New 388 problem

Hm. Interesting. Stay tuned. I'm not sure but I think U104 might need replaced.

I'll have some more things to probe later.
 
Just FYI, I took off the nuts on the Monitor Pan channel strip so I could pull out the PCB BUSS B card a bit to get a better look.

We weren't crazy. Q101-104 are not listed on the PCB layout in the manual. In their spot (on the layout) is "U103," which looks like an IC on the layout. But there is no physical U103. In actuality, the four JFETs (Q101-104) are located where the layout says U103 should be.

Interestingly, in the Parts List (page 3-23 in the manual), there's no U103 mentioned, but Q101-104 are mentioned.

Sounds as though they must have made a parts change at some point and forgot to make adjustments to the manual maybe?
 
Yeah that happens. Makes sense...I was wondering where U103 was lol. Okay. Good to know. Good sleuthing. :)
 
Well duh...of course the result of step 3 (measuring the voltage between those BUSS B PCB) was 0 volts. Power comes from the MONITOR PCB to the BUSS B PCB via the M BUSS PCB (that goes for ALL the mixer channel cards by the way)...so with the M BUSS PCB removed there is no power to be had.

So at this point I'm thinking a couple options are:

1. Now that you know where Q101 is, go back a few posts and test for test tone at the S terminal of Q101 on the BUSS B PCB to confirm signal is getting to that point
2. Find a way to jumper power and ground from the MONITOR PCB to the BUSS B PCB so we can do step 3 of my last set of instructions
3. Say "screw it" and shotgun U104 on the BUSS B PCB (shotgun is the term used when you blindly replace a part you *think* might be the cause of a problem but you don't really know for sure) and put a new part in.

Think about any or all of those suggestions and I can help you with any/all of them.

Outside of that, reinstall the M BUSS PCB and let's check the following voltages at P102 of the BUSS B PCB:

1. Meter set to DC volts, measure between pin 5 and pin 8
2. Meter set to AC volts, measure between pin 5 and pin 8
3. Meter set to DC volts, measure between pin 6 and pin 8
4. Meter set to AC volts, measure between pin 6 and pin 8

Report back
 
sweetbeats said:
Well duh...of course the result of step 3 (measuring the voltage between those BUSS B PCB) was 0 volts. Power comes from the MONITOR PCB to the BUSS B PCB via the M BUSS PCB (that goes for ALL the mixer channel cards by the way)...so with the M BUSS PCB removed there is no power to be had.

So at this point I'm thinking a couple options are:

1. Now that you know where Q101 is, go back a few posts and test for test tone at the S terminal of Q101 on the BUSS B PCB to confirm signal is getting to that point
2. Find a way to jumper power and ground from the MONITOR PCB to the BUSS B PCB so we can do step 3 of my last set of instructions
3. Say "screw it" and shotgun U104 on the BUSS B PCB (shotgun is the term used when you blindly replace a part you *think* might be the cause of a problem but you don't really know for sure) and put a new part in.

Think about any or all of those suggestions and I can help you with any/all of them.

Outside of that, reinstall the M BUSS PCB and let's check the following voltages at P102 of the BUSS B PCB:

1. Meter set to DC volts, measure between pin 5 and pin 8
2. Meter set to AC volts, measure between pin 5 and pin 8
3. Meter set to DC volts, measure between pin 6 and pin 8
4. Meter set to AC volts, measure between pin 6 and pin 8

Report back
Click to expand...

Ok, I have the MONITOR BUSS PBC installed again (I realized that, way back, you had suggested to clean those contacts with DeOxit, and I had never done it. I did that, and it didn't solve the issue). So I'll check those last four voltages this evening and then decide which of the three options on top I'd like to try.

I think I can do #1.

I'm willing to do #2 if you can tell me how to do it. (I have jumper wires with alligator clips and such)

And after you first mentioned U104, I looked for the part and located it. I haven't bought anything yet, because I wanted to check with you to make I was buying the right type.

I think this is what I need, correct? It's the M14049B in a through-hole design. I've tried to determine what the "CP" stands for, but I can't find it anywhere. Do you know?

http://www.mouser.com/ProductDetail/ON-Semiconductor/MC14049BCP/?qs=g2rIOKKlpoZfkzib/e2WGQ==

Mouser doesn't have any in stock, but I found a few places that do:
mc14049bcp Stock and Price by Distributor
 
sweetbeats said:
Yes MC14049 through-hole 16-pin dip package.

Here's another source:

Motorola - MC14049UBCP - IC, CMOS. Hex buffer.

Ignore the CP. a lot of times those suffix letters are an identifier created by a common application, but there is no difference in the part itself.

Check those voltages, let me know.
Click to expand...

I was going to go ahead and buy from the link you supplied, but they wanted over $9 for shipping.

These work work, yes?

Motorola MC14049UBCP MC14049 Hex Inverter Buffer 16pin DIP Qty 5 | eBay

or

Motorola MC14049UBCP MC14049 Hex Inverter Buffer 16pin DIP Qty 5 | eBay
 
Good gracious...$9 to ship a 16-pin dip IC.

Both of your links were the same thing. Was that intended or was there another different link you meant to post?
 
And I'm an ignoramous. :D

I'd go with that last option. I know you get a smaller quantity for your money, but I am less concerned about non-genuine/counterfeit parts with that last option.
 
sweetbeats said:
And I'm an ignoramous. :D

I'd go with that last option. I know you get a smaller quantity for your money, but I am less concerned about non-genuine/counterfeit parts with that last option.
Click to expand...

