Hi Guys, seeking some expertise if I may please.
I inherited this DAC about 2 years back.. Issues were:
very old caps and burnt transformers
A regulator seemed the input and output was shorted
High DC on LEFT (I think) Channel
I noticed one diode right at the bottom of the board was in the wrong way round from factory!
I took out all transformers ( I have no idea why I did that) I recapped it and tested it without doing anything else. It was exactly the same as before but still one channel had very high DC. I cant remember the exact figure it may have been 2-400mv. Other channle was 1mv or less.
I removed the short and fixed the diode orientation and it worked for a minute then hasn't worked since. I have attached an internet picture of the board with caps removed. The regulator furthest left was shorted input and output. I have actually put that back the way it was and still nothing.
It seems I'm not getting a 5v supply. the SMD LM317 I removed and replaced already supplys the 5v+ rail. Looking atdatasheet the first pin is getting 6-7v but 0.1v output. It seems output is shorted to ground. I replaced the chip and pretty much everything around it and they all measure fine.
It has taken me over a year to do all this and I have no idea why the diode was inserted the wrong way or what kind of damage that has caused.
I just know pin 2 of TDA1547 should be 5v+ and its not. This may be blindly obvious to someone so any help would be greatly appreciated. Currently I'm just testing the DAC with a few test transformers and one channel works very well and actually sounds excellent but the lower channel nothing.
I inherited this DAC about 2 years back.. Issues were:
very old caps and burnt transformers
A regulator seemed the input and output was shorted
High DC on LEFT (I think) Channel
I noticed one diode right at the bottom of the board was in the wrong way round from factory!
I took out all transformers ( I have no idea why I did that) I recapped it and tested it without doing anything else. It was exactly the same as before but still one channel had very high DC. I cant remember the exact figure it may have been 2-400mv. Other channle was 1mv or less.
I removed the short and fixed the diode orientation and it worked for a minute then hasn't worked since. I have attached an internet picture of the board with caps removed. The regulator furthest left was shorted input and output. I have actually put that back the way it was and still nothing.
It seems I'm not getting a 5v supply. the SMD LM317 I removed and replaced already supplys the 5v+ rail. Looking atdatasheet the first pin is getting 6-7v but 0.1v output. It seems output is shorted to ground. I replaced the chip and pretty much everything around it and they all measure fine.
It has taken me over a year to do all this and I have no idea why the diode was inserted the wrong way or what kind of damage that has caused.
I just know pin 2 of TDA1547 should be 5v+ and its not. This may be blindly obvious to someone so any help would be greatly appreciated. Currently I'm just testing the DAC with a few test transformers and one channel works very well and actually sounds excellent but the lower channel nothing.
Attachments
Hi, if you look at the internet photo without the caps you can clearly see the alignment of all the diodes. On the farthest right that was in the wrong way round on mine and I believe that was the cause of the high DC
Have to ask what you are using to solder, what kind of solder and tools, and do you have isopropyl alcohol to clean up some of the flux? Reason I ask is the pics look rather worrisome in terms reliability and functionality. Maybe we can help you get that looking a little better. Also if it were cleaner it might help with troubleshooting.
Also, if you could circle the diode that was reversed, might help to confirm the one you mean.
Also, if you could circle the diode that was reversed, might help to confirm the one you mean.
yes I have those. The board was in a cupboard for 2 years, explains the dust but not the flux I guess. Its a lovevly looking DAC, wooden case.
See attached with the diode. The solder that is shorting the input and output of the LM317 is actually normal as I have seen in another forum (maybe where I got the pic) someone mentioned it. I think it was this forum actually as I messaged the guy but he can't remember about it.
See attached with the diode. The solder that is shorting the input and output of the LM317 is actually normal as I have seen in another forum (maybe where I got the pic) someone mentioned it. I think it was this forum actually as I messaged the guy but he can't remember about it.
Attachments
I will dig it out tomorrow and clean it up as much as I can in that area. I made an error I just removed the parts and tested it and not replaced it as stated above, I only replaced the LM317LM SMD LM317 with new.