Crackling TASCAM 388 AUX & EFF buss

M

mr.blisset

New member
Hi there,

This is my first post here so just thought i'd say great community you guys have going here, very glad to have found you all! :thumbs up:

So I've had some noise issues with my Tascam 388 for a while now. It doesn't print the noise to tape so I haven't really bothered finding out exactly what is up with it.

The noise also only starts to happen after the machine has warmed up a little.


Here's my trouble shooting so far:


I plugged a monitor into each out on the back of the 388 to try and determine which section of the unit the faulty component is a part of.

Firstly, I get NO NOISE from any of the channel strips themselves.


I plugged the monitor into the EFF OUT and AUX - I get hiss and the offending crackling noise.

Turning MASTER AUX and EFF down removes the noise.

Toggling the MON switch will worsen the crackling noises or if the noise is not already present then toggling this switch will 'activate' the noise so to speak.

The crackling noise is nearly always present with MON latched

Turning up the individual blue EFF knobs seem to make no difference. The crackling noise doesn't change.

If MON is not latched it will eventually quieten down or even go away completely for a short period, if I latch the MON then the noise will start up again immediately.



Does anyone here know why this is occurring in such a way or have any ideas on how to further trouble shoot this issue? thanks!
 
Hi and welcome.

So I have a few questions to make sure I am understanding your troubleshooting results. Thanks for the detail you provided already.

I'm going to number my questions so we don't confuse each other. Please number your responses according to the numbering of my questions. Your answers will help me pinpoint from where the problem likely originates. Be specific with your answers as much as you can.

1. Please verify the noise is present at BOTH the AUX and EFF master out jacks, and please verify it is both the RCA and 1/4" outs.

2. When you say the crackling noise is almost always present with MON latched:

A. which monitor switch is latched? STEREO? AUX? EFF?

B. And the noise is present where?

• STEREO OUT jacks yes or no?
• MONITOR OUT jacks yes or no?
 
Hey thanks for the help! I'll do my best answer your questions.


1. The crackling sound is present when plugging the monitor into both the AUX and EFF outputs (both RCA and 1/4").

2a. The MON switch that is latched is the PGM/CUE (blue) switch.

2a. The noise is also present when plugging the monitor into both the stereo out jacks and the monitor out jacks.


When I first turn on the machine the noise is not present. It only starts to occur once it has warmed up a bit I think.

The MON (PGM/CUE) switch makes a noise when I latch it on or off from the moment I turn the 388 on (like the sound you get when you touch the end of a guitar jack that's plugged into an amp). I'm not sure if this is normal?
The INSERT (on/off) switch also makes a similar noise but quieter.
When the machine is cold, these switches (although they make the sound I described above as I latch them) seem to function normally and do not trigger the crackling sound. However, once the machine has warmed up, the MON (PGM/CUE) switch seems to be related to the the crackling noise. As I latch it on and off the noise seems to change, start and stop as I do so.


The only other information I have for you is that today, once the machine had warmed up I got the familiar crackling sound but I also got some almost 'windy' sounds too. Maybe this helps?

Thanks again for responding sweetbeats!
 
so does it make any difference which of the STEREO, AUX, or EFF switches is latched over by the MONITOR/PHONES level control?
 
so to be clear, I'm using headphones to monitor the noise through via the monitor/phones outputs here.

If i have the STEREO latched to the MONITOR/PHONES section, I hear no noise when L/R is not latched on the channel strips.
When I latch L/R on the channels I can hear the noise. Turning down the individual green and blue AUX and EFF knobs on the channel and also the MASTER AUX/EFF knobs do not reduce the noise.
If I latch the MONO button on the STEREO MASTER channel I do get a noticeable rise in the noise floor.
Unlatching the L/R on the channels again I can longer hear any noise in my headphones. I still get a rise floor when latching the MONO

If I have the AUX latched to the MONITOR/PHONES section, I hear no noise unless the green MASTER AUX knob is turned up.
No rise in noise floor when MONO is latched, and latching the L/R on channels themselves makes no difference

If I the EFFECT is latched to the MONITOR/PHONES section, I hear no noise unless the BLUE EFF knob is turned up. No rise in the noise floor when MONO is latched. No changes to the noise if latch the L/R on the channels.

Overall the offending noise always sounds the same when monitoring it in either STEREO, AUX and EFFECT mode.

thanks


EDIT
Thought I might add, I'm not sure the MON latch really had any noticeable affect on the offending crackling noise tonight, it was very present the whole time during test and only varied occasionally and when it did it wasn't when I was latching the MON (PGM/CUE) button.
 
Thanks for all the detail.

This is a potentially complicated issue.

I haven't had the time to take all your notes and study them within the context of the block diagram and schematics. But I know I've experienced weird global noise issues like you described as a result of weak internal power connections.

I would start by tipping the unit up, removing the bottom cover, locate the MONITOR PCB (that's the one with all the record enable switches on it), visually inspect for damage and any loose connections, and then re-seat each connection. With the unit still tipped up and the bottom cover removed, power the unit and see if the problem persists. If it does, then while monitoring the noise manipulate each of the connections to the MONITOR PCB and see if you can effect any change in the noise (i.e. if you can make it louder or softer, or make it more "skritchy"...*any* change, I want to know what connector causes the change.)

Report back.
 
I've taken the back off and the PBC has no signs of damage or anything at all out of the ordinary after looking over it.

After putting the connections back on and reseating the PCB I turned the 388 on while it was still on its side and the noise seemed to have stopped.

I started jiggling the connections on the back and have noticed the white 116 connection makes noise when play around with it. A noise very similar to the one I was initially concerned about but sounds different (perhaps only because i'm playing about with the connection this time).

I kept playing around with the 116 connection until the noise stopped for a good amount of time, then I turned it off and I lay the unit down properly. I turned it back on there was bad noise coming again so I put it back on its side and messed around with the 116 connection until and stopped again and slowly put it back down again. No noise. Turned it off and on. No noise. I left it on for 10 mins and still no noise. Turned it off an on again for another ten and still no noise.

I bet if I out it on its side again and played around with the 116 connection again it'd come back. Ill leave it for tonight, start it tomorrow and see if the noise comes back, if it doesn't ill see if I can make it come back by playing around with the 116 connection again.

I also found this thread when searching for monitor PCB problems and this person seems to have had the same problem and solved it by recapping the monitor PCB.
https://homerecording.com/bbs/gener...ng-tape-and-gear/tascam-388-anomalies-296452/
 
J116/P116 is the L/R audio output of the monitor amp.

I would start by reflowing the connector solder joints.
 
well it would seem that doing this has fixed the issue. The issue was always intermittent so hopefully it doesn't come back. Ill leave it overnight and see if I can make the noise come back tomorrow . . . but other than that I think we might have solved this one!

really appreciate your help sweetbeats!
 
You must log in or register to reply here.
Back
Top