( original fault on the left channel)
After many checks found the new MJ2955 shorted but nothing else ( I checked every single active and passive component on that channel) and by checking I mean out of the circuit board.
So I powered it up again with in line light bulb protection and it worked but when I try to set up idle current for that channel I get over 30Vdc on the 1 Ohm resistor instead of the 25/30mV but output offset is normal at around 30mV
My problem is that I can't find any defective component, can't adjust idle current and I'm running out of talent...
Help please.
So there can't actually 30V across a 1 ohm resistor, as that would mean 900W of generated heat.
Try measuring directly across the body of the resistor on the leads themselves--- avoiding probing on board traces which might be more convevient. If you still observe 30V, the resistor itself must be defective. If the reading is more reasonable, perhaps even 0V, then there's likely an open joint or broken PCB trace. Probe with one meter lead still on the resistor lead to locate.
Good luck!
Try measuring directly across the body of the resistor on the leads themselves--- avoiding probing on board traces which might be more convevient. If you still observe 30V, the resistor itself must be defective. If the reading is more reasonable, perhaps even 0V, then there's likely an open joint or broken PCB trace. Probe with one meter lead still on the resistor lead to locate.
Good luck!
Actually I think I just found the problem the 1 Ohm resistor reads 3.4 Mohms
Just going to get that resistor and report back
Just going to get that resistor and report back
And the winner is... The 1 Ohm resistor
I shorted the copper track under it, it's one of the "funny" things in the service manual, you remove the solder bridge to set up the idle current after repair but have to solder it back once it's done.
I know I should have waited for the capacitors to drain (no bleed resistors) before doing them.
Another thing is why you never have the resistor value you need in your (our) parts bin ?
Anyway found 1 and it's up and running just waiting a bit to solder the bridge back.
Lesson for the day don't keep working once you so tired that you can hardly stand on your legs
Thanks guys
I shorted the copper track under it, it's one of the "funny" things in the service manual, you remove the solder bridge to set up the idle current after repair but have to solder it back once it's done.
I know I should have waited for the capacitors to drain (no bleed resistors) before doing them.
Another thing is why you never have the resistor value you need in your (our) parts bin ?
Anyway found 1 and it's up and running just waiting a bit to solder the bridge back.
Lesson for the day don't keep working once you so tired that you can hardly stand on your legs
Thanks guys
Small update
After setting idle and offset I decided to give it a test run
Test speakers connected, inline bulb removed and power on.
Small oscillation through the speaker( right channel ) and less then 10 seconds later the magic smoke came out.
Back to the drawing board
After setting idle and offset I decided to give it a test run
Test speakers connected, inline bulb removed and power on.
Small oscillation through the speaker( right channel ) and less then 10 seconds later the magic smoke came out.
Back to the drawing board
The "power envelope" from Nad requires real skills on this schematic, it can work very well at low volume but release the magic smoke as soon as you ask for more ... and vice versa (even if it's rarer) wait that Molly passes by and that he has time, he knows them really well.
In this case the fault is on the output stage (2SD669/2SB649 and 2N3055/MJ2955) and even been careful in sourcing the transistor I got counterfeited parts (the power transistors).
Does anybody know or can suggest replacements from actual production ?
Or does someone have a stash of old stock original Motorola and Hitachi pairs that can sell and post ?
The classic poorly documented hometaxial to epitaxial issue. Try https://www.diyaudio.com/community/threads/nad-7020e.364825/post-6457510 and https://www.diyaudio.com/community/threads/nad-7020i-sudden-death.363517/post-6494954. Hope it helps.
Thanks for the link very good information.
I haven't checked the amp again but from what I can see R453 (180 Ohms) is burned again so...
I haven't checked the amp again but from what I can see R453 (180 Ohms) is burned again so...
If both N and P were Motorola, then they were not hometaxial. Only RCA made those, but several sources made equivalents. Older epi types were often thermally stable without the emitter resistors, but not always. With modern outputs, add 10 ohms base stopper resistors or 0.2 ohm emitter resistors. It is claimed that this messes up the “magic sound”of the original circuit but it won’t go into run away. But then any modern MJ15xxx or 2119x parts may be used. If something is causing instant death, there is another problem to fix first.
Any information and suggestions are welcome unfortunately in this case I was supplied fake transistors, I suppose it is the joy of online purchases even from a well known supplier (email with complaint sent) and no no Ebay items.
Does anyone ever heard of CDIL brand transistors ?
1st picture is from one (fake) but working 3055 after rubbing some propanol on the markings
2nd the look inside picture, does it look like a 115W die ?
Does anyone ever heard of CDIL brand transistors ?
1st picture is from one (fake) but working 3055 after rubbing some propanol on the markings
2nd the look inside picture, does it look like a 115W die ?
Attachments
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https://www.cdil.com/
Rupees 40 for CDIL, 45 for ST make 3055, some time back, they are reputed.
Roughly 50 US cents.
Site has TO-220, not TO-3.
So yours are NOS, or fakes.
Rupees 40 for CDIL, 45 for ST make 3055, some time back, they are reputed.
Roughly 50 US cents.
Site has TO-220, not TO-3.
So yours are NOS, or fakes.
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The one in the pictures was as ST branded one (fake)
I asked about CDIL because Switch Electronics is selling them at £1.92 each.
I asked about CDIL because Switch Electronics is selling them at £1.92 each.
If you can, get those.
But American poster 'indianajo' says there are better MJ series transistors, which can be used instead.
The shipping and handling adds up, CDIL is a long standing company, see their web site.
Should not be a problem, and nobody bothers to fake those....and good TO-3 are hard to get now.
Even 'BEL' made ones are sometimes fake, it is a government company, silicon to final product, which is defense stuff of excellent quality, and supplies to the civilian market are mostly devices which are below testing requirements, in other words tolerable rejects.
Price tends to be well in excess of market, so half price stuff is automatically suspect. Their 2N3055HV is famous, High Voltage grade.
CDIL has no such problems.
But find the fault first.
But American poster 'indianajo' says there are better MJ series transistors, which can be used instead.
The shipping and handling adds up, CDIL is a long standing company, see their web site.
Should not be a problem, and nobody bothers to fake those....and good TO-3 are hard to get now.
Even 'BEL' made ones are sometimes fake, it is a government company, silicon to final product, which is defense stuff of excellent quality, and supplies to the civilian market are mostly devices which are below testing requirements, in other words tolerable rejects.
Price tends to be well in excess of market, so half price stuff is automatically suspect. Their 2N3055HV is famous, High Voltage grade.
CDIL has no such problems.
But find the fault first.
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Getting ready for second round, parts on there way.
Going to run with the suggestion on another post and fit 4 resistor with the new set(s) of 3055/2955 but have to get 0.51 or 0.56 Ohms (have to buy) or go with 0.33 or 0.47 that I have in stock.
Recommendations ?
Going to run with the suggestion on another post and fit 4 resistor with the new set(s) of 3055/2955 but have to get 0.51 or 0.56 Ohms (have to buy) or go with 0.33 or 0.47 that I have in stock.
Recommendations ?
