Tascam 388 Fader/VU/Actual Output differences

[frcake]

Hello everyone!

I am an owner of a Tascam 388 which has been somewhat serviced a long time ago but there are still some problems.

Now the problem I'm going to describe happens on *all* channels in regards to Left/Right balance.

Setup:
I'm sending a static noise from my soundcard to 1-2 input, connect the tascam 388 output back to the computer to the spectrum analyzer which is in dual-mono setup L/R.

Example 1: Bad fader alignment, VU Meter shows equal gain, Difference in actual output levels:

Example 2: Bad fader alignment, Bad VU L/R reading, Equal actual output levels:

Any ideas about this? I've opened the top panel but I don't seem to find anything regarding the line trim, I'm not even sure if it's the line trim to be honest, maybe a combination of line trim & VU calibration? Or something totally different?

Again, this happens on all channels, so all channels must have this weird fader positioning to have an equally stron L/R output.

I have the 388 manual, so if I have to open the machine, you guys could help me do it correctly or point me to the manual..

Thank you!

 

[Psychotron1976]

Clearly, your VU-Meters are not calibrated correctly, so the differences you have. See the section 1-12 (page 61) of the service manual, it's not complicated to calibrate.

 

[frcake]

Clearly, your VU-Meters are not calibrated correctly, so the differences you have. See the section 1-12 (page 61) of the service manual, it's not complicated to calibrate.

Hmm I think it's more of a master channel problem.
If I have a mono signal (just turn the panpot in the middle) the imbalance is the same. The only way to balance a mono signal is to turn the panpot exactly (in my case) at 3 o clock. This is the only way to have a true mono output from one single channel.

These are my panpots if I want any channel to send an equal L/R signal back to the card, so it seems like all the channels need exactly the same amount of panning..

 

[Psychotron1976]

To confirm, see the signal for each channel at the PGM outputs to see if the imbalance is present or not.

 

[frcake]

To confirm, see the signal for each channel at the PGM outputs to see if the imbalance is present or not.

Let's say I have a 400 Hz signal going into all my channels from the card.

And I want e.g. Tascam mixer channel 2 to to go back to the computer. If the panpot is in the middle VU of channels 1&2 both show -3 db or, the same reading anyways..
The computer input reads a differenge of around 6 db. So I have to turn the panpot right so the new readings of each PGM VU reads L -8~ R -1~ .. so roughly those 6~ dbs of difference I saw before in the daw/card input.

PGM Masters are all the way up to be sure they are the same.

But I think the machine has a serious problem. I switched the BAL/UNBAL output in the back and the UNBAL out kills one output channel completely.. might be related might not I don't know..

I thought maybe there was a way to calibrate the master out or something but.. maybe I'm cooked :/

 

[frcake]

Adding to the tests:

I checked the signal from SEND. All channels show about the same signal strength (nowhere near the consistent difference needed to balance out the master)

Sent all channels to EFFECT/AUX post fader, Channel 3 doesn't get through to the sends, sadly.. but I can get a pretty ok L/R with master AUX & EFFECT at roughly the same level...

Sends are all cranked up to ensure same signal strength..

 

[Psychotron1976]

Reading again your first message, I still think you have mis-calibrated VU meters. See the Block Diagram (pages 47/48 of the service manual), the L/R VU Meters are after the Stereo Faders and just before the physical output. If they show the same volume but you have different results at the output, your VU Meters are clearly mis-calibrated.
I'm not sure to understand your other manipulations (compensate with pan potentiometer) and especially when you said "All channels show about the same signal strength", are you using the 388's VU-Meters to evaluate the signal level? Because if yes and if they are not calibrated, you can't be sure. After that, maybe there is an issue elsewhere but first thing is to calibrate your VU-Meters to evaluate properly your signal level.

 

[frcake]

Reading again your first message, I still think you have mis-calibrated VU meters. See the Block Diagram (pages 47/48 of the service manual), the L/R VU Meters are after the Stereo Faders and just before the physical output. If they show the same volume but you have different results at the output, your VU Meters are clearly mis-calibrated.
I'm not sure to understand your other manipulations (compensate with pan potentiometer) and especially when you said "All channels show about the same signal strength", are you using the 388's VU-Meters to evaluate the signal level? Because if yes and if they are not calibrated, you can't be sure. After that, maybe there is an issue elsewhere but first thing is to calibrate your VU-Meters to evaluate properly your signal level.

What I mean by compensate with panpot is the following. Imagine I send a signal only to channel 1 and nothing else. A mono signal. If I add the channel to the mix and leave the panpot untouched, there is a difference betweren L/R output signal strength. If I turn the pot towards the right channel (so more of R is mixed to the final Master signal) then I can balance it.

So forget about anything else, just think about 1 single channel, 1 input to master. Shouldn't that produce an equal L/R signal with the panpot in the middle?

I hope I'm explaining it well enough, thank you so much for trying to help!