388 very quiet during stereo playback

QUOTE=rob388;4424174]No offence taken.

I've got a bit carried away ��

I'll put her back together today.

Just to clarify, the signal generator I used years ago was box like machine that could generate square waves, saw tooth waves, sine waves and some others, we passed these signals through electronic circuits and measured how these waves were affected with a cathode ray oscilloscope.

I carefully read the 'another 388 problem' thread last night and from what I made out the tone generator was an app from a phone that could generate tones of different frequencies, is this correct?

I hope this is correct as I don't have a signal generator or oscilloscope, these were used on an electronics course I took many years ago. I've forgotten about 95 percent of what I learned so it would be fair to say that you guys are dealing with a complete novice, albeit a willing one!

I'll get everything back together today and report back.

How can I upload photos?

RFR I know what you mean!

Many thanks guys.[/QUOTE]

For the 1 kHz wave, I went to this site:
Custom Sine Tones | Audio Test File Generator

You can generate whatever you want and then download it to your computer. I think the longest it will let you generate is 10 seconds. So I did that, opened it up in Reaper (but you could use any DAW or wav editor), and set it on repeat.
 
Thanks famous beagle, i've just downloaded an app that plays tones from 10hz right up to 30khz, i think this should be ok to use for testing.
 
Ok it's all back together.

I've connected via the line inputs an audio source from my phone and here's what i'm getting.

Powered speakers connected to the monitor outs and my headphones connected to the headphone socket on the front of the desk.

The red trim knobs and fader are set to a nominal level.

With the white aux button latched(on) at the far right of the unit i'm getting good audio through both the headphone and monitors.
I've carried this test out using all channels/tracks ie connecting my audio source to each individual cahannel.
I'm able to control the volume with the green aux knobs, the channel aux knob and the master aux knob both effect the audio as you would expect.

I've carried out the exact same test with the EFF button(far right of the unit) latched(on) and got the same results.

With the stereo switch latched(on) far right of the unit, the stereo master fader up to the shaded area and the red L R button latched(on) i'm getting audio through both the headphones and the monitor speakers but it's barely audible. You have to turn the stereo master fader right up to the top and the monitor volume pot right up to hear this barely audible audio.
As I did with the previous two tests i carried the test out all through channels 1 - 8 and got barely audible audio all across the board.


I'm not sure if i may have caused another problem or it was an existing one, here goes!

Channel 3 - with channel threes aux(green button) pressed in, and the white aux switch latched on i'm getting barely audible audio. With the channels button unlatched it's fine.

In EFF mode channel three is barely audible.

And with a mic connected, trim knob set to a nominal level there is hardly any audio coming through the speakers or phones even though the ol led lights up if i shout a bit.

I'm pretty certain but not 100% it was ok before i went and got carried away cleaning things up even though i was extremely careful doing so.

That'll be the first and last time i get carried away on this repair project, any further advice i'll follow to the letter, appologies.

So thats where everything stands at the moment, i've put a new battery in the multimeter, bought a desoldering tool and soldering iron, some jump leads incase i need them and some switch cleaner/lube.

I've tried to be as clear as i can posting my test results, if theres any more info required i'll do my best.

Many thanks,

Rob.
 
Thanks for the advice, it's much appreciated :)

I've read through the thread a few times, i'll need to read a few more times to hammer this stuff home and keep referring to the Tascam 388 manual. Its going in slowly! I've had a thought, reading famous beagles thread it was stated that when he latched the L R switches he was getting no audio what so ever, which you accuratley diagnosed as the failed hex inverter mc14069. It wasn't switching how it should when it recieved information from the L R switches telling it to switch. Is that correct?

In my case i am getting some audio just not very much at all, would it be fair to say that my mc 14069 is switching ok but theres an amplifier stage afterwards that isn't functioning properly?

I could be way off the mark here, i'm just throwing stuff out there!

I'm still gonna follow the instructions in the thread, it feels like mine and famous beagles symptoms could be slightly different though.

Could a failed 14069 chip cause no output and very little output?

Thanks,

Rob.
 
IIRC beagle's symptoms included very faint signal which was, for all intents and purposes, considered to be "no signal". If an amp stage was the culprit, you would have no signal when monitoring the AUX or EFF busses. That's why I had him do that test.
 
