C4S installation troubleshooting

[grosen]

I

[mchurch]

Hi;

I won't profess to be an expert here but one thing I noticed in my build was to make sure the right transistor is in the right location and that they are not down flush with the board as the metal can might short out the traces. Also verify that the wires connected to the board are intact. When I was stripping the wires I inadvertently pinched one of the wires and although it appeared well soldered it broke while I was performing the checks. The other thing to watch out for is overheating the transistors while soldering. This can lead to issues further on in time.

Someone else on this forum suggested taking readings across the legs of the transistors to see if any are open which would indicate the transistor is cooked. I am sure there will be others who can weigh in with more advice, these are just my initial thoughts.

If it was working well before the upgrade I am sure it is something that can be resolved.



Cheers

Mike

[Doc B.]

Actually a bad transistor usually reads shorted, not open. Did you perhaps short two traces together when you were taking measurements? That could create the sudden darkening of the LEDs as something got too much current and died.

I agree that checking all of the semiconductors is probably worthwhile. Anything that reads shorted across the pins is dead.

[grosen]

Thanks for the amazingly quick responses.  The transistors do not appear to be shorted out, and the wires to the board look ok.  I'm not sure how to test the LEDs, but two of the LEDs on the board seem to be passing current in one direction but not the other, while the other two test as open in both directions.   Could that be it?

[Doc B.]

One LED in each pair will sometimes light when you use the meter, and the other in that string won't. Is it one LED in each series pair that reads open, or are both LEDs in one string reading open?

As mentioned before, check to see if the metal cans of the 2N2907 transistors are touching the traces.

[grosen]

Hmm...  Now all of the LEDs are reading open.  (Before it was just one in each string.)  The transistor cans are not touching the traces.

[Doc B.]

Check each of your transistors for shorts by measuring resistance across each of the three possible combinations of two leads. Everything should be reading from about 1.5K ohms up to infinity. If anything reads low like 200 ohms or less that is a dead transistor.

[Paul Joppa]

From the description, it seems the tubes are not lighting up. First check is, are they installed?  :^)  stranger things have happened - to me = ...  If the tubes are missing, or the wiring to the heaters has become disconnected, then the heater power supply capacitor won't discharge, causing odd behavior when measuring resistance.

[grosen]

YES!  We're back in business.  Paul was right.  The wiring to the heaters had become disconnected -- don't know how.  Anyway, all is well.  FWIW, the C4S has done just what I hoped it would do.  I'm running a Dynavector 10x5.  It was a bit of a challenge for the stock seduction (compared to my Shure V15 IV), but it's just right with the C4S.  Many thanks for the help.  (Next stop, Eros.)