New 388 problem

Now, leaving all other settings the same as you had it in your test above (including leaving the L-R assign switch latched on your input channel), connect a line source to the STEREO BUSS IN jacks.

Where do you hear the source?

• Headphones [ X ]YES [ ]NO
• STEREO OUT jacks [ X ]YES [ ]NO
• MONITOR OUT jacks [ X ]YES [ ]NO But, it's again about half the level of the STEREO OUT jacks when the MONITOR/PHONES dial is at about 50%. With that dial at 100%, the signal from the MONITOR OUT jacks is a little louder than the STEREO OUT jacks.

NOW, unlatch the L-R assign switch (so ALL assign switches are in the up/unlatched position).

Where do you hear the source?

• Headphones [ ]YES [ ]NO
• STEREO OUT jacks [ ]YES [ ]NO
• MONITOR OUT jacks [ ]YES [ ]NO
Same results as above

See my embedded reply above.
 
PRGRM BUSS inputs are post mixer.Think of the 388 as a 8 track-8x8- mixer feeding a 8 track recorder with the 8 PGRM BUSS inputs being summed with the 8 outputs of the mixer feeding the recorder.
 
1. Tip the 388 on its side and remove the bottom panel. Situate the unit so it is stable but so you also have clear access to the guts behind the bottom panel while still having access to the control surface.
2. Input a 1kHz test tone into any line input, assign it to the PGM 1 buss, and, making sure the PGM/CUE control is in the "PGM" position, adjust levels until the PGM 1 meter displays 0 VU
3. Adjust the MONITOR mixer channel 1 gain to the 2:00 position, PAN hard L
4. Set your multimeter to AC volts, and locate connectors P103 and P106 on the BUSS B PCB. The BUSS B PCB is the one with all the MONITOR mixer PAN controls. P103 is an 8-pin red connector. P106 is a 3-pin white connector. Put your + probe on pin 1 of P103. Put your - probe on pin 2 of P106.

Report what the meter reads. I'm hoping it is something around 200-300mV

We are starting to hunt down where signal breaks in the pathway to the monitor and headphone jacks. The PGM meters get their signal just after the MONITOR buffer amp that drives the MONITOR GAIN and PAN controls, but before the MONITOR GAIN control. If you want to see this in simplified version just look at the Block Diagram. Because the PGM meters show signal (and also because signals assigned to the PGM busses make it to tape), we know the MONITOR buffer amps are working. So I'm somewhat arbitrarily having you start the hunt for signal at a point just after the MONITOR GAIN control but before the MONITOR PAN control. You can look at the schematics for the BUSS A and BUSS B PCBs to see these controls and the interconnections. If there is signal there then I'm going to have you probe between the next logical point downstream after the PAN controls. There are IC logic switching circuits in the 388 that auto-switch the source depending on the position of any of the L-R assign switches. There are transistors on the BUSS B PCB that source the L-R buss depending on voltage control signal. If there is something wrong with that voltage control, it is possible the source of the headphones and MONITOR OUT jacks is always stuck on the L-R buss even when nothing is assigned to it.

Do the above steps and report back.
 
PRGRM BUSS inputs are post mixer.Think of the 388 as a 8 track-8x8- mixer feeding a 8 track recorder with the 8 PGRM BUSS inputs being summed with the 8 outputs of the mixer feeding the recorder.

Right, I can see that in the pictogram at the end of the owner's manual. Thanks for the tip! :)
 
1. Tip the 388 on its side and remove the bottom panel. Situate the unit so it is stable but so you also have clear access to the guts behind the bottom panel while still having access to the control surface.
2. Input a 1kHz test tone into any line input, assign it to the PGM 1 buss, and, making sure the PGM/CUE control is in the "PGM" position, adjust levels until the PGM 1 meter displays 0 VU
3. Adjust the MONITOR mixer channel 1 gain to the 2:00 position, PAN hard L
4. Set your multimeter to AC volts, and locate connectors P103 and P106 on the BUSS B PCB. The BUSS B PCB is the one with all the MONITOR mixer PAN controls. P103 is an 8-pin red connector. P106 is a 3-pin white connector. Put your + probe on pin 1 of P103. Put your - probe on pin 2 of P106.

