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Old 24th February 2007, 03:44 PM   #1
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Default Leak stereo 70 fault

Hi,
I have the classic scenario: Old SS amp with a faulty channel (v quite, but sitll sound coming from it). It's a Leak Stereo 70 integrated amp. I've traced the fault to one of the preamp circuit boards.
Now how do I begin tracing the faulty componet? It's resistors, capacitors and a couple of little other components, not sure what they are. Anyone got some thoughts?
Also, there's a higgh pitched whine that increased with volume. It's inaudible under music though. Would anyone be able to hazard a guess over what could be causing this?
Thanks
Harry
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Old 24th February 2007, 04:06 PM   #2
poynton is offline poynton  United Kingdom
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Default Re: Leak stereo 70 fault

Quote:
Originally posted by harrygrey382
I've traced the fault to one of the preamp circuit boards.
I assume that you have swapped boards.

Does the fault ''change channels'' when you swap ??

Andy
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Old 24th February 2007, 04:22 PM   #3
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yes it does, that's how i traced it to the preamp board
so where to now if you don't mind me asking?
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Old 24th February 2007, 05:00 PM   #4
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Considering the age of it, and if parts were never replaced before, if I were you, replace ALL the electrolytic capacitors with modern compatible parts for a start. At least that'll give it a new lease of life, lessen trouble in future, mandatory if its more than 20 years old or with a doubtful service history.
If you need a copy of the manual/schematic/layout, message me. I'll gladly let you have it.
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Old 24th February 2007, 05:13 PM   #5
teemuk is offline teemuk  Finland
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Save yourself from the trouble. Here's a link to it:
http://home.vicnet.net.au/~vic3d/aud...ctStereo70.gif
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Old 24th February 2007, 06:24 PM   #6
poynton is offline poynton  United Kingdom
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HI.

for a start, I would use a 'calibrated finger' on the bass/treble control contacts and compare the volume of the resulting hum between good and bad channels.

A better method would be to play a cd, and use a probe - wire plus cap- between the hot end of the vol and the input progressively working back until the sound fades or disappears.

Andy
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Old 24th February 2007, 06:26 PM   #7
latala is offline latala  United Kingdom
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Yes I generally agree with the capacitors being at fault I have had to replace quite a few of these during my previous life as an audio engineer !
To second it I would also measure the collector voltages on all the transistors as I have had a few of these go open circuit re the base emitter junction.
Never my favourite amplifier but none the less worth restoring
regards Trev
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Old 24th February 2007, 06:46 PM   #8
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As Trev says about the transistors. In particular T7 is stressed since it is rated at 65V and the supply is 75V! Mind you T7 is not on the pre-amp board so it cannot be that. Love those old transistor symbols in the circuit diagram
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Old 25th February 2007, 08:48 AM   #9
big jim is offline big jim  England
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Hi harry
i have a pre amp pcb i think its ok
and its yours for free if you want it


good luck jim
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Old 25th February 2007, 09:19 AM   #10
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Brilliant Jim, I'd love it!
I don't really have time to get to London at the moment though. Is there any chance you could drop it in the post? I could send you a paypal/cheque/give some money to charity...
Thanks a lot, these forums can be so fantastic at connecting people!
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