Optimod 8000A G/R metering. .

[mattthepm]

Just received an Optimod 8000A today for our LPFM station and noticed the gain reduction metering section does not work. All other positions (L IN, R IN, etc) work OK.

Wondering where I need to look, whether it be on the limiter board or in the meter selector switch itself?

Thanks,

-M

 

[LA_Guy]

It probably has a bad release time module. I'd give Bill Sacks a call: www.optimod.fm

 

[DaveBayArea]

We have an 8000 that's doing the same thing, only it seems to be heat related. I take the lid off, and it works fine. Put it back on, and the G/R goes way down after about 1/2 hour. Some testing with a heat gun shows that this module - the 30075 - or something near it is the culprit. The manual has an adjustment called "FET bias" that controls the voltage to one pin of this module, but I can't find any other info on it or a schematic of what's inside. Does anyone have any info on what this is, what it does, or what to look for on the pin-outs? I'll start looking further on Monday when businesses open, but I'd like to get this running before then if possible. There's also quite a few Tantalum capacitors in the area and I've learned to be suspicious of them too.

Any insight you can provide would be greatly appreciated.

Dave B.

 

[Bill Sacks]

We have an 8000 that's doing the same thing, only it seems to be heat related. I take the lid off, and it works fine. Put it back on, and the G/R goes way down after about 1/2 hour. Some testing with a heat gun shows that this module - the 30075 - or something near it is the culprit. The manual has an adjustment called "FET bias" that controls the voltage to one pin of this module, but I can't find any other info on it or a schematic of what's inside. Does anyone have any info on what this is, what it does, or what to look for on the pin-outs? I'll start looking further on Monday when businesses open, but I'd like to get this running before then if possible. There's also quite a few Tantalum capacitors in the area and I've learned to be suspicious of them too.

Any insight you can provide would be greatly appreciated.

Dave B.

The magic inside of the 8000A's release time module is still to this day a closely held trade secret.
We have been entrusted by Bob Orban to make exact replacement potted modules from the original prints for repairing 8000A's.
I think the issue might be a maladjusted FET bias control and not the module itself. The heat gun is likely also heating up the FETS and changing their operating point. The manual has a well written procedure for adjusting this FET bias with a tone burst. This adjustment is critical and must be done precisely as shown to produce the exact envelope on the scope as pictured in the manual, before suspecting the release time module.
Here is what an 8000A can sound like when lovingly refurbished and rechipped/recapped
http://www.youtube.com/watch?v=PNbTv7Gn3ww&feature=channel_page
Feel free to contact me directly for further help with your 8000A.