Many thanks again, that makes sense now. I'm looking forward to fixing this, more reading first though, i feel its important that i try to understand what i'm testing for and why, I'll go through beagle's thread a lot more times whilst referring to the manual and hopefully start testing in a day or so.

Spotted the typo in the manual re the mc 14069

I have a vanagon manual just like that, it's only the torque settings that stop the engine flying apart!

It's 1.30am here I'll check back in soon.
 
It is *essential* you understand what you are doing and why before you do it.

It is essential you move slow and careful and methodically in your work. Double and triple check what you are doing.

May I suggest you practice soldering and desoldering on a scrap electronics assembly before taking the iron to your 388?

Proceed with caution.
 
Good idea regarding soldering practice, it would be good to get some practice I'm a little rusty for sure.

Still reading and studying at the moment.

I'll report back soon.
 
rob388 said:
Good idea regarding soldering practice, it would be good to get some practice I'm a little rusty for sure.
Still reading and studying at the moment.
I'll report back soon.
Click to expand...

Assuming that you DO need to replace a chip, it might be worth getting one of these:
https://www.amazon.co.uk/gp/product..._10?ie=UTF8&psc=1&refRID=17G5TJ0F7XZRJK8FVAYK

...I'm using a CSI8900 but it seems to be the same basic tool. I have not tried mine on a phenolic board yet, but it made recapping the Studer a breeze and should be infinitely easier next time I have to remove a chip.
 
Thanks for the info regarding the desoldering tool, i've spent this afternoon practising soldering, i took an old cheapo alba compact disc/cassette player apart(probably from the 90's) took the pcb's out and spent the afternoon desoldering and soldering components back in. I started off with diodes, caps and resistors and then tried my luck with two i think they were 16pin chips.

All went well and i was quite happy with the results, i'm using a standard soldering iron and a solder sucker tool, i found i had to really check closely after the solder sucker was used because just the smallest amount of solder left was sometimes enough to remove the green stuff(!) off the board when the components were wiggled out of their holes, so i went over the components at least twice to be certain and this seemed to work. I also when working on the chips skipped from side to side of the chip with as much distance as possible between soldering iron contact points so as not to localise the heat too much in one area.

I got good tidy joints and the solder flowed nicely if i fluxed the tip after every two solder joints, i was kinda hoping to find a hex inverter in there but alas!

Whats the reason for recapping stuff? And when you do this are you literally replacing every single capacator or are you targeting specific areas of a circuit?

I think i'm gonna get some more practice soldering and i think i should be ok with the standard solder sucker tool, thanks for sending the link, it's much appreciated.

Some more reading tonight, i'm gonna condense the other 388 thread down to it's bare essentials for what i need and hopefully later in the week i'll get down to some practical fault finding.

Thanks everyone.
 
Electrolytic capacitors dry out with age or can begin to leak.

General rule of thumb is to consider replacing the electrolytic caps on equipment 25-30 years old, or certainly if you see leakage. Your mileage may vary.

If it isn't broken don't fix it.

Good job with your practicing.

I use solder that has flux in it already. Makes it easier.
 
Thanks for the info Sweetbeats, much appreciated, it was nice to solder again after a good few years!

It's gonna be a busy weekend here for me, I'll post my progress as soon as I can, thanks again ?
 
She's working!

Listening in stereo as I type ?

I copied all the relevant info from beagles thread put it into a word doc, read, read and re-read whilst referring to the 388 manual. I then went through the fault finding procedure, I ended up with near identical results as famous beagle.

I then replaced the 14069 chip(it came today) and it plays loud and clear in stereo mode now ???????

Sweetbeats, the info you gave famous beagle and myself has been invaluable in carrying out this repair, I wouldn't have known where to start on my own with this.

Thank you so much for taking the time out to help, its massively appreciated ?

I owe you a beer ? ?

Thanks again,

Rob.
 
Yes!

That's tremendous. :D

So glad the resources helped and GOOD JOB studying and working through the troubleshooting process...it's paid off nicely. :guitar:
 
It has paid off for sure, and like I said earlier it wouldn't have been possible without your knowledge ?


I quite enjoyed the whole thing, it's rekindled my interest in electronics, no doubt the 388 will keep me on my toes!

Thanks again to yourself and everyone else that contributed ?
 
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