Noisy Preamps

[surjer]

So my 2488 has started to experience a new problem which is a "noise" that I can only chalk up to the preamps. Thing thats weird is that it does it on every channel on every input. If I arm a track for recording it gets this nasty noise. Its not super loud but its there. I am recording in 24 bit mode and using the same power source as before but i've experienced this noise no matter what location i take it to. Doesnt have to have a mic plugged in to get noisy either. I have cleaned it pretty thoroughly with contact cleaner and that has not fixed the issue. I did have a problem with the little rubber grommets coming out of the XLR connections on the back but I just popped em back in. They got stuck in the XLR cables somehow. Its a pretty tight fit... Any idea's? I have formatted the hard drive and cleaned everything out short of taking it apart. If there is a known trouble spot i am not against taking it apart i just dont want to take it apart with no idea of what might be wrong. (Maybe I should just do it tho?)

 

[berl]

2488 Power supply problem IMHO.
Try inspecting it for doomed condensators, or change them for new ones with good quality ones (105°, long life...)

 

[surjer]

Hello berl! Thanks for your quick response! Any particular capacitors in mind I should check out? Am i just looking for "burnt" looking caps or is there an official way to check for bad ones? Looked to be a lot of capacitors in there so not sure exactly how to go about methodically checking them. Thanks in advance,

Jerry

 

[berl]

Jerry, could you take a pic of your psu inside?
Before that, the best thing to do would be to check the supply voltages with a scope... but just check the voltages with a meter would be fine.

 

[surjer]

I took an overall picture last night when i had it opened up. I am guessing you want a little more detailed focused on the power section than in this picture correct?

Let me know where I should check voltages. i do not have a scope but i do have a multi meter..

https://www.dropbox.com/s/vvl08qz9dsv8w ... .08.21.jpg

 

[surjer]

Also here is a small track of the noise that i am getting. The TRACK001.wav is the direct dump from the tascam and the mp3 i just cranked up the levels to make it easy to hear without turning up your speakers.

https://www.dropbox.com/sh/cl0n40kilil7v5m/br-kh8n_po

 

[berl]

Waow Jerry nice clues... it sounds like a condensator is on its last legs (in french we'd say "il perd ses bas" : loosing his pants ;-)
No problems with the hard disk ?
If you have this sound on ALL the channels yes the PSU (on the bottom right on your pic) must be checked. That's not the only possibility

If anyone has the schematics it'd be very appreciated !!!

BE CAREFUL : high tension here !
You will check the tensions on the side of the PCB that is on the left (hard disk side) of the white line, with your multimeter on the 20V range (highest voltage there will be 12V and around +/- 15V
You can test the voltages on the output connectors by gliding the meter probe along the wire till you reach the metal part of the contact that holds the wire. Black is usually 0V, you will have usual voltages that goes to the hard disk (+5, +12) and more interresting for us, the connector that goes to the audio PCB.

Voilà, now the ball is on your side !
Please also take another pic of the PSU alone.
Bernard

 

[surjer]

OK, I will dig back into it in a couple of hours and try to get some tests ran. You asked about the hard drive and I did have some stuff happen that I thought might have been hard drive related in which the errors only occured after those incidents. I was recording a live set and when the main band came on the tascam would lock up and eventually error out. I would have to cold boot it and start a fresh song and it kept happening. Then about a month ago i was recording drums in my garage and it started doing that same thing. I posted on this forum and it was suggested to put some soft cushion or foam underneath it to absorb the shock and once I did that, i did not receive the errors or lockups anymore. I am not sure if the two problems are related but i figured the more information I give you the better off we are at coming to a resolution. Thank you kindly for all your help. I hope I can get this thing working again because the preamps on my M-audio interface are crap compared to this Tascam and being limited to 2 inputs is killing me. Nevermind having to take my computer and break all that down evertime. Cant WAIT to get this tascam back on line..

 

[surjer]

OK Here are some shots of that area a little more zoomed in and closer. Better detail for you hopefully. Nothing stands out to me.

Voltage test resuts:
Going to HD and CDROM measures 5.05v and 12.05v
Going to the board is 5.07v on all the red ones and 3.3v on the two orange ones. I held each one in place for several seconds and noticed 0 fluctuations at 2 decimal places. The two big caps are labeled 105d C 250v but i did NOT tests on them.

https://www.dropbox.com/sh/3f5pj3q0zhhvvsl/9iCWMPh1ID

https://www.dropbox.com/sh/3f5pj3q0zhhvvsl/9iCWMPh1ID

 

[berl]

Voltage test resuts:
Going to HD and CDROM measures 5.05v and 12.05v
Going to the board is 5.07v on all the red ones and 3.3v on the two orange ones.

Well, nothing wrong here The white wire tension?

 

[surjer]

just got the white wire and that one measured 4.17v. Not sure what it should be but i would guess ~5.0v?? Now we really need a schematic ehh?

 

[berl]

Where goes this white wire ?
Do you have located the preamp section ?

 

[RealTime]

Where goes this white wire ?
Do you have located the preamp section ?

Hi, the white wire is the 'power good' signal. The measured value of around 4V indicates the PSM outputs are all in range.

With regard to the noise, do you have the phantom power switched on? If yes, switch it off and see if that helps. The fact that you can record the noise indicates a problem with the input channel board (I have a very noisy headphone output, but it doesn't affect the recorded signal). The power supplies for the analog section are provided by connector P2 on the power supply module (just next to the main P1 connector). These supplies are generated separately from the digital (CPU, hard drive, etc) supplies. Check that you have

P2-1: +12V
P2-2: Ground signal
P2-3: -12V
P2-4: +5V

Do you get the same problem if all gain controls are turned down to their lowest setting? Also try setting the effect returns to zero to eliminate those inputs.

Ian

 

[surjer]

Thanks Ian, I am away from my Tascam for the next week so wont be able to test anything for a bit but I have tested this with phantom voltage on and off. When selecting phantom power it will stop for a second and then starts back up again. This noise occurs with all levels on the input trims being turned down all the way. When turning up the trims for input you will hear the usual "shhhhhh" of the preamps getting louder as you would expect but the weird noise does not change. With all input trims set to the far left or what is labeled as "line" and the volume turned up on all the faders you can hear the noise once you assign a channel to an input. The more inputs you assign the louder the noise gets. Input B is by far the noisiest. All effects sends are at 0 as well. Thanks so much for your help. I will check those voltages when i return but i am pretty sure I have already and those looked good. I did completely remove ALL connectors and clean every board in this thing and made no difference at all. (I had a living room full of tascam parts! lol (Thankfully no left overs upon reassembly) =)