[Mikeyod]

My Studer A810 Is popping when switching between Input (Inp.) and Rep. on the right channel.
When I swap the line amplifier cards (1.820.714) the pop follows the card.
I swapped the LM393, 5532 and the MM74C374N op amps between the two cards and the pop stuck with the original card.
             It looks like the switching takes place between the 374 , LM393 and the SD211 are these  SD211 the likely culprit. I hope not as they seem hard to find.

[radardoug]

Any caps in the signal path? Thats a likely culprit.

[Mikeyod]

When I first got the machine I recapped all the electrolytic caps( and all the RIFAs) the only other ones on the board are solid aluminum or ceramic. I haven't ever seen any of them go. Have you experienced any problems with them?

[radardoug]

Solid alis are usually pretty good. But the click will be a d.c.offset somewhere. Could be a switch chip. The best way is put it on an extender card and follow the audio path with a scope. The 810s etc used Analog Devices Multiplying Dacs quite a bit, could be one of those?

[radardoug]

Downloaded the manual. Looks like those fet switches could be suspect, but first check the dip switch settings. Some of the switch combinations have conflicts.

[Mikeyod]

Oh yeah, I also removed those damn dip switches and put in jumpers. Those things caused more trouble than they are worth.
         I did just notice I missed that 100uf (C12) cap under the heat sink for the two transistors. I'll change that, it's in the signal path.

[Mikeyod]

Well it wasn't that cap. So I found some SD211DE on ebay waiting on them I suppose.
I'm thinking it should be either IC5 or IC7 as it looks like CA-DATA4 switches between the inputs.

Am I looking at that correctly ?

And thanks to Doug Jane for taking the time !!!!  It is appreciated !

[radardoug]

Its very complex, hard to look at the drawing on the computer and take all of it in. The left two fets look like they mute the line amp. So the right two do the input changeover. I would suggest scoping those outputs from the fets to see where there are d.c. shifts. You will still probably have to change at least two before you get it right, by Murphys law!

[radardoug]

Is your board modded per the asterisks to the .81 version? Are those 100ks there?

[Mikeyod]

Yes that was what I was thinking probably both Ic5 & 7 maybe I'll change 7 first. No, Murphy will be one up on me no matter what I do.     ; 0)

     Yes my boards have the .81 updates.

[Mikeyod]

Murphy is really getting a good laugh out of me lately.
After changing IC 5,6,7,8 in order ......    it still pops !
I swapped the card over from channel 2 to channel 1 just to check if I was crazy and it followed the card and now it pops the left speaker. New LM393 IC s did nothing. new MM74C374N IC nothing. R22 tested funky in circuit but was fine out at 22k. Put in new anyway no change.
Unfortunately I have no extender card so very difficult to check with scope.

[radardoug]

Its the sort of thing that an extender card will make much easier. An alternative is to solder a bunch of wires to appropriate points, so you can get the scope on to them. Once you find the source of the d.c. offset, you can go from there.

[Mikeyod]

O.K. thanks to Geoff Doane of this forum. I am now the proud owner of an A810 extender card !
( A80 VU extenders still a DREAM !!! )
However, I don't understand how to trace the PoP to a specific component ? I can see the normal switching on the scope and have compared it to the good card. But, I can see the PoP in any number of places on the bad card which is the result of the bad component. I was hoping this would be an opportunity for me to learn how to zero in on the failed component and not have to use trial and error and best guess method as in the past. Any advice greatly appreciated.
And one more shout out to Geoff thank you !

Mike

[Mikeyod]

Turned out to be C16. Nothing wrong with the capacitor. C16 makes no connection on the solder side of the circuit board only on the component side. However, little to no solder got through when they soldered originally at Studer. In looking at the aluminum caps on the board most were this way. Although some have different combinations of top vs. bottom connections so on some it doesn't matter. Just reheating and pushing some solder through made the connection and the pop is gone.      New motto

Half of troubleshooting is luck. The other half is keep trying until you get lucky.

Mike