Leak stereo 70 fault

harrygrey382 · 24th February 2007, 03:44 PM

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

poynton · 24th February 2007, 04:06 PM

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

harrygrey382 · 24th February 2007, 04:22 PM

yes it does, that's how i traced it to the preamp board

so where to now if you don't mind me asking?

coolmaster · 24th February 2007, 05:00 PM

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.

teemuk · 24th February 2007, 05:13 PM

Save yourself from the trouble. Here's a link to it:
http://home.vicnet.net.au/~vic3d/aud...ctStereo70.gif

poynton · 24th February 2007, 06:24 PM

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

latala · 24th February 2007, 06:26 PM

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

consort_ee_um · 24th February 2007, 06:46 PM

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

big jim · 25th February 2007, 08:48 AM

Hi harry
i have a pre amp pcb i think its ok
and its yours for free if you want it

good luck jim

harrygrey382 · 25th February 2007, 09:19 AM

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!

24th February 2007, 03:44 PM	#1
harrygrey382 diyAudio Member Join Date: Jun 2006	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

24th February 2007, 06:24 PM	#6
poynton Magneto the Gravity Man diyAudio Member Join Date: Mar 2005 Location: A life on the ocean waves when I'm not at home in N. Wales (but I'm not Welsh so no sheep jokes!)	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 __________________ If it ain't broke, break it !! Then fix it again. It's called DIY !

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24th February 2007, 04:22 PM	#3
harrygrey382 diyAudio Member Join Date: Jun 2006	yes it does, that's how i traced it to the preamp board so where to now if you don't mind me asking?

24th February 2007, 05:00 PM	#4
coolmaster diyAudio Member Join Date: Jul 2005 Location: MY	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.

24th February 2007, 05:13 PM	#5
teemuk diyAudio Member Join Date: Nov 2004 Location: Suomi, Finland	Save yourself from the trouble. Here's a link to it: http://home.vicnet.net.au/~vic3d/aud...ctStereo70.gif

24th February 2007, 06:26 PM	#7
latala diyAudio Member Join Date: Feb 2006 Location: staffordshire	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

24th February 2007, 06:46 PM	#8
consort_ee_um diyAudio Member Join Date: May 2004 Location: Hertfordshire	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

25th February 2007, 08:48 AM	#9
big jim diyAudio Member Join Date: Feb 2006 Location: london	Hi harry i have a pre amp pcb i think its ok and its yours for free if you want it good luck jim

25th February 2007, 09:19 AM	#10
harrygrey382 diyAudio Member Join Date: Jun 2006	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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