Report what the meter reads. I'm hoping it is something around 200-300mV

We are starting to hunt down where signal breaks in the pathway to the monitor and headphone jacks. The PGM meters get their signal just after the MONITOR buffer amp that drives the MONITOR GAIN and PAN controls, but before the MONITOR GAIN control. If you want to see this in simplified version just look at the Block Diagram. Because the PGM meters show signal (and also because signals assigned to the PGM busses make it to tape), we know the MONITOR buffer amps are working. So I'm somewhat arbitrarily having you start the hunt for signal at a point just after the MONITOR GAIN control but before the MONITOR PAN control. You can look at the schematics for the BUSS A and BUSS B PCBs to see these controls and the interconnections. If there is signal there then I'm going to have you probe between the next logical point downstream after the PAN controls. There are IC logic switching circuits in the 388 that auto-switch the source depending on the position of any of the L-R assign switches. There are transistors on the BUSS B PCB that source the L-R buss depending on voltage control signal. If there is something wrong with that voltage control, it is possible the source of the headphones and MONITOR OUT jacks is always stuck on the L-R buss even when nothing is assigned to it.

Do the above steps and report back.

Ok great, thanks! I'll have to do this this evening. I'll report back tonight.
 
Please help me!!! Playback in headphones sound distorted and low

Im using garageband and a scarlett focusrite 2i4 audio interface..For some reason the playback in my headphones sound distorted and low..Ive replaced the headphones and also replaced the 1/4"inch to 1/8in inch adapter.. Also it plays perfectly fine from my monitors!! Only problem is my headphones sound like crap.. does it have anything to do with the buffering
 
Im using garageband and a scarlett focusrite 2i4 audio interface..For some reason the playback in my headphones sound distorted and low..Ive replaced the headphones and also replaced the 1/4"inch to 1/8in inch adapter.. Also it plays perfectly fine from my monitors!! Only problem is my headphones sound like crap.. does it have anything to do with the buffering

You should post this in the digital recording forum:)
 
Ok Cory, forgive my ignorance, but was I supposed to pull out those two connectors (P103 and P106) to make the measurement? I couldn't find a way to do it without pulling the connectors, so that's what I did.

I measured it three times and got the same result: .003 volts, aka 3 mV.

If I'm supposed to measure it while leaving those connectors in, please tell me how I can reach those pins. :) Do I need to take off all the knobs, faders, and nuts from the front and pull the whole channel assembly away?

Thanks
 
Ok Cory, forgive my ignorance, but was I supposed to pull out those two connectors (P103 and P106) to make the measurement? I couldn't find a way to do it without pulling the connectors, so that's what I did.

I measured it three times and got the same result: .003 volts, aka 3 mV.

If I'm supposed to measure it while leaving those connectors in, please tell me how I can reach those pins. :) Do I need to take off all the knobs, faders, and nuts from the front and pull the whole channel assembly away?

Thanks

After posting the above, I realized that I could touch the pins sticking through the other side of the PCB while the connectors were still in (still a bit new to this PCB probing business!), so I did that.

The measurement with the connectors plugged in was 60 mV. I confirmed three times.
 
Good job figuring out how to probe the pins with the connectors connected. There will be some of that figuring you'll have to do since I dont have a 388 to refer to. If you get in a real pickle just say so and we'll figure out a solution, but I'm going to be lobbing out "do [such and such]" with reckless disregard as to whether or not it is physically possible until you tell me otherwise and then we'll develop plan B. Make sense?
 
Cory
Just want to say on behalf of myself, but I think I speak for others as well, thank you.
You are always willing to help people with their troubleshooting needs. And it's not just general help but very specific stuff.

