View Full Version : Just wondering if anyone here would be able to help with my audio lab 8000p ?
haimsadia
26-09-2010, 05:42
Okay, left channel is dead, i took out the output transistors and tested them. TO ME everything seems well...
Power is going into the board too so that rules out the PSU.
anyone keen to lend me a hand faultfinding it?
Cheers,
They have a glass fuse on the circiut board from what i remember, have you checked this? also i had a simular caimbridge mono block amp, it had a dry joint on the speaker output cusing no output
haimsadia
26-09-2010, 09:47
NO? i'm not able to find a glass fuse on the circuit board? or is it just my lack of experience that i'm limited by?
i dont think that there is a dry solder joint as the right channel heatsinks are hot and when you touch the left they are DEAD cold....
here is a photo of the PCB i took
http://img121.imageshack.us/img121/4614/img03291.jpg
They also have relay protection, but I can't remember if it was for both channels together or not..
I must add that I never got to see much of Audiolab's innards as they were incredibly reliable and on a trip to the factory, Shaun (Sean?) the engineer had an almost empty workshop, the returns were so low.
[edit] - I'd take a look around the relay which seems to be one per channel these days. Those white coated "resistors" could be fusible ones and one of these could have gone open circuit - just a thought...
haimsadia
26-09-2010, 09:57
hmmmm just tested most of them and all seem fine?
haimsadia
26-09-2010, 10:03
the pcb around '2SA1209S' in the middle PNP transistor seems discoloured/ browner than the right channel (which still works)
Reid Malenfant
26-09-2010, 13:34
the pcb around '2SA1209S' in the middle PNP transistor seems discoloured/ browner than the right channel (which still works)
Yes i noticed it looked as if something got hot :scratch:
Check the underside of the PCB around that TO126 transistor that is browning the board & look for dry joints. The fusible white resistors are no such thing, they are simply insulated links ;)
The relay is only operating the single channel, when you power up & after a few seconds does this relay click & attempt to connect the amp to the outside world?
If it doesn't it'll likely be due to a DC offset, a multimeter would be of some use here to find out if it's the case. Alternatively it's just about possible that the relay coil or the circuit controlling it has gone up the swanny :rolleyes:
Loads of possibilities, i'm sure we'll get there in the end :)
Sorry my mistake, i had the 8000m mono blocks for a while and not the 8000P
haimsadia
26-09-2010, 18:39
Hey thanks for the Help guys... I will check it up tonight when I come back from Uni!!!
haimsadia
27-09-2010, 08:16
Relay operating. i can see it moving inside and switching about 10 seconds after mains has been restored.
I'm letting the amp rest before i try and look at the solder joints etc as i'm not sure what will cap will still be charged up... :S
Reid Malenfant
27-09-2010, 14:42
Relay operating. i can see it moving inside and switching about 10 seconds after mains has been restored.
That sounds pretty normal then ;) You obviously don't have a DC offset problem or the relay wouldn't close :)
You say you checked some of the links earlier when they were mistaken for fusible resistors? How did you do this? Do you have a multimeter?
I'm hoping you do as i have a feeling that the amp is probably working ok & that there is a break or bad connection between the amps output & the speaker sockets. I may be wrong but it's looking that way to me :scratch: It could be on the input to that channel as well while i think about it.
haimsadia
28-09-2010, 09:45
hmmmm i let the mains stay on and after about one min BOTH relays switch off!
so now both channels arent operating.
i think that since the power transistors are working i will solder them back in.
any advice as to how to proceed?
Reid Malenfant
28-09-2010, 17:29
hmmmm i let the mains stay on and after about one min BOTH relays switch off!
so now both channels arent operating.
:eek: This is getting to be a bit of a pita :lol:
If both relays are dropping out at the same time after they happiliy closed then i'd take a look at the power supply or supplys if there is more than the normal +/- rails. There might be a seperate low voltage rail/s used to power the relay circuit & possibly the TLO op amp i think i saw on the PCB which probably adjusts the DC offset or is used in the relay control circuit :confused:
I wish i knew the amp or had a circuit diagram as i'd be able to help a lot more. As it is i'll see what i can track down on the net ;)
Reid Malenfant
28-09-2010, 17:56
Ok, i have found part of the amplifier circuit diagram :eyebrows:
The TLO op amp is indeed used to correct for DC offset as i figured. It's powered via +/- 12V supplys that are shunt regulated via a pair of zener diodes directly from the main +/- voltage rails.
