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QUDOS - the brilliant new amplifier boards from Avondale

Boy am I feeling frustrated. New I should have stopped when feeling tired.
I connected the second board up last night and switched on with the light bulb in place to find that there was no current reading on the DMM and high voltage offset.
Switched off and checked things only to realise that I had plugged the MM leads into the correct sockets but had set the dial to the mv setting not the ma one.
Any pointers as to what components I will have zapped much appreciated.
 
No magic smoke. I've been rereading the thread I started last year so will follow your advice and a few others from that thread. Seem to have a memory like a sieve at the moment.
There was somewhat more voltage on the output this time. And I had so been looking forward in listening to stereo today.
 
Marra said:
Boy am I feeling frustrated. New I should have stopped when feeling tired.
I connected the second board up last night and switched on with the light bulb in place to find that there was no current reading on the DMM and high voltage offset.
Switched off and checked things only to realise that I had plugged the MM leads into the correct sockets but had set the dial to the mv setting not the ma one.
Any pointers as to what components I will have zapped much appreciated.
Click to expand...

You have the MM connected into the +ive rail on mVs? The MM should be a very high resistance when measuring voltage. So should have restricted the supply current.

Have you measured again but with mA? What current did you measure if you did?

When you say a lot more voltage on the output how much more? I seem to remember reading that if the speaker output was at supply voltage then output transistor were popped.
 
@ chiily yes I checked with the mm on the mA setting but it did not show any reading no matter which way I turned the trimmer. The offset was at 24V and the light bulb limiter was glowing.

Hopefully get a chance to unsolder the transistors today and check them with the Atlas tester.
 
Marra said:
@ chiily yes I checked with the mm on the mA setting but it did not show any reading no matter which way I turned the trimmer. The offset was at 24V and the light bulb limiter was glowing.

Hopefully get a chance to unsolder the transistors today and check them with the Atlas tester.
Click to expand...

Also check the diodes or just replace them (D3&4 I think) across the outputs...I recall having similar and after removing the transistors they tested OK, it was one of these diodes blown. I replaced both transistors 'just in case' they had taken a bit of abuse. Ive had it where after a bit of this abuse they measure OK on the Atlas out of circuit but when back in circuit there was still an issue.
 
I have just desoldered the driver and output transistors all of which measure exactly hfe wise as before as does the trimmer. The diodes also measure correctly.

Puzzling.
 
Swap them, the low voltage used in the tester might make them read o/k.

You did check the right channel, didn't you?

Its the sort of mistake I am capable of!

Pete
 
Ok will do. Have to place an order with Farnell as I am out of the driver transistors.

Oh yes the good one is boxed up. I use a different p/s for testing.
 
laverda said:
The bias will be OK at 100mv when strapped to a proper sink...My mono cases run at 26deg/c at 100mv bias
Click to expand...

How can you have such low temperatures?

I run two ncc220 at 110mA bias in a nap140 case and I measure ~36 deg/C and the others in a 250 case (with HRC200) at around 42 deg/Celsius with a not so precise IR gun.
The case was warm with NCC200 running at 36mA bias, and near hot as now running at ~50-60ma (don't remember)
 
mirkov said:
How can you have such low temperatures?

I run two ncc220 at 110mA bias in a nap140 case and I measure ~36 deg/C and the others in a 250 case (with HRC200) at around 42 deg/Celsius with a not so precise IR gun.
The case was warm with NCC200 running at 36mA bias, and near hot as now running at ~50-60ma (don't remember)
Click to expand...

Your quite right mirkov, I stand corrected. I have just taken readings again with the gun and the case temp is 35 deg/C for the two monos. The temp at the fins on the NCC220 voyager below is 29 deg/C and thats running 150ma at the output and 24ma at the front end (IIFC) so +170ma in total. Thats after days of 24/7 running. My first readings must of been after only a few hours....

40259610181_deaf8e6fa4_h.jpg
 
Having waited patiently for two weeks for my Farnell order to arrive; UPS having lost the original package I set to and replaced the driver and output transistors and the diodes. I did the test point check first before replacing things and was able to set the voltage to 1.65vdc. Unfortunately the same thing happened as previously despite my having the dmm set correctly this time. On the 300ma setting I get an overload reading and the light bulb glows. Some hand holding/ advice much appreciated
 
Marra said:
Having waited patiently for two weeks for my Farnell order to arrive; UPS having lost the original package I set to and replaced the driver and output transistors and the diodes. I did the test point check first before replacing things and was able to set the voltage to 1.65vdc. Unfortunately the same thing happened as previously despite my having the dmm set correctly this time. On the 300ma setting I get an overload reading and the light bulb glows. Some hand holding/ advice much appreciated
Click to expand...

OK, replace all the other transistors ...I know its a pain but they may 'all' check out OK on a tester off the board but one or more may not now like the full rail voltage...I recall something similar and spent what seemed a life time whipping one transistor out at time and testing ....They all tested OK. But I still had 18v on the output. I phoned a commercial electronic engineer friend ....His advice, it will be quicker to 'replace the 'firkin things' if you can't find the wobbly one....Looking back, I'm sure TR4 ZTX753 was at fault as it was running far to hot...but measured OK. off board.

Someone might be along soon and advise on a more 'elegant' solution.
 
Before ripping out all the transistors you should check that all the components are correct and there are no dry joints/solder bridges. From your post it sounds like this board had never been powered up before, so the malfunction may be completely unrelated to the DMM. (If you have a second meter you could investigate what happens to the resistance between the current measurement terminals of the DMM when the mv setting is selected).
 
I had a similar high DC offset before and it was TR1 which was faulty
If you have a good board and a bad one you can compare readings between the 2
I would start with no power to each board and check all transistors and diodes with a diode tester
Then check all resistors on ohms
Check all capacitors
With all components being in circuit you will net get exact resistance and capacitance values but the should be similar between the 2 boards

Alan
 
Thanks guys I will check this afternoon. The board was cleaned then checked with a magnifying glass before connecting up so no solder bridges but will check again.
 
After Alan's "dode" tests and if you can power the board up wihout frying something:
1) check with a finger if any components are getting very hot (except the ZTXs whcih run hot anyway (if it's anything like an NCC200))
2) measure the Vbe of every transistor

This usually gives some good clues as to where the probem is.
 
Thanks Alan I will have a read.

This afternoon I recleaned the board and checked with a magnifying glass. All appears well; no solder links and the joints all look good. The resistance check between boards was also ok although I thought that I had found the problem when one reading was way out. Turned out to be my having turned the trimmer fully clockwise. When turned I was able to reach the same reading as the good board. I reconnected to the psu with the dmm and bulb tester in place. The bulb glowed more when turning the trimmer anti clockwise and there was 0.8V on the output.??
 
Marra
Its always best set the trimmer to the 50% point before fitting
If you can adjust it to get the same reading as the other board the the trimmer its self should be OK
During the Hackernap builds there were several people found dodgy trimmers and had to replace them
0.8v at the output could just be a leaky feed back cap or a large imbalance between TR1 & TR2 LTP

Alan
 
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