group card trouble

[christiancarvin]

Hello from France!

I'm trying to fix a problem with a group card: it gives me sound on the small fader corresponding to the group output targeted without subgroup button pushed and
without in and pre button pushed...I've already changed ne5534 group in and out, also ne5534 monitor and quad bus select. I've also changed the two fet (?) of small fader select: no result!
I've exchanged with a working group card and it works...
Any ideas?

Thanks!

[sintech]

Hi, you said you've changed two FET's  for the small fader select? The problem seems to be earlier than this.

So what I think your saying is.. without pressing the Ready Group button, you still hear the Group monitor input at the small fader.

Without Ready Group pressed, the signal shouldn't reach T5 which feeds the small fader select. If it does (which seems to be the case) we need to look before to: JFET RG5 as it shouldn't pass this relay.

That would be the first change.

[christiancarvin]

Thanks for reply!

I'm not sure that my explanation was good enough (sorry for that!)
Let's take an example: If I push the routing switch 32 on the module 12, I can ear sound in the small fader of the 32 module (without subgroup pushed and in/pre pushed on module 32). The problem is on the group card of module 32....

Sorry again for my English!

[sintech]

Yeah ok, so any channel routed to 32 on the matrix, will appear at small fader 32 with no buttons pressed on module 32?

If so, the audio to Matrix 32 will be present on the group card to JFET RG5, it should only pass that if ready group is pressed.

[christiancarvin]

Thanks a lot!
I'll try to change it this evening!

[christiancarvin]

Is there anyway to test a Jfet on the card?

[sintech]

Normally scope the signal path through the card to get an idea what is going on before changing any parts.

If you have an scope or a probe, you could compare against a good card.

The logic for the switching is good, as it's on a different card, so you have to look at the next thing in the chain.

[christiancarvin]

I've got an oscilloscope...I'll try....I'm really bad at reading schematics....
I've got to learn more on components specification I guess....
for example on this group card:
You would put extender on module 32...
and send a 1k tone in module 12 (for example) then route the signal on 32 with routing switch.
Then ear the problem on small fader of module 32...
then take the oscilloscope probe and put it just between RG5 and T5 and see if there is any signal that's right?
And if there's a signal without ready group pressed that would mean RG5 dead?

Thanks a lot for being my electronic teacher!

[sintech]

Hi, made a quick YouTube scoping the correct operation of the RG5 Fet.

http://youtu.be/JDMeW4OKzWs

Please note.. it's a cheapo 99 pound LCD scope, that can look a bit sea sick! at times.. but it's the perfect thing to fault find with

[christiancarvin]

You're amazing man!!
I'll try that!

[christiancarvin]

the test is done!
I have a small signal on pin 6 of IC5 without ready group pushed!
I'm going to change RG5 fet....Epic!

[christiancarvin]

I'm stocked!!!!
You were right This is perfectly working now!!!

[christiancarvin]

How can you follow the path of sound on schematics? It's magic!!!

[sintech]

Aha!! brilliant.

Thing is.. from your original description it had to be RG5 ..and nothing else in my mind, getting the scope out just confirms things.

In this case the block diagram is your friend, as it allows you to see the chain of events, in this case a very small one.