Audiolab 8000S repair

Hi all,

This is my first post here. I wish to share my experience with my Audiolab 8000S integrated amp.

I recently bought it. I saw it advertised and read a few forum posts on both the 8000S and the earlier model 8000A. I didn't know it before, but realized it would be a fun project. The 8000S differs from the 8000A in that it is digitally relay controlled, lacks a phono input, and has a remote control. I downloaded the diagram before buying it as I knew there would be work to do. The seller informed that only the CD input was working and that the remote was missing. So far I'm very satisfied!

I'ved mated it to a pair of Acoustic Energy AE100 shelf speakers. It's a brilliant combination, I think. Instruments are clear, voices well located, and despite the diminutive size of the AE100's, there's plenty of bass to fill my basement room.

But now to the subject of this post, the two problems I have with the amp:

The input selector behaves strangely. As the seller had warned me, it only works with the CD input. Selecting another input works, for a few seconds, then the amp turns the selector back to CD. This is a motor driven input selector so the onboard microcomputer actually turns the selector. The diagram shows that the selector contains two switches: 1) A multipole switch which is fed to the microprocessor, which then activates and deactivates the appropriate relays. 2) A single pole switch which I'm not sure about but think tells the microprocessor that the multipole switch is at a valid selection or that it has been moved. I have posted a video of the problem on Flickr: Flickr

That's problem #1. Problem #2 is that eight resistors in the power amp section are completely discoloured from heat. These are normal 0.25W 3K resistors feeding 12V zeners directly from the 40V supply rail and even though they are run in parallel to form a combined 1K5 resistor, about 0.35W is dissipated in each of the eight - and they are very hot. This is a well known problem with these amps, both the 8000A and 8000S as discussed in other posts here. I'm suriprised the design has not been rectified in the 8000S.

I have attached a few photos of the subjects of my investigations.

I plan to unsolder the input selector and take it apart to see if it can be cleaned. The remote control is RC5 so it should be possible to find a replacement for the original which can even control my CD player. I am ordering new 1W resistors to replace the eight burnt resistors, but its obvious that the PCB will also need cleaning.

I plan to upgrade the PSU capacitors. They are ELNA 10000 uF/50V, but as the amp seems to be from 1997, they are probably well beyond their lifetime.


Any input or encouragement will be greatly appreciated! :D


Best,
Anders
Denmark
 

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The 4.7Uf (usually Elna RE3 IIRC) often goes out of tolerance and can cause issues. Replacing those often restores the original sound FME


There are 4.7uF caps as decoupling on the supply lines for each channel (marked yellow ing the cut out of the diagram). Do you mean those?


Raising the new resistors above the PCB will help also.


I have ordered 2W 1K5 resistors and will raise them well. Thanks!
 

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Hi all,

This is my first post here. I wish to share my experience with my Audiolab 8000S integrated amp.

I recently bought it. I saw it advertised and read a few forum posts on both the 8000S and the earlier model 8000A. I didn't know it before, but realized it would be a fun project. The 8000S differs from the 8000A in that it is digitally relay controlled, lacks a phono input, and has a remote control. I downloaded the diagram before buying it as I knew there would be work to do. The seller informed that only the CD input was working and that the remote was missing. So far I'm very satisfied!

I'ved mated it to a pair of Acoustic Energy AE100 shelf speakers. It's a brilliant combination, I think. Instruments are clear, voices well located, and despite the diminutive size of the AE100's, there's plenty of bass to fill my basement room.

But now to the subject of this post, the two problems I have with the amp:

The input selector behaves strangely. As the seller had warned me, it only works with the CD input. Selecting another input works, for a few seconds, then the amp turns the selector back to CD. This is a motor driven input selector so the onboard microcomputer actually turns the selector. The diagram shows that the selector contains two switches: 1) A multipole switch which is fed to the microprocessor, which then activates and deactivates the appropriate relays. 2) A single pole switch which I'm not sure about but think tells the microprocessor that the multipole switch is at a valid selection or that it has been moved. I have posted a video of the problem on Flickr: Flickr

That's problem #1. Problem #2 is that eight resistors in the power amp section are completely discoloured from heat. These are normal 0.25W 3K resistors feeding 12V zeners directly from the 40V supply rail and even though they are run in parallel to form a combined 1K5 resistor, about 0.35W is dissipated in each of the eight - and they are very hot. This is a well known problem with these amps, both the 8000A and 8000S as discussed in other posts here. I'm suriprised the design has not been rectified in the 8000S.

