I have a SX-727 that I've owned for around ten years, for the last 6 or so it has been in storage but I've recently set it up again. I've been having some problems with the left channel, sometimes it will work for a short time when I turn on the unit, other times it will be extremely quiet (only audible when the balance dial is turned all the way to the left. Once while listening, the left channel slowly faded out, over about 3 or four seconds. Aside from this issue, there are no crackles, pops or hiss.
I've checked all the front panel switches (mono, loudness etc) and they function as expected but do not "wake" the left channel. If I connect directly to the power amp by removing the rear jumpers, both left and right channels function just fine, which leads me to think there is a problem in the preamp section.
I plan to open up and clean the unit but while I am at it I might as well replace the caps, indeed reading similar threads about this unit suggests that this would be a good idea. moped's thread from 2011 (appearing to have an identical problem) has been really useful, as is the cap BOM provided by MTF in the same thread.
I've been creating an order through mouser wth MTF's BOM as a guide. I've pasted MTF's list below, with my ammendments based on 2020 availability. The bottom two entries are transistors which MTF recommends replacing, unfortunately the KSC1845EBU is not available on mouser, and I see no obvious substitute on the site. It is however readily available on ebay and other sites so not a big problem.
Some of the caps I have subbed with other parts with seemingly identitcal specifications, but with the 1TD designator at the end. I've not been able to find exactly what this means, I did read somewhere that the legs might be very short, but I don't think that is the case. If anyone knows, I'd be interested to find out.
The 598-DSF050J474 4 // substituted to B32529C474J was recommended as a substitute from another AK thread.
the one substitution I am not sure about is the 647-UPW1H010MDD 3 // substituted to 647-ULD1H010MDD1TD - the sub version appears to be identical except that it has a ripple current rating of 25ma as opposed to the 40ma in the original. These three caps are intended for the tuner.
My questions:
1. Does my below list look ok, and are the substitutions ok?
2. MTF mentions "skip the tuner - you don't need that grief" -I don't really use the tuner. Can I assume this means it's not worth replacing parts on the tuner board (overly fiddly perhaps?) Presumably it has a separate signal path which does not affect the other sections?
3. Based on my description of the problem are there any other parts that might be worth ordering?
for anyone who is interested, I have the below list in google sheets, also detailing which caps go on which board
647-UPW2A102MHD 1
647-UPW1E470MDD 3 // substituted to UPW1E470MDD1TD (reason, availability)
647-UVZ1J682MRD 2
647-UPW1C471MPD 2
647-UPW1H100MDD 4
647-UPW1J221MPD6 1
647-UPW1H101MPD 4
647-UKL1H2R2MDDANA 8
647-UKL1H3R3KDDANA 2
647-UPW1V101MPD 3
598-DSF050J474 4 // substituted to 871-B32529C474J (reason, obsolete)
647-UPW1V220MDD 4
647-UPW1A101MDD 2
647-UPW1V221MPD 4
647-UPW1H4R7MDD 6 // substituted to UPW1H4R7MDD1TD (reason, availability)
647-UPW1H470MED 4
647-UPW1A221MED 3
647-UPW1H010MDD 3 // substituted to 647-ULD1H010MDD1TD (reason, availability)
647-UPW1E331MPD6 1
KSA992FBU 2
KSC1845EBU 8 // no availability on mouser - ebay?
thanks in advance for any help.
I've checked all the front panel switches (mono, loudness etc) and they function as expected but do not "wake" the left channel. If I connect directly to the power amp by removing the rear jumpers, both left and right channels function just fine, which leads me to think there is a problem in the preamp section.
I plan to open up and clean the unit but while I am at it I might as well replace the caps, indeed reading similar threads about this unit suggests that this would be a good idea. moped's thread from 2011 (appearing to have an identical problem) has been really useful, as is the cap BOM provided by MTF in the same thread.
I've been creating an order through mouser wth MTF's BOM as a guide. I've pasted MTF's list below, with my ammendments based on 2020 availability. The bottom two entries are transistors which MTF recommends replacing, unfortunately the KSC1845EBU is not available on mouser, and I see no obvious substitute on the site. It is however readily available on ebay and other sites so not a big problem.
Some of the caps I have subbed with other parts with seemingly identitcal specifications, but with the 1TD designator at the end. I've not been able to find exactly what this means, I did read somewhere that the legs might be very short, but I don't think that is the case. If anyone knows, I'd be interested to find out.
The 598-DSF050J474 4 // substituted to B32529C474J was recommended as a substitute from another AK thread.
the one substitution I am not sure about is the 647-UPW1H010MDD 3 // substituted to 647-ULD1H010MDD1TD - the sub version appears to be identical except that it has a ripple current rating of 25ma as opposed to the 40ma in the original. These three caps are intended for the tuner.
My questions:
1. Does my below list look ok, and are the substitutions ok?
2. MTF mentions "skip the tuner - you don't need that grief" -I don't really use the tuner. Can I assume this means it's not worth replacing parts on the tuner board (overly fiddly perhaps?) Presumably it has a separate signal path which does not affect the other sections?
3. Based on my description of the problem are there any other parts that might be worth ordering?
for anyone who is interested, I have the below list in google sheets, also detailing which caps go on which board
647-UPW2A102MHD 1
647-UPW1E470MDD 3 // substituted to UPW1E470MDD1TD (reason, availability)
647-UVZ1J682MRD 2
647-UPW1C471MPD 2
647-UPW1H100MDD 4
647-UPW1J221MPD6 1
647-UPW1H101MPD 4
647-UKL1H2R2MDDANA 8
647-UKL1H3R3KDDANA 2
647-UPW1V101MPD 3
598-DSF050J474 4 // substituted to 871-B32529C474J (reason, obsolete)
647-UPW1V220MDD 4
647-UPW1A101MDD 2
647-UPW1V221MPD 4
647-UPW1H4R7MDD 6 // substituted to UPW1H4R7MDD1TD (reason, availability)
647-UPW1H470MED 4
647-UPW1A221MED 3
647-UPW1H010MDD 3 // substituted to 647-ULD1H010MDD1TD (reason, availability)
647-UPW1E331MPD6 1
KSA992FBU 2
KSC1845EBU 8 // no availability on mouser - ebay?
thanks in advance for any help.
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