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Answer: Make sure you've calibrated your build first! After that, most problems are the result of one or more of the following conditions:
There is a lot of complexity to an 1176. Check your build carefully against the original schematic or the Hairball Build Guides. No drawing or wiring guide is completely foolproof and the original documents have been verified as correct (with the exception of R12 in the Rev D and related schematics).
You may be able to narrow down major issues to the troublesome section by checking voltages. Here is the Revision A V1.2.5 schematic with typical voltages added. Here's another for the Rev D/E and here's another schematic with voltages added from Jakob @ Gyraf for the Rev F and later.
Note that there is a voltage drop of approximately 0.6 V between the base and emitter of the bipolar transistors. Any voltages that are grossly different from the ones that appear in the schematic corresponding to the revision you're working on will point to the problem area. It may be a problem with the transistor itself or some other component, solder bridge, poor joint or mis-wiring as stated above. Test each component surrounding and including the transistor that gives the wrong voltage(s). Please note that I am not suggesting that you measure voltages and post them to the forum! If the voltages are wrong, you either have a faulty or incorrect component(s), component(s) inserted the wrong way, solder bridge or poor joint, mis-wiring, or you are simply measuring incorrectly.
If the fault appears to be in the audio path, you can trace the signal using Mark Burnley's DIY signal tracer hosted by DIY Factory. For other faults it can be useful to check typical voltages in the problem area and confirm them with a working unit.
If you are unable or unwilling to check the above, the next thing you can do is to use the search function at the Group DIY forum and see if someone has had a similar problem to yours.
If you're certain you have a unique problem that no one has resolved post a question to the appropriate section of the Group DIY Forum. The default thread for G1176 problems (mnats Rev J) is All things G1176 - the new "repost" thread. There is also a thread for the Rev A, a thread for the Rev D and another thread for the Rev F. Some kind soul will probably be able to help you out, and others may be able to benefit from your experience.
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A: Try this: pop the lid on your limiter, put the meter in GR mode and place a finger on Q12 in the GR Meter Driver Amplifier section. Watch the meter drift and observe the direction. Now place your finger on Q13 and observe the meter.
It should be clear by now that the GR meter is sensitive to temperature variations which is why the original (and the Hairball case) has a hole in the front to zero the meter. Allow your unit to come up to working temperature before zeroing the meter. The meter shouldn't drift much after warm-up unless there are external temperature variations that are affecting the unit or your printed circuit board around the FETs is contaminated with flux residue or other foreign substances.
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A: No. Try this: hook up the output of your unit to an oscilloscope while turning the output knob clockwise. Have a look at the waveform. Is the unit actually oscillating?
If so, check the wires coming from the output transformer to the VU meter and ensure that they run along the inside edges and corners of the case rather than dangle precipitously across the main PCB. Note that these wires should be routed far from the signal preamp circuit on the main PCB or there is a chance that feedback between the output and input circuits will occur.
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Answer: The components marked * on the Rev J board are optional components not included in the original unit or schematic. If you are using the Lundahl LL1540 input transformer, you need to use two 10k resistors in the places marked R* and R*1 and feed the input level potentiometer from the pad marked *1.
The values for the other optional components are listed on Jakob's PDF located at http://www.gyraf.dk/gy_pd/1176/1176.pdf. As the components marked * are not part of the original unit you do not have to use them in order to get a working clone. Some of my very early boards had a component marked C*4. This is actually supposed to be C35 and should be included on the board. The value is listed on the BOM.
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A: From the schematic or screen layer of my boards: IC 2; R1-A, B, C, D, E; R3; R4; C*4 (C35); C30; C31; C32; C33; C34; C100; C101. On the newer Rev J boards these components are contained within a line border to facilitate their identification.
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