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Old 3rd September 2009, 08:05 PM   #1
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Join Date: Sep 2009
Default Beginner amp repair project

Hi all

I've got some problems with my two 15 year old amplifiers and I thought this could be a fun opportunity to learn electronics and how to fix them.

The amplifiers and problems are...
Amplifier 1: Audiolab 8000a (My intended first project since the other is in use)
issue 1: input connectors have broken on 2 of the line ins,
issue 2: no sound coming from one channel.

Amplifier 2: Musical Fidelity - Tempest
Issue 1: sound occasionally cuts out on the left channel, changing the input channel to sit half way between sources can help for a few minutes/days.

I'm guessing what I need to learn to start with is
1 - how to diagnose the problems and how they relate to the various parts of the board.
2 - any precautions I need to take so I dont electrocute myself
3 - circuit diagrams for the amps
4 - advice on cheap essential kit I can buy in the UK
5 - multimeters ... how and where to use them and what the numbers mean?
6 - Soldering irons + related kit ... any videos/ tutorials on how to use them? Any advice on how to practice before jumping into the amp?
7 - any pre-requisite knowledge on electronic components
8 - Any advice on any general servicing that may be required after 15 years of constant use.

The limit of my electronics expertise to date has been building pc's and changing plugs so I know I have a lot to learn, but any advice on where to start and anything else you can think of would be greatly appreciated.

Thanks
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Old 4th September 2009, 01:06 PM   #2
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Join Date: Aug 2009
Location: West Midlands
Hi and welcome to the forum. I am new here too but i do have a little experience with amps as i am a keen modifier - my pet project being my beloved Pioneer A400.
With the Audiolab, when you say 2 of the input connectors are broken do you mean they dont work (ie. no sound when using them) or can you see they are physically broken?
also, with regard to the 8000a, when you say there is no sound coming from one channel i take that to mean regardless of which input you are using?
here are some suggestions for you to try:
1. check the underside of the PCB (printed circuit board) for dry or damaged solders - especially around where the inputs are connected.
2. swap the speakers over to make sure its not your speakers
3. try a different source to make sure it isnt the source
4. with regards to your Tempest does this problem happen with only one input or all of them? if its all then i suspect your input selector is on the blink
let me know how you get on as i may be able to offer more advice.
hopefully some of the more experienced people on here will also be able to guide you.
goodluck
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Old 4th September 2009, 04:39 PM   #3
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Location: Athens GREECE
a repair to an amplifier like that can be tricky

you need expirience to perform it and then instruments to verify the "size " of your upgrade or mistakes

i ma not trying to turm you down but the list you originally placed in your post is what all this forum is about .... none of us was born with this expirience and most of us may spend a full life time and never be able to complete the task ( comelete i cant really define )

what i would do :
----buy a vintage amplifier from a scrap yard that bearly works ( dont have to be big 40+40w will be tops

---- make a scedjule of what you need to upgrade that one ( knowledge,software,harware)

---- get your self some instruments ....dont really need to be state of the art neither expensive ( even a pc based osciloscope free from the internet is a good start )

work with this amplifier to make something to get expirience .... then see how far you go and then decide if you wana play with something more expensive ....

another good start will be to read the link above which is written in plain greek .... if you can understand afew things from there that is also a start

there you go
vintage amplifier repair/upgrade manual
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SERVICE ΕΝΙΣΧΥΤΩΝ ΚΑΙ ΙΑΠΩΝΙΚΩΝ ΜΗΧΑΝΗΜΑΤΩΝ ΗΧΟΥ www.eastelectronics.gr
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Old 5th September 2009, 07:48 AM   #4
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Hi and thanks for the responses.

@ifitsoundsgoodlistentoit
By the sounds of it - you are where I want to be... tinkering/upgrading your beloved amp!
To clarify... broken inputs mean a hole in the back of the chassis where the input connector has disintegrated with some parts now rattling around inside of the amp
The affected points are the left channels of CD, Tuner and Video In

This leaves ony 2 input channels (excluding phono), Tape 1 and Tape 2.

With regards to your numbered points...
1 - Unfortunately at this stage I wouldnt know how to identify a dry or damaged solder from a working solder.
2 - Its the right channel on each amp that cuts out. changing the speaker connects to the right channel affects that speaker only.
3 - Am experimenting with different sources/interconnects. Will update later
4 - Its all input channels that are affected - and have been for several years.


@sakis
yassoo tea kanis!
Sorry for the greek-glish but I've forgotten how to read/write greek.

Sound advice - I am completely clueless and without any tools - including a screwdriver that can open the audiolab at present!
The first point is knowledge. To that end I've found on this site and through google a couple of links that look quite helpful.

Tools and training videos on how to use them here:
http://tangentsoft.net/audio/new-diyer.html

amp electronics primer here
http://www.bcae1.com/repairbasicsfor...pairbasics.htm

I've also got lots of old computer pcbs to practice/develop soldering skills.

I've definitely got a lot to learn but really need to try and get one amp working so any advice would be greatly appreciated.

Thanks
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Old 5th September 2009, 03:53 PM   #5
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Join Date: Aug 2009
Location: West Midlands
hello again,
firstly then you will need to get some tools - dont have to be expensive but if you are thinking of doing a lot of this type of thing then it is worthwhile investing in some decent ones.
in terms of soldering i would recommend a temp controlled station of no less than 50watts. also make sure you buy some solder mop to remove the solder already in use on the PCB so that you can remove faulty components.

right lets concentrate on the Tempest first as I am 95% sure that the input selector is the source of your problems. I have included several photos of the input selector i removed from my Pioneer A400 (not because it was faulty but to improve sound).
The photos do show that the part was deteriorating though and that some of the parts are quite flimsy. The last of the photos shows an existing selector on the PCB next to the one i have replaced - i simply hardwired the desired input with solid silver wire.

