modded 1176s

roly · 26th June 2006

Hi folks
I have 2 1176s that have been modded for broadcast.
I need to get them back to stock.
I can post pictures.
Anyone here willing to PM me with help/advice?
cheers
Roly

David Kulka · 26th June 2006

I've worked on a lot of 1176's but it's hard to say what your "broadcast" mod might include. Maybe it's just a simple stereo link, or EQ might have added to the gain reduction circuit. Maybe HF emphasis for FM radio?

In any case, the goal is to make them match the schematic again. First, identify the version -- are they LN's, and what are the serial numbers? The serial numbers will lead you to the correct schematic. I think they are all on the JBL site, if you don't have a schematic.

With the schematic at hand and the unit opened up in front of you, it should be fairly easy to spot parts that have been changed or added. The appearance of the solder connections on the bottom may tell you what has been changed.

If the visual clues aren't enough, and you have no docs on the mod, someone will need to inspect the top of and bottom of the circuit board looking for parts that don't match the drawing, stuff that's been added or removed, jumper wires, cut foils, etc.

Although this may sound complicated, chances are the mod is quite simple and will be fairly easy to spot and undo. With any luck it will just involve a few parts.

If the units have never been recapped, now is the time. All the electrolytics should be replaced, to insure that the sonics match the original specs. If they aren't, it may be hard to evaluate your mod removal since the old caps might be creating unintended sonic changes of their own.

roly · 27th June 2006

Hi David
Thanks for your help.
They are revision F units. I was told that the attack and release pots have been disabled and replaced with resistors and that a high frequency emphasis mod has been done to them. One looks like it has the hi freq mod with a bypass switch on the back of the chassis, the other one does not apear to have similar changes, bypasable or otherwise.
One has a smoked resistor -R84, with lots of heat signs on the board.
There is a jumper wire from the full clockwise position of the release pot to the fcw position of the attack pot.
There is a 276K resistor across the center to the fcc connector of the release pot on one unit. The other one has the same value resistor across the fcw fccw of the release pot.????
On one attack pot the centre to full clockwise tabs are jumped with a resistor and cap in parallel. On the other the same thing but between the ccw/ cw connectors.????
I know this is a prety primative description and the spelling is lousy but I hope there is enough information for you to make sence of things.
cheers
Roly

26th June 2006	#1
roly Gear Head Join Date: Dec 2003 Posts: 38 Thread Starter	modded 1176s Hi folks I have 2 1176s that have been modded for broadcast. I need to get them back to stock. I can post pictures. Anyone here willing to PM me with help/advice? cheers Roly

26th June 2006	#2
David Kulka Lives for gear Join Date: Oct 2004 Location: Burbank, CA, USA Posts: 1,026	I've worked on a lot of 1176's but it's hard to say what your "broadcast" mod might include. Maybe it's just a simple stereo link, or EQ might have added to the gain reduction circuit. Maybe HF emphasis for FM radio? In any case, the goal is to make them match the schematic again. First, identify the version -- are they LN's, and what are the serial numbers? The serial numbers will lead you to the correct schematic. I think they are all on the JBL site, if you don't have a schematic. With the schematic at hand and the unit opened up in front of you, it should be fairly easy to spot parts that have been changed or added. The appearance of the solder connections on the bottom may tell you what has been changed. If the visual clues aren't enough, and you have no docs on the mod, someone will need to inspect the top of and bottom of the circuit board looking for parts that don't match the drawing, stuff that's been added or removed, jumper wires, cut foils, etc. Although this may sound complicated, chances are the mod is quite simple and will be fairly easy to spot and undo. With any luck it will just involve a few parts. If the units have never been recapped, now is the time. All the electrolytics should be replaced, to insure that the sonics match the original specs. If they aren't, it may be hard to evaluate your mod removal since the old caps might be creating unintended sonic changes of their own. __________________ http://studioelectronics.biz Service & Restoration of UREI dbx Eventide Marshall AMS Tube Gear and more

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27th June 2006	#3
roly Gear Head Join Date: Dec 2003 Posts: 38 Thread Starter	Hi David Thanks for your help. They are revision F units. I was told that the attack and release pots have been disabled and replaced with resistors and that a high frequency emphasis mod has been done to them. One looks like it has the hi freq mod with a bypass switch on the back of the chassis, the other one does not apear to have similar changes, bypasable or otherwise. One has a smoked resistor -R84, with lots of heat signs on the board. There is a jumper wire from the full clockwise position of the release pot to the fcw position of the attack pot. There is a 276K resistor across the center to the fcc connector of the release pot on one unit. The other one has the same value resistor across the fcw fccw of the release pot.???? On one attack pot the centre to full clockwise tabs are jumped with a resistor and cap in parallel. On the other the same thing but between the ccw/ cw connectors.???? I know this is a prety primative description and the spelling is lousy but I hope there is enough information for you to make sence of things. cheers Roly