So, knowing that you have a life, and knowing that like anyone else you have your own issues and obstacles to deal with, the fact you'd give such thorough and detailed assistance is above and beyond.
So thank you!!!
(Just in case your contribution isn't recognised)
:D
 
Cory
Just want to say on behalf of myself, but I think I speak for others as well, thank you.
You are always willing to help people with their troubleshooting needs. And it's not just general help but very specific stuff.

So, knowing that you have a life, and knowing that like anyone else you have your own issues and obstacles to deal with, the fact you'd give such thorough and detailed assistance is above and beyond.
So thank you!!!
(Just in case your contribution isn't recognised)
:D

Absolutely. He's always going above and beyond the call of duty. It's not a stretch at all to say he's one of the greatest assets this forum has ever had.
 
Does that amount fluctuate when you adjust the position of the gain knob?

I'm assuming you're talking about the gain knob on the MONITOR mixer, so that's what I adjusted.

And yes it does. With the gain knob up all the way ("to 11"), I'm getting 330mV.
 
Thanks for the nice words fellas.

I really enjoy helping. Wish I could make a living at it, or at least had more time to do it. Maybe I'd work on some of my own projects if I cut back lol! :D

But many people much smarter than me have made similar if not much greater efforts many times when I needed help...it's a big part of why I have some knowledge and can help others. And so it goes. :)
 
I'm assuming you're talking about the gain knob on the MONITOR mixer, so that's what I adjusted.

And yes it does. With the gain knob up all the way ("to 11"), I'm getting 330mV.

Yes I meant monitor gain knob...very good question, and a good reminder. It's really important when troubleshootin remotely like this to be very specific. Things can get sideways quick! :drunk:

Good deal on the results of your follow up test.

On to the next test.

1. With 1kHz test tone still connected as in the last test, set the MONITOR mixer channel 1 GAIN control to 2:00ish, and the PAN control hard L
2. Find connector P108 on the BUSS B PCB; P108 should be a red 3-pin connector
3. With your multimeter still set to AC volts, measure between pins 1 & 2 of P108

What do you get?

P108 is a point in the signal path *after* the monitor mixer pan controls, and also after those auto-switching transistors I mentioned in a previous post related to the L-R buss. We are continuing downstream to discover where our test tone is no more.
 
Yes I meant monitor gain knob...very good question, and a good reminder. It's really important when troubleshootin remotely like this to be very specific. Things can get sideways quick! :drunk:

Good deal on the results of your follow up test.

On to the next test.

1. With 1kHz test tone still connected as in the last test, set the MONITOR mixer channel 1 GAIN control to 2:00ish, and the PAN control hard L
2. Find connector P108 on the BUSS B PCB; P108 should be a red 3-pin connector
3. With your multimeter still set to AC volts, measure between pins 1 & 2 of P108

What do you get?

P108 is a point in the signal path *after* the monitor mixer pan controls, and also after those auto-switching transistors I mentioned in a previous post related to the L-R buss. We are continuing downstream to discover where our test tone is no more.

Ok. You didn't specify which was pos and neg on the meter, so I tried it both ways. I got the same result either way: 3mV.

I then turned the monitor GAIN up full and still got the same measurement.
 
I figured as much.

Okay. So next we need to move upstream one step and see if we have signal at the input of the switching transistors. This may get tricky with just standard probes because I can't see how easy it is to get to the transistors.

You are looking for Q101 on the BUSS B PCB. It is a little JFET transistor. It'll have 3 legs and the legs should be labeled D, S and G on the board. Leaving all conditions the same as the previous test, I want you to put the + probe on the 'S' terminal of Q101, and leave the - probe on pin 2 of P108.

What do you get on the multimeter?

-OR-, put up a pic of what you are working with if you can't get to stuff, and we'll see if we can ascertain a work-around.

This is a JFET:

image.jpeg
 
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