Hi, I ordered 2 MC74HC595 today, to see if its replacement can help. My thought is that the values measured - with the scope - on 3 outputs of this shift register do not look like they should, see schematics. The optocouplers seem to be working correctly, both inputs and outputs, as far as I can judge after trials.
Here is the latest version of it.
Here is the latest version of it.
Attachments
Hello everyone, I just replaced the shift register 74HC595 with no better result...
A few things remain unclear to me:
Good day!
A few things remain unclear to me:
- when I measure voltage on pin 1 and 2 (shift register), either I've got 0V or 5V depending on what I'm doing with the remote, BUT the voltage remains the same as long as I don't press again a button on the remote. As if it keeps memory of it as long I didn't press the button another time. I don't see clearly why. Something related with the latch clock behavior? I didn't test all outputs, I'll do it more seriously this afternoon.
- I don't see any decoupling capacitor on that IC, against usual practice. Then I tried to put temporarily a 10nF ceramic on ground and Vcc to see if something would change, but no. Maybe I should try a 0.1µF. Or is it not recommended? I can't think that Wadia has forgotten to put one here's there are decoupling SMD caps everywhere...
- I'm waiting for 3 optocouplers (and a real Texas Instruments 74HC595 too) from Mouser next Monday. Maybe I should prepare DIP-8 supports in advance.
Good day!
Attachments
IT WORKS!!!!!
IT WORKS. IT WORKS.
I've replaced the 3 optocouplers (U42, U43, U44 on the schematics) and it works. I didn't soldered them, I chose to plug them on DIP-8 good quality sockets. As I did for the shift register.
I had some difficulties to unsolder the old ones, but I could finally make it and keep the PCB in good (enough) shape. Vias are really small so it's not super easy. That's the kind of moment when I don't regret having a Metcal desoldering station!
I'll post more pictures later after reassembling the rest of the feet and screws etc.
Once again, thanks @purer for your suggestions! You were absolutely right.
Good evening everyone.
IT WORKS. IT WORKS.
I've replaced the 3 optocouplers (U42, U43, U44 on the schematics) and it works. I didn't soldered them, I chose to plug them on DIP-8 good quality sockets. As I did for the shift register.
I had some difficulties to unsolder the old ones, but I could finally make it and keep the PCB in good (enough) shape. Vias are really small so it's not super easy. That's the kind of moment when I don't regret having a Metcal desoldering station!
I'll post more pictures later after reassembling the rest of the feet and screws etc.
Once again, thanks @purer for your suggestions! You were absolutely right.
Good evening everyone.
Thanks @purer, I'm (very) glad too!
I replaced the 1Ω 2W resistor near the 5V supply first, not that it was bad, but to put it away from the board as it runs quite hot.
I bought the caps to replace them but didn't do it yet. I measured ESR of the three "big ones" and it was good so it's not an emergency I think. I wanted to replace all the small caps (47, 100µF) near to the 4 PCM1702. I've seen on pictures of the 861 that these caps were organic polymer caps (vs EL aluminium standard caps on the W16) and I think it's a better choice. I'll probably buy a bunch of them and do that work later.
Have a good day!
I replaced the 1Ω 2W resistor near the 5V supply first, not that it was bad, but to put it away from the board as it runs quite hot.
I bought the caps to replace them but didn't do it yet. I measured ESR of the three "big ones" and it was good so it's not an emergency I think. I wanted to replace all the small caps (47, 100µF) near to the 4 PCM1702. I've seen on pictures of the 861 that these caps were organic polymer caps (vs EL aluminium standard caps on the W16) and I think it's a better choice. I'll probably buy a bunch of them and do that work later.
Have a good day!
I'm rather sure that mine is just like yours @rockeater, even if I've got no precise picture of that specific area. What I'd recommend to @tolas123 is to have a look at the schematics (I must have put all documents I have online, just a small search would lead you to it) and have a look at this part of the schema. I'll have a look myself later when I got a little more time.
Hi @tolas123 , is it the same schema you've got than the one I attach? Seems to me I can read it and link to your picture, as far as I can see? I'm not certain since I can't read the components very well, but it looks like it, or am I wrong?
If necessary, I've got the same one for left analog circuit. Let me know.
If necessary, I've got the same one for left analog circuit. Let me know.