david ellwood
Kirabosi Kognoscente
Next step is to check voltages across the board
Meridian 206 CDP ...partial success
- Thread starter Chris Tarling
- Start date
john.luckins
pfm Member
This may be normal but the pcb to the rear of the DAC chip is darkened. A hot IC can dry out the joints around it so they are worth checking and re-soldering if they don't look clear and shiny. I would suggest checking that each Integrated Circuit is getting power. That'll mean googling for each of the data sheets and then very carefully measuring the voltage on the power pin(s) with respect to earth while the unit is powered up. Also see if anything is getting particularly hot when powered up. Further checks beyond that are going to need a scope. BTW there's a lot of solder flux on the clock board that needs to be removed with a good scrub with some alcohol.
John
John
david ellwood
Kirabosi Kognoscente
Where in the country are you? There may be a capable fishie local to you!
Chris Tarling
Yellow Hound
Cheltenham, Glos
david ellwood
Kirabosi Kognoscente
I’m up int north, anyone?
john.luckins
pfm Member
I'm a little closer in East Northants but snowed under with similar jobs for friends at the moment.
martin clark
pinko bodger
Bath, c. an hour away; happy to help if I can.
a.palfreyman
pfm Member
E Mids I'm afraid.
Chris Tarling
Yellow Hound
Thanks all - I am touched by your kindness.
@martin clark I'm going to see how I can get on but might need to call on your help!
@martin clark I'm going to see how I can get on but might need to call on your help!
Chris Tarling
Yellow Hound
I have had a further good look at the TDA chip soldered connections and they all look nice and shiny.
david ellwood
Kirabosi Kognoscente
This is where you need an oscilloscope to trace signals across the board.
a.palfreyman
pfm Member
As has been said above a DVM to check the supply voltages to the chips would be a good place to start. I'm not familiar with the unit, but the fact that the optical out is working suggests the SAA7220 (adjacent to the TDA 1541A) is working which points to the TDA or the output stage which appears to be the cluster of transistor adjacent to the TDA.
Chris Tarling
Yellow Hound
Thank you.
I shall start my investigation there.
As a matter of more general interest, are TDA1541A chips available from any reliable source?
I think this is the right forum to find someone able to supply such a chip. They've not been made for years, and in reality the most likely place to get one from would be salvaged from another player. The crown version you currently have is a premium version, although later non-crown chips can perform very well (they were graded from the production line as crown chips, nothing special about how they were manufactured, more that the best of the batch were labelled as crown). It's possible that they didn't have so much demand for crown versions so plenty of normal ones actually perform very well
a.palfreyman
pfm Member
Dowser
Learning to bodge again..
Have you got the +/-5v and -15v rails into the 1541? And make sure power rails of opamps have their +/- feeds.
given digital out works, it can only be DAC chip, output stage or cpu intentionally muting for some reason (unlikely). I have had a faulty 1541 do this before…shame if so, it’s a nice S1
Start by checking voltages.
Good luck, Richard
given digital out works, it can only be DAC chip, output stage or cpu intentionally muting for some reason (unlikely). I have had a faulty 1541 do this before…shame if so, it’s a nice S1
Start by checking voltages.
Good luck, Richard
Chris Tarling
Yellow Hound
Looking at the TDA1541A I have:
+5V at pin 28
-5V at pin 26
-15V at pin 15
These are all to spec.
There are two opamps in the analogue circuit. I have replaced both, now mounted on sockets soldered to the board. Both are now LME49720. One was previously an LF353N, the other an NE5532N.
Both have +/-V input and are giving output voltages.
+5V at pin 28
-5V at pin 26
-15V at pin 15
These are all to spec.
There are two opamps in the analogue circuit. I have replaced both, now mounted on sockets soldered to the board. Both are now LME49720. One was previously an LF353N, the other an NE5532N.
Both have +/-V input and are giving output voltages.
Mike P
Trade: Pickwell Audio
Have you got dead silence on the analogue output or do you have some noise?
The typical failure mode of the TDA1541 is that you get some noise/hiss that slowly gets worse over time and tends to get worse as the player warms up. Eventually you'll only have noise and no music.
As others have already said, an oscilloscope for tracing the signals is what you really want.
Provided you're very confident in your ability remove the DAC chip, without causing any damage there's no harm in doing so. Fit a socket and you can then try a replacement chip that's known to be good, to see if that fixes it. If it doesn't work you've only spent a few quid on an IC socket.
It'd be well worth making the effort to get to Martin.
The typical failure mode of the TDA1541 is that you get some noise/hiss that slowly gets worse over time and tends to get worse as the player warms up. Eventually you'll only have noise and no music.
As others have already said, an oscilloscope for tracing the signals is what you really want.
Provided you're very confident in your ability remove the DAC chip, without causing any damage there's no harm in doing so. Fit a socket and you can then try a replacement chip that's known to be good, to see if that fixes it. If it doesn't work you've only spent a few quid on an IC socket.
It'd be well worth making the effort to get to Martin.
Is there a relay on the output of this player? Might be that there's a proper signal making it to within an inch of the connectors then stopping. As has been mentioned, an oscilloscope is probably the next tool you need to either borrow or get the player to someone so equipped.
martin clark
pinko bodger
Are those output voltages stable,as far as you can tell, on ac mv scale..? What DC V readings do you 'see' on the output pins,and are they very very stable?
While the opamps are all pin-compatible, there is a heckuva difference between the bandwidth (and decoupling) sensitivities of the old LF353 and the LME49720. The 206 board layout is old-school, and the supply rail bypass caps ... possibly too physically remote to serve the bandwidth demands of modern/faster opamps.
So - I'm wondering if the latter are simply oscillating at HF and that's blocking/saturating their output. Easiest check, after reporting DC v on the output pins and whether it is wobbling about while you watch the meter..: are the installed new opamps all running at low temps ?
Put a finger on each after a couple of minutes of power-up: they should really only be body temp or about that, max,; nothing hot - which is a classic sign of HF oscillation.