Mnats 1176 - can't change ratio

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JanusRec

Well-known member
Joined
Oct 25, 2008
Messages
66
Location
Berlin, Germany
Hello erverybody.

After hours of trying to fix my mnats 1176 I'm again prone to give up; so I hope you guys have some ideas what to check, to find the problems.

The facts:
It's a mnats 1176 rotary switch version.
When I switch ratios, I only get small changes in compression.
It does compress though: Sine wave output changes when adjusting the q-bias pot.
I checked all the voltages in the input and GR control amps - nothing unusual.
The unit used to work fine, before I upgradet the input sections from IC to transformer input.

What seems strange:
The ouput pot affects the feedback AC (at point 22). Is this normal - the wiper only connected to the ouputsection?
Switching to "Bypass" doesn't affect the compression/ output level. I checked all the swiched for shorts etc. - no problem there.

So if you any ideas - would be great.
And are there any additional things I can ckeck (resitances, AC voltages maybe)?

Thanks, Sebastian
 
Hi Sebastian,

These posts really belong in the 1176 thread. You will also find valuable info there.

http://www.groupdiy.com/index.php?topic=155

Mark
 
Yeas, I know the META but it's not possible to post anything there, right. Or did you refer to the repost-thread?

Anyway, new facts:

AC voltage in the ratio switch chandes properly, but the generated DC voltage at the gate of the FET does not (stays around - 1,5V), so there must be a problem in the control amp section...
 
From the 1176 thread:

JanusRec said:
Ok, I measured the AC voltages in the control amp section with a sine wave applied. The amplification is poor, so this is my problem. Probably one of the BC107s is blown. Any idea how to find out which one; the DC voltages are ok, as already wrote. Or is there another possible reason for the poor amplification; broken caps or so?

Does seem he posted after that, or at least there's just a lot of stuff going on in there. I know it's tough, but read through it. go to the thread and use the search function (the lower one, not the google one) and it will bring up results from that thread only.
 
JanusRec said:
When I switch ratios, I only get small changes in compression.

I shouldn't encourage you by replying to this thread, we have 1176 support threads for a reason!  Your solutions will help other people.

Anyhow - you are aware that as you change ratio the threshold on the 1176 goes higher?  That means that when you switch to a higher ratio you will not get more compression.
 
nhaudio said:
Hi Janus,

did you find an solution to your problem? I have the same issue.

cheers

Check the connections between the main pcb and the switch boards. I don't remember the exact one, but the was a loose connections in my case.
Cheers.
 

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