Hi all,
I recently bought a really rare Sony 702ES DAC (from 1983 - one of the world's first outboard DACs!) which has a problem - the right channel has no audio at all. The left channel works but you get a bit of static in the sound when it's cold.
I'm no electronics expert but I've had the lid off and done a visual check and everything looks okay. I notice that one of the two DAC chips gets really hot but the other one doesn't.
Apparently this is very similar to the 703ES DAC.
Anyone got any ideas of where I could start?
Thank you.
I recently bought a really rare Sony 702ES DAC (from 1983 - one of the world's first outboard DACs!) which has a problem - the right channel has no audio at all. The left channel works but you get a bit of static in the sound when it's cold.
I'm no electronics expert but I've had the lid off and done a visual check and everything looks okay. I notice that one of the two DAC chips gets really hot but the other one doesn't.
Apparently this is very similar to the 703ES DAC.
Anyone got any ideas of where I could start?
Thank you.
You are posting in too many threads asking for the same info. Did you get a copy of the service manual yet?
I have a copy of the service manual but I’m not experienced with electronics so much of it is somewhat over my head!
Well, you say one dac chip is hot and the other is not, so you know which chips are the dac chips? Did you get a copy of the dac chip data sheet?
so .... what kind of experience do you have? it will be a problem if you can't read through the service manual and at least be able to take some voltage measurements and report what you find.
Ok so I’m aware of the basics but working with digital-based devices like this is new to me. As far as I can tell the voltages appear to be right for the most part. They seem different for the two DAC chips (PCM53) though - for example pin 18 has 14.4v on one chip and around 5v on the other.
I was thinking of swapping the two DACs around and seeing if the fault followed as a starting point. Would this make sense?
I was thinking of swapping the two DACs around and seeing if the fault followed as a starting point. Would this make sense?
Before swapping any chips, the crackling and warming up behavior you described for the working channel makes me suspicions of power supplies first. I would suggest checking them, especially old electrolytic capacitors and possibly bad connections if power supply rails pass through any connectors.
So I've been doing a bit more investigation. There appears to be continuity between pins 18 and 19 on the offending DAC chip - details on page 3 here:
http://vasiltech.narod.ru/files/PCM53.pdf
And this isn't the case on the "working" side. The offending side is also the one that gets particularly hot.
Here is a screenshot from the relevant part of the circuit diagram for the DAC:
I've checked the voltage regulator and there is no continuity between any of its pins. I haven't yet removed the capacitor to check that.
Bearing the above in mind, does it sound like the DAC chip is somehow internally damaged causing the short between its pins?
http://vasiltech.narod.ru/files/PCM53.pdf
And this isn't the case on the "working" side. The offending side is also the one that gets particularly hot.
Here is a screenshot from the relevant part of the circuit diagram for the DAC:
I've checked the voltage regulator and there is no continuity between any of its pins. I haven't yet removed the capacitor to check that.
Bearing the above in mind, does it sound like the DAC chip is somehow internally damaged causing the short between its pins?
Not according to the datasheet and the schematic above. Unless I'm missing something.
The single power supply seems to feed both DACs.
My eyesight problem along with a fuzzy DS copy, hence I deleted the post.
If there's true continuity (i.e. a short) between pins 18 & 19 then they'll be approximately the same voltage. But you report +5V on one, +14.4V on another pin 18. Whereas pin19 should be -14.4V.
You haven't yet said which of the two DAC chips is the one getting hot IC102 or IC202? If you were to show the schematic around IC102 we could then determine if pin18 is designed to be at a different voltage on the two chips.
If there's true continuity (i.e. a short) between pins 18 & 19 then they'll be approximately the same voltage. But you report +5V on one, +14.4V on another pin 18. Whereas pin19 should be -14.4V.
You haven't yet said which of the two DAC chips is the one getting hot IC102 or IC202? If you were to show the schematic around IC102 we could then determine if pin18 is designed to be at a different voltage on the two chips.
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No worries 🙂
Grateful for any other pointers of what to look at. This is my first time attempting to repair something so you'll have to forgive the newbie questions/comments.
Grateful for any other pointers of what to look at. This is my first time attempting to repair something so you'll have to forgive the newbie questions/comments.
Is C206 shorted, or did you measure with the dac chip removed from the circuit? How are you measuring?
Right I've removed the capacitor C206 and it is indeed shorting. Now that it's removed, the pins on the DAC no longer short.
So I need to replace this capacitor and hope that it sorts it, and hope that the DAC chip isn't fried.
It looks like below. Any idea how I go about finding a replacement? My Google-Fu is failing. According to the service manual it's "Tantalum 10mF 25% 20V"
So I need to replace this capacitor and hope that it sorts it, and hope that the DAC chip isn't fried.
It looks like below. Any idea how I go about finding a replacement? My Google-Fu is failing. According to the service manual it's "Tantalum 10mF 25% 20V"
From looking at the service manual parts list, it appears that MF is being used to mean uf. If so, there are lots of 10uf tantalums to pick from at Mouser and Digikey. Possibly a good idea to change the one for other channel too since that one failed?
Thank you! I can't find any 10uF tantalums that look like the ones above, they're either surface mount or they look like this:
Will these be a suitable substitute? I believe this one is polarised unless I'm reading it wrong so I guess I need the same?
Also.. OH MY GOD I powered it up without the cap in place briefly, and IT WORKS! Both channels sing beautifully! It's now powered off until I can replace the cap.
Will these be a suitable substitute? I believe this one is polarised unless I'm reading it wrong so I guess I need the same?
Also.. OH MY GOD I powered it up without the cap in place briefly, and IT WORKS! Both channels sing beautifully! It's now powered off until I can replace the cap.
and possibly damage what might be a good device?
making your troubleshooting even harder?
Edit:
Never mind; I see you didn't and made some progress.
Bet you're glad you didn't change DACs!
making your troubleshooting even harder?
Edit:
Never mind; I see you didn't and made some progress.
Bet you're glad you didn't change DACs!
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Tantalums are polarized. The beveled corner on the old one is probably to help orient the part correctly on the PCB.
Regarding a new cap, so long as it fits in the space it should work pretty much the same as the old one. However, if you have a part number for the voltage regulator then you might look up its data sheet and see if it says anything about output caps. Some regulators care what capacitor ESR is, for example. Otherwise you might check the output node with a scope after replacing the cap to make sure no oscillation, etc.
Regarding a new cap, so long as it fits in the space it should work pretty much the same as the old one. However, if you have a part number for the voltage regulator then you might look up its data sheet and see if it says anything about output caps. Some regulators care what capacitor ESR is, for example. Otherwise you might check the output node with a scope after replacing the cap to make sure no oscillation, etc.
I looked at the NJM78M20 reg's DS - it only mentions a 0.1uF output cap. Nothing about ESR so presumably not that critical.
The tantalum you show would be an acceptable substitute - but the shorted one in your picture is 25V (not 20V). I'd suggest a minimum 25V replacement.
The tantalum you show would be an acceptable substitute - but the shorted one in your picture is 25V (not 20V). I'd suggest a minimum 25V replacement.