The thing is i need the complete circuit for the whole amplifier because it's a bit of an oddity :lolsign: I can't see where the feedback loop is closed as all i can see are what look to be connectors. Another thing is that the feedback appears to be via two resistors & capacitors like it might be split. I can't see any reason why anyone would do this so i need to see the full diagram :doh:
This is what i have found so far (http://media.photobucket.com/image/audiolab+8000p+circuit+diagram/Trunky1812/8000diagram.jpg) :scratch: I'm sure anyone who understands electronic circuits will be puzzled by the two resistors & caps feeding the second transistor of the input long tailed pair :eyebrows:
Tbh it's not a bad looking circuit if only i could see the rest of it :eyebrows: There is quite a bit of room for improving the thing (if you ever wanted to) if we can get it running again ;)
haimsadia
28-09-2010, 19:37
hmmm yeah.... you seem to know alooot more than me. i'll check that opamp...
i wouldnt mind improving it :D and also yeah i'm dieing to get it working!
i'll do my best to find the rest of the diagram!
Reid Malenfant
28-09-2010, 19:47
The fact that both channels are messing about now suggests it's something common to them both ;) This might suggest the power supply, though without seeing the rest of the circuit which includes the relay & protection circuits we are at a bit of a standstill.
That is unless you have a multimeter? :scratch: Have you got a multimeter? Please let me know & we might be able to proceed a little further ;)
Apologies for the bold stuff but i have asked previously on possibly a few occasions & received no reply...
Apologies if I misinformed by accident earlier regarding the possibility of fusible resistors.
Do Audiolab still have the great service dept they used to have? In the Tag days, it became a fully costed enterprise, with evry "15 minute unit" costed out. I was hoping that things may not be so mercenary now. if this is the case, why not let their service dept fix it properly?
That's a fairly unorthodox push-pull circuit and not at all easy to read. I think (c) is the overall NFB back to the op-amp from the output pair and I can see the Zobel network. Where the hell do (d) and (e) go from those resistor/capacitor pairs? There's just a connector on the r/h side :scratch:
I'd check that the 22R resistors feeding the small signal stage +/- rails haven't burned out. Also that the protection trannies on far right aren't kicking in as soon as power is applied.
Try isolating one channel at a time to see what is bringing down the rails or inducing relay protection?
haimsadia
28-09-2010, 23:08
The fact that both channels are messing about now suggests it's something common to them both ;) This might suggest the power supply, though without seeing the rest of the circuit which includes the relay & protection circuits we are at a bit of a standstill.
That is unless you have a multimeter? :scratch: Have you got a multimeter? Please let me know & we might be able to proceed a little further ;)
Apologies for the bold stuff but i have asked previously on possibly a few occasions & received no reply...
Dont appologise haha... it's okay... i normally use my iphone to read so MIGHT lose some key question!!
yes i have a DMM! i also have an oscilloscope so those measuring instruments are of no problem if they are needed!
Apologies if I misinformed by accident earlier regarding the possibility of fusible resistors.
Do Audiolab still have the great service dept they used to have? In the Tag days, it became a fully costed enterprise, with evry "15 minute unit" costed out. I was hoping that things may not be so mercenary now. if this is the case, why not let their service dept fix it properly?
hmm i want to fix it myself so probably unless i've explored EVERY possible avenue then that's when i'll seek advice/help from a pro.
being a student i want to learn so this is the perfect thing for me!
That's a fairly unorthodox push-pull circuit and not at all easy to read. I think (c) is the overall NFB back to the op-amp from the output pair and I can see the Zobel network. Where the hell do (d) and (e) go from those resistor/capacitor pairs? There's just a connector on the r/h side :scratch:
I'd check that the 22R resistors feeding the small signal stage +/- rails haven't burned out. Also that the protection trannies on far right aren't kicking in as soon as power is applied.
Try isolating one channel at a time to see what is bringing down the rails or inducing relay protection?
how should i check if the protection trannies arent kicking in? desolder them and check them out like i did with the power transistors?
and and yes, i will also check the resistors tonight!
how should i check if the protection trannies arent kicking in? desolder them and check them out like i did with the power transistors?
Yes, try testing each tranny out of circuit. To be honest, the fact that your output trannies are ok and both channels are not working seems to point to the power supply or master protection circuit being at fault. How do the +ve and -ve rails measure?
haimsadia
29-09-2010, 19:53
Wasn't able to get it done last night, will be on onto it tomorrow in the weekend!
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