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
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
harrygrey382 said:
I assume that you have swapped boards.
Does the fault ''change channels'' when you swap ??
Andy
yes it does, that's how i traced it to the preamp board 😉
so where to now if you don't mind me asking?
so where to now if you don't mind me asking?
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.
If you need a copy of the manual/schematic/layout, message me. I'll gladly let you have it.
Save yourself from the trouble. Here's a link to it:
http://home.vicnet.net.au/~vic3d/audio/leak/cctStereo70.gif
http://home.vicnet.net.au/~vic3d/audio/leak/cctStereo70.gif
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
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
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
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
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
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!
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!
meanwhile I spose I will start looking at replacing caps. Away from the unit for the weekend so not sure which ones you're meaning. And I do have the original manual inc. circuit diagram 🙂
I'm also thinking replacing all the caps (including the dimensionally MASSIVE ones) with new audio grade ones is going to come up about the price of a decent second amp...
Andy, what is a 'caliberated finger'.
Trevor, forgive my ignorance (still sometimes finding my way in DIY) but what's the method for finding the collector voltage on the transistors? ALso do I measure all of them and what do they look like?
Thanks guys
I'm also thinking replacing all the caps (including the dimensionally MASSIVE ones) with new audio grade ones is going to come up about the price of a decent second amp...
Andy, what is a 'caliberated finger'.
Trevor, forgive my ignorance (still sometimes finding my way in DIY) but what's the method for finding the collector voltage on the transistors? ALso do I measure all of them and what do they look like?
Thanks guys
To be honest if you are not as yet compitent I would not start to measure voltages etc! As you can end up causing far more damage If you slip or miss-connect Its not uncommon to find that with respect "amatuers" can create far more damage!!!
While I am discussing this also always resist the temptation to swap boards on the power amp section I have had many a seventy/thirty come in where customers have done this and then blown the drivers on both cards this is because the outputs are at fault and they dont swap with the boards
By all means take up the offer on the preamp board this is a generous solution you could then change the caps etc
To be honest I think I have maybe 20 or so LEAK amps in my collection and I have had no problems with the large caps as yet so I would not bother to change them if the amp is ok
Regards Trev
While I am discussing this also always resist the temptation to swap boards on the power amp section I have had many a seventy/thirty come in where customers have done this and then blown the drivers on both cards this is because the outputs are at fault and they dont swap with the boards
By all means take up the offer on the preamp board this is a generous solution you could then change the caps etc
To be honest I think I have maybe 20 or so LEAK amps in my collection and I have had no problems with the large caps as yet so I would not bother to change them if the amp is ok
Regards Trev
Hi harry
please email me your address and i will post it to you
for free if you wish to cover the postage please donate to any cancer charity of your choice
all the best jim
please email me your address and i will post it to you
for free if you wish to cover the postage please donate to any cancer charity of your choice
all the best jim
well luckily the ouputs must be ok because I swapped the power amp boards and it's all still fine! I'll remeber that though. Agreed about the measuring voltage, I do have a steady hand but wouldn't want to short something by accident due to ignorance.latala said:
Thanks
harrygrey382 said:
Fitting general purpose grade capacitors (as long as its from reputable manufacturers like Elna, Rubycon, Nichicon, axial lead BHC, Philips or Evox Rifa) will work just fine. The original ones were not audio grade anyway, but there's no stopping you if you'd prefer to splash out for boutique ones.
On the contrary to what latala says, I wouldn't blink an eye to replace the big ones (mains filter caps) if they're more than 15 years old...especially if it were a Leak tube amp. I ain't risking the amp cooking something and get sleepless nights thereon.
Only recently, I just replaced the 2 big caps for a Quad 405 which was already bulging and signs of fluid leakage. The owner was completely ignorant and lucky for him, I spotted it soon enough. Those caps were big fat blue ones made by ITT and supposed to be of impeccable quality but yet..to me its fit for the garbage bin.
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I agree re comments changing capsfor leak tube amps but I have not had any problems re large caps on transistor LEAK,s
However when you talk Quad ,Armstrong we are on to another thing entirely,I have never had a big cap problem with a tranny Leak!
However if you see any sign of leakage or bulging change them
regards Trev
However when you talk Quad ,Armstrong we are on to another thing entirely,I have never had a big cap problem with a tranny Leak!
However if you see any sign of leakage or bulging change them
regards Trev
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