I was working on some 1176LN Rev D's with meter issues and a web search led me to this thread. (Actually, the thread helped me to work out my procedure.) Regarding R44 and the meter calibration steps, here's how I align this circuit on Rev D's. I don't add trimpots to original units but you can bypass the last step by using a 10k trimpot for R44. The FET is critical.
Let the unit warm up for at least a half hour. After setting the Q1 bias and verifying that audio limiting is working ok, measure the output level with an external meter, select GR metering, and select 20:1 ratio. Connect a 10K pot or a resistor sub box, set to 3K, to the Q12 and Q13 emitters (R44 pads, with no R44 connected yet). Apply a 1K sine wave to the input (+4 is fine but input level is not critical) and adjust the input and output controls so that when you turn the attack on, output level decreases by 10 db.
Turn attack off. Connect a DVM (range of 2-5 VDC is good) to R74. Adjust R75 (Null) for zero volts. Adjust R71 (GR zero) for zero on the VU meter. The adjustments interact so you might have to repeat them 2 or 3 times.
After that is done, turn the attack switch back on. The GR meter reading should go down. Change the setting on the test pot or sub box to achieve a reading of -10 on the VU meter. Double check your external meter to be sure you still have a 10 db change. Toggle the attack switch on/off a few times to verify zero and -10 on the meter. (With attack and release set to fast this part will be quicker.)
Turn off the attack, and re-check the voltage across R75. If it's not zero, re tune the trimmers as needed. Check R44 again, you may have to adjust it one more time for an exact 10 db change.
Disconnect the pot or sub box and check the resistance. If using a test pot, you'll use your DVM to carefully measure it's resistance at that setting. Choose a resistor or (if you don't have a Wall Of Resistance like the one on our web site http://studioelectronics.biz/MeetTheShop8-13.html) combine resistors to match the value that you measured. Temp in the resistor(s) and if you still have -10 on the meter, solder it in and you are done.
[quote author="ap123"]Upon actually following the calibration procedures outlined in the urei docs I encountered a never-ending circle of confusion. For instance, the more I tinker I realize that the procedure outlined in 5.3.2 is sort of dependent on that of 5.3.3 and so on.
Does the procedure to adjust the null and tracking require the complete removal of R44? On page 60 of the urei pdf, there is a document entitled "Meter Calibration" the relationship between R75, R71, and R44...that is a sensitive dynamic that one there, especially when you throw the R44 as a trim pot into the mix.
Also, I read in the G thread that shorting terminal 22 to ground is the same as placing attack in the off position (as mentioned numerous times in the docs). Does this apply to the rev D board?
Can the bias adjustment be made with the meter trim pots whacked out (or centered, say)?
I need to finish reading the rev G thread one of these days...sorry.[/quote]