I have attached a few photos of the subjects of my investigations.

I plan to unsolder the input selector and take it apart to see if it can be cleaned. The remote control is RC5 so it should be possible to find a replacement for the original which can even control my CD player. I am ordering new 1W resistors to replace the eight burnt resistors, but its obvious that the PCB will also need cleaning.

I plan to upgrade the PSU capacitors. They are ELNA 10000 uF/50V, but as the amp seems to be from 1997, they are probably well beyond their lifetime.


Any input or encouragement will be greatly appreciated! :D


Best,
Anders
Denmark



Hi Anders
I came across a similar problem with the selector switch - please see my solution as the last post here: DIY Audio Projects Forum • Audiolab 8000S ALPS motorised source selector problem

FYI I had all the overheated resistors replaced in my amp by the audiocellar.com - as well as a rather ugly repair to the PCB involving soldering wires along the PCB tracks to make them more robust. All works well now
 
I can't understand why the designers of this amp didn't raise the resistors off the pcb knowing they will run hot. It takes alot of heat to discolor a fiberglass pcb and once it does that, the darkened area can become slightly conductive. Hopefully you will be able to desolder those resistors without what's left of the eyelets and traces crumbling on you. I would cut them out first and then unsolder whats left of the pins. That way you'll have the best chance of success. Just get some fresh solder into those eyelets before you remove the resistors.
 
Hi Anders
I came across a similar problem with the selector switch - please see my solution as the last post here: DIY Audio Projects Forum • Audiolab 8000S ALPS motorised source selector problem

FYI I had all the overheated resistors replaced in my amp by the audiocellar.com - as well as a rather ugly repair to the PCB involving soldering wires along the PCB tracks to make them more robust. All works well now


That's VERY interesting. I only just read your reply. I tried to remove the selector a few days ago, but couldn't get it out with my amateur desoldering tools so ended up resoldering it back in. I have not noticed the pins you point it, but after I fiddeled with it, the problem seems to have disappeared. I obviously need to recheck that! :)


I can't understand why the designers of this amp didn't raise the resistors off the pcb knowing they will run hot. It takes alot of heat to discolor a fiberglass pcb and once it does that, the darkened area can become slightly conductive. Hopefully you will be able to desolder those resistors without what's left of the eyelets and traces crumbling on you. I would cut them out first and then unsolder whats left of the pins. That way you'll have the best chance of success. Just get some fresh solder into those eyelets before you remove the resistors.


They were indeed *very* diffcult to remove, and I did unfortunately damage some of the traces. I removed six of the resistors but left in two and soldered the new resistors on top. I regret not doing that with all of them as the new resistors of course have larger diameter pins and were difficult to feed into the holes.


Each of these 0.25 watt resistors dissipates (40-12)2/3000 = more than 0.26 watts. What were the designers thinking :rolleyes:?

Best regards!


I have asked myself the same question! And it's worse in my amp as the resisters were in fact not 3K, but 2K. Mine is an issue 3 PCB.


I've measured 42V on the supply rails, so we have:



(42-12)2/2000 = 0.45W :eek:
 

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I wonder if the original design had these as 'thermal fuses' or whether it was just bad maths?


I have a theory that the amp was designed for a lower voltage PSU but someone in marketing ordered a higher voltage transformer to "up" the specs, and then when they realized the problem they merely increased the resistance of the resistors from 2K to 3K so that they would not exceed the specs too much... Also from a design philosophy point of view, I don't think these amps were designed to sound good before being reliable machines :D
 
Hi Anders
I came across a similar problem with the selector switch - please see my solution as the last post here: DIY Audio Projects Forum • Audiolab 8000S ALPS motorised source selector problem


So the selector switch has been behaving better since I worked on the amp last week, but especially on tuner it still misbehaves. That's the input I use for my Bluetooth DAC, so that's somewhat annoying :rolleyes:


Anyway, it looks like we have different PCB's and probably also different selector switches as mine doesn't have any pins where yours have. As mentioned earlier, mine is an Issue 3 PCB.



This has lead me to think that when you soldered the missing pins on your switch, perhaps you didn't actually solve the problem, but just messed enough with the switch to make it go away? I'm merely guessing.