Cool, will do. I'll go ahead and order them. Even if the problem turns out to be something else, I'll only be out a few bucks, and I'll have a few extra ICs floating around.

I haven't had a chance to measure the voltages yet ... maybe tonight. I'm working on a timely project right now, so my tinkering time has been little. I'll get to it as soon as I can, though.
 
sweetbeats said:
Well duh...of course the result of step 3 (measuring the voltage between those BUSS B PCB) was 0 volts. Power comes from the MONITOR PCB to the BUSS B PCB via the M BUSS PCB (that goes for ALL the mixer channel cards by the way)...so with the M BUSS PCB removed there is no power to be had.

So at this point I'm thinking a couple options are:

1. Now that you know where Q101 is, go back a few posts and test for test tone at the S terminal of Q101 on the BUSS B PCB to confirm signal is getting to that point
2. Find a way to jumper power and ground from the MONITOR PCB to the BUSS B PCB so we can do step 3 of my last set of instructions
3. Say "screw it" and shotgun U104 on the BUSS B PCB (shotgun is the term used when you blindly replace a part you *think* might be the cause of a problem but you don't really know for sure) and put a new part in.

Think about any or all of those suggestions and I can help you with any/all of them.

Outside of that, reinstall the M BUSS PCB and let's check the following voltages at P102 of the BUSS B PCB:

1. Meter set to DC volts, measure between pin 5 and pin 8
2. Meter set to AC volts, measure between pin 5 and pin 8
3. Meter set to DC volts, measure between pin 6 and pin 8
4. Meter set to AC volts, measure between pin 6 and pin 8

Report back
Click to expand...

Ok, I finally got to check those voltages in the bottom four steps listed above.

First of all, I wasn't able to, with the M BUSS PCB ASSY reinstalled, get direct access to the pins on the P102 connector. See photo "M BUSS side view."

Even if I took all the nuts off the front and pulled all the cards out, I don't know if I'd be able to measure the pins on the actual P102. So, I measured at the matching spots on the M BUSS ASSY. See photo "M BUSS and PCB ASSY B." I assumed that, since they were directly connected at those points, the measurements would be the same. Is that correct?

Here's what I got:

Pin 5 to Pin 8, DC = 15.16 V

Pin 6 to Pin 8, DC = 15.27 V

When I tried to make AC volt measurements, it would not stabilize. It just kept cycling through seemingly random numbers. You didn't specify a pos. and neg. probe, so I tried both ways and got the same results.

Do I need to adjust the range on the meter maybe?
 

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Measuring the pins from the M BUSS PCB is fine. Good logic/thinking there.

Those DC voltage results are fine.

Do you have AC volts range adjustments? I don't know what meter you are using. Mine auto-ranges so I didn't even think to ask. We're going to be measuring in the millivolts so set the range to whatever the smallest voltage is.
 
sweetbeats said:
Measuring the pins from the M BUSS PCB is fine. Good logic/thinking there.

Those DC voltage results are fine.

Do you have AC volts range adjustments? I don't know what meter you are using. Mine auto-ranges so I didn't even think to ask. We're going to be measuring in the millivolts so set the range to whatever the smallest voltage is.
Click to expand...

My meter is a Mastech MY68:
Mastech MY68 Series Handheld Digital Multimeter 33/4 Autorange

It's not total junk, but it's not a Fluke or anything.

It has an auto setting for volts, but it also has a range setting. I was just wondering if that was the issue because you had mentioned earlier that I might need to adjust the range setting when measuring resistance on something a few pages back.

I'll set it to mV and try again.
 
sweetbeats said:
Measuring the pins from the M BUSS PCB is fine. Good logic/thinking there.

Those DC voltage results are fine.

Do you have AC volts range adjustments? I don't know what meter you are using. Mine auto-ranges so I didn't even think to ask. We're going to be measuring in the millivolts so set the range to whatever the smallest voltage is.
Click to expand...

Ok, just tried again. With my meter set to mV for AC, I got 1.6 mV for pin 8 to pin 6.

For pin 8 to pin 5, I kept getting "OL" when I had it set for mV, so I set the range to single-digit volts, and I got .004 volts, or 4 mV. I don't know why it wouldn't just read it when I had it set to mV, but .... whatever.

I verified it twice.
 
Okay. That all seems fine.

The best way to look at power rails is with a scope, but you can also do some quick and dirty measurements with a DMM and catch major issues. Scope is nice because you can actually see the waveforms and verify they are clean and of proper form. But you've got the DMM...good enough here. The reason to set your meter to AC volts on a DC power is what? A DC power does. A couple things for us: rectifies the AC power at its input to DC, and regulates the output for proper amplitude. It also filters the power so it is clean and stable. So we had you check those pins for DC to make sure they were about +15 and -15 volts (and what you measured was typical and good enough), and then we had you measure for AC volts because...there shouldn't be any. If there is AC current present on a DC power rail something is wrong. Single digit mVAC is fine.

So next I need you to be able put the + probe on the "G" terminal of either Q101 or Q102 of the BUSS B PCB, and the - probe on that same pin 8 on the M BUSS PCB that corresponds to pin 8 of P102 on the BUSS B PCB and measure for DC volts with all L-R assign switches in the up or unlatched position, and then measure DC volts with any L-R assign switch latched or in the down position.

Does that make sense? And is that physically possible?

Did you order those MC14049 parts?
 
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