Click the image to open in full size.

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so, once you have all the tools you need now you should have some idea what to look for. after that you can remove the part and disassemble it to check it is faulty. then contact MF to see if they stock or can locate a replacement. If not then you can do what I did and just hardwire one (yes only one)of the inputs.
let me know how you get on.
Chris
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Old 5th September 2009, 07:51 PM   #6
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Thats great, I really appreciate your help

I did some thorough testing last night and my tempest has deteriorated again in some respects. The results are strange and I was wondering if you think its still that problem?

Sources:
1 - PC
2 - Technics SLPG520A
3 - Marantz CD63 mk2

Test: Audiolab:-
Technics produces sound from both speakers when connected to Tape 1 or Tape 2
PC produces sound in only left speaker
Marantz produces sound in only left speaker

Test: Tempest:-
After much cable changing the condition of the tempest has worsened and now produces the same results as for the Audiolab, in that only the Technics can produce sound from both speakers on any input channel

Notes:-
I have swapped all interconnects to no effect.
I have also observed on the Audiolab that the left Tape 1 Line in connection has some give in it causing the left channel to cut out depending on which way it is leaning.

So I'm stuck. How can both amps be having the same problem (or showing the same symptoms) and that no other source works other than the Technics?

Thanks again
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Old 6th September 2009, 07:48 AM   #7
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Location: West Midlands
Hello again, i think you will have to open both amps up and start to have a close look at the solder joints on the underside of the PCBs. If you google "dry solder joints" for images you will see plenty of pics demonstrating what dry or damaged solder joints look like.
What you describe in regards to the Tape 1 Line in problem is a perfect example of a symptom a dry or damaged solder joint - solder joints are not able to withstand unlimited pressures.
in the mean time i would also take both the marantz and technics to a friends house and try them on their amp to make sure its not your sources playing up.
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Old 6th September 2009, 11:49 AM   #8
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Thanks.
Dry solder joints googled and understood.
Opened Tempest up.
Had a look at the top side first (after cleaning off the thick layer of dust and dead moth) and noticed this....
Click the image to open in full size.

I've always checked PC motherboards for swelling or leaking capacitors but this is the first time I've ever found anything - but I'm guessing this is the latter. It is a capacitor right?! Oh the shame of my ignorance.

So to resolve it, its find the exact same 'capacitor' either from the likes of maplin or Musical Fidelity and solder it in right?

Not yet had a look underneath the board - will need a few hours to try and dismantle it to get there - time I dont have just now.

But I will keep looking as although it is a problem it may not be the only one...
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Old 6th September 2009, 08:21 PM   #9
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OMG - yeah a leaking capacitor that is and it certainly wont have been helping things! however, i would keep looking as i would be very surprised if that was the only thing that has gone wrong.
the capacitor will have its value written on it as well as its voltage. make sure to match these when replacing - though normally a slightly higher voltage will be no problem. only thing is that the circuit board may be too damaged for you simply to drop it back in. i would remove the old cap using a soldering iron and solder mop then clean up the area to assess that you can make a successful joint again.
to be honest though there would be no shame in you taking it to a pro to be looked at as you might be wading in too deep for a first timer...
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Old 7th September 2009, 06:35 AM   #10
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To be honest mate, I'm really enjoying this, and so far... so easy. Although without your guidance I'd be nowhere - so my thanks.

First a question, how can a circuit board be too damaged to just drop a new capacitor back in?

Ok a further observation on the top side of the amp is that 3 parts of the board have turned brown. On closer inspection there is a resistor at the centre of each patch that have all cracked. Is this bad?
The resistors are all marked the same which if I recall correctly designates the resistance. The fourth resistor of that type - of which there are only 4 on the board - is also cracked, although there are no signs the board has turned brown around it.
No other resistors have cracked up.

Heres a pic of one of them...
Click the image to open in full size.

So I'm guessing these resistors would need to be replaced, along with a 5th which is a different resistor but has cracked a little from being adjacent to one of these. Heres a pic of it, its the one at the top - worth replacing?
Click the image to open in full size.

So how do I identify what they are and what they should be replaced with?
Now if the dry solder joints are literally dry then I'm guessing I'll find a lot of them in the 'burned' areas of the board - when I finally manage to get it out the box.

Another question, the amp is about 18 years old now, is it advisable to replace any other capacitors or anything else that may also deteriorate with age?


UPDATE

I've had a look under the board and got a bit of a surprise. It seemed to be covered in gunk as if someone had poured a glass of coke over the amp at some point. What is this?
Click the image to open in full size.

close up of gunk...
Click the image to open in full size.

I looked for dried solders and I think I may have found a couple at the point where the resistors burned the board. Would you agree that thats what they are?
Click the image to open in full size.

Also there is no sign of any damage on the underside of the board where the capacitor leaked.


So what now?
1 - Find out what the gunk is and if its meant to be there. If not then how to clean it off?
2 - find replacement resistors/capacitors and anything else I may need
3 - get a soldering iron + desolder braid thing. What actual solder would I need to get for hi-fi?
4 - Enjoy my music once more!


Thanks again
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