Does anyone have a schematic for a Crate PA-B6350 (6-channel mixer) or PA-B8350 (8-channel). Power amp section works fine, but -15vdc on preamp board is only -7v. The +15vdc is fine. I have pulled all the opamps, but still no -15vdc.
Follow the -15V trace backwards, towards the power supply.
You may pass through a connector and some wire, check if tiu have your -15V "on the other side"
Keep following the corresponding tracks, you'll probably get to a 3 leg "transistor" which actually is a voltage regulator.
Measure and post voltage on all 3 pins, together with a simple sketch of its case and pins, for clarity.
I am pretty sure I found the trouble. One of the two 16v zeners was running at only 7 volts. The other one was fine. I will know for sure when I get a replacement zener. Thanks to all.
Quote from: steelguy on December 30, 2010, 03:19:10 PM
I am pretty sure I found the trouble. One of the two 16v zeners was running at only 7 volts. The other one was fine. I will know for sure when I get a replacement zener. Thanks to all.
Ah, that would definitely do it. Let us know if that fixes your issue.
The zener fixed the problem. Now if I could find some 70-503-41 replacement pots. I have two with broken shafts.
Quote70-503-41 replacement pots.
That's most certainly an internal warehouse/inventory code.
Maybe they have the actual ohms value printed somewhere (sometimes even on the front pot side, invisible because it touches the front panel).
Post any code you find on them, maybe the value is screen printed on the board itself, *or, if they suffer only from broken shafts and nothing else, pull them (carefully) and measure them with a multimeter.
If only a couple of them, you can replace them with any regualar pot, which has same pin separation, which implies same diameter, and, obviously, same value.
*Maybe* the replacement will lack some mounting fins, pins or frame which hold it securely to the board, but one or two won't weaken that too much.
Of course, you may go to the source and contact Crate themselves.
Thumbing through some mail-order catalogs won't hurt either.
Post a couple pictures and good luck.
70-503-41 is the complete part number. MOST Crate pots have the resistance as th center grouping, read like colors, so 50k here. But you cannopt rely on that, other than that I looked it up
If your resistor stripe is OK, you can reassemble a new shaft into it from any other pot in that series.
Quote from: steelguy on December 29, 2010, 09:07:22 PM
Does anyone have a schematic for a Crate PA-B6350 (6-channel mixer) or PA-B8350 (8-channel). Power amp section works fine, but -15vdc on preamp board is only -7v. The +15vdc is fine. I have pulled all the opamps, but still no -15vdc.
Yes, someone had a schematic. I needed one and found it somewhere (in two files). I thought I would post them here (although this is very old) because this thread comes up on a Google search for this schematic.
My PA-B6350 had the output cutting in and out (sold to me that way, cheap), and I found that merely the "Main Out"/"Eq In" shorting type 1/4" jacks were dirty (still are, I just put a Tip/Ring 1/4" jumper in; back, back, back burner to fix).
Phil in beautiful Talking Rock, Georgia, USA