A quick test seems to indicate that applying solder sort-of works. I soldered a couple of pins just now, and it seems better... :D



Anyway, I'm going to go back to my original plan to unsolder the switch, dismantle it, and try to clean it. I just need to get myself a real desoldering tool to do that job :cool:
 

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Succesful repai

I've been looking forward to making this post as I finally got to do the repairs I wanted :D

The 4.7Uf (usually Elna RE3 IIRC) often goes out of tolerance and can cause issues. Replacing those often restores the original sound FME

You were right, thanks! They had given up completely, at least my multimeter coulnd't measure any capacitance at all. I've replaced them with 105 °C rated ones, hopefully they will stand the hot environment in that area better. (I put in 10uF instead of 4.7. My vendor didn't have any 4.7's in stock with the 105 °C rating.)

I also finally managed to remove the selector switch. I looked at some professional unsoldering gear to get it out, but settled for a Velleman VTDESOL3 heated desoldering pump, and it did the job very well. Getting the switch out is not easy even when all pins are free as front panel keeps it in place even with the screws removed. I managed to wiggle it out (and in again) by loosening the nuts on the two other selectors and the volume pot. So what did I find once I got it out? :p

Well, first of all I found out how the switch works ;) It has two layered rotary swtiches: The back one is the selector, and the front one is a switch which is used by the motor drive to detect whether the switch is in a valid position or not. The motor drive does not have to overcome the clicking for manual selection, but drives the selector and the front part together. I recorded a little video showing it here: Flickr :cool:

Second, and this is the important part :rolleyes: I found that the grease from the motor drive apparantly had penetrated the copper tracks on the switches. There was also some corrosion. Perhaps the amp has been stored in a humid place, or the greas could have been there from the beginning? I cleaned off the grease and bent the contacts slightly forward, and reassembled the switch module. As I have no way of testing the switch, I soldered it back in wondering if my repair would be succesful :rolleyes: Fortunately it was, that this has fixed the original problem :king:

The amp will still mute when I touch the selector switch, but it holds all positions steady now. I'm still testing it leaving it powered on, but so far I haven't seen any misbehaviour. The remote control was lost when I got the amp, but now that it seems I have rescued the original functionality, I'm going to look for one. It should be a standard RC5, according to the manual.

Best,
Anders
 

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Hi.
I have the same integrated with the same problem as Anders.
Today I resoldered the resistors that gets warm. The old solder did not look good. I also tried to remove the input selector without success. I soldered it back, but now I get no sound from the left channel. Before I had the same problem as Anders here but otherwise it was working fine.
When I resoldered the resistors I accidently bridged two of the resistors with solder but I used a knife to scrape it off.
Could it be a broken resistor that causes this? What could have happened?
I have ordered some new resistors and will change them when I receive them.
I hope you can understand my english.
Thanks / Robert
 
Hi.
I have the same integrated with the same problem as Anders.
Today I resoldered the resistors that gets warm. The old solder did not look good. I also tried to remove the input selector without success. I soldered it back, but now I get no sound from the left channel. Before I had the same problem as Anders here but otherwise it was working fine.
When I resoldered the resistors I accidently bridged two of the resistors with solder but I used a knife to scrape it off.
Could it be a broken resistor that causes this? What could have happened?
I have ordered some new resistors and will change them when I receive them.
I hope you can understand my english.
Thanks / Robert
Yes, that input selector is quite difficult to remove. You need patience and care, and a good solder sucker as well as good desoldering wicks.

It's hard to say what has gone wrong with your left channel just from this, but since the input selector merely controls the PIC processor which in turn controls the various relays in the AMP, it's more likely the resistors that have caused your problem than the selector. Each group of overheating resistors feed a zener diode which in turn feeds regulated voltage to the input stage of the output amp. Most likely something has gone wrong in your soldering and there is no power. So I suggest you find your multimeter and check the voltages on either side of the resistors and zeners. It should be 12V across the zeners. See the attached screen shot from the service manual.

Best
Anders
 

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Good luck, but don't hope, rather you should really measure the voltages in the circuit before you start making any more fixes. Finding out where the problem is before trying to fix it is elementary and we're gifted here with a service manual with excellent troubleshooting guidance. Read that thoroughly to make sure you understand what you're doing :)