Tascam 388 REC/PLAY PCB ISSUE - Fixed

Nothing new so far, i have not received the replacement card yet.
I got a little starting point on another board.

"Its sounds like you have a fault on that card, So its a case of inputing a signal, say 1khz and following it through from start to finish.

Record a 1khz signal onto the tape ( you can find tone generators online), say track four then put the faulty board in channel four, playback the signal then trace it using the schematic as you go.

Your 388 uses op amps a lot so get the data sheet of your op amp/s, find which pin is out, usually pins 1 and 7 on dual op amp ic's with pins 4 and 8 being power supply. Same goes for transistors., check for a signal at the emmiter on NPN types.

A scope here is invaluble, but you can do it with a DMM as long as your DMM's AC range has the spec. If not, check your voltages on op amps and transistors.

I'm afraid it's a long fiddly job sometimes, and hard to tell you exactly what to do, but Teac manuals usually are excellent and walk you through. I havn't had time to go through your manual, but that's where you should start along with the above steps"

Feel free to add help. If im not responding anymore i sat myself on fire during "repairing";)

Thanks
 
Hello friends,

i have some news.
I made another test with swapping cards as follows.

With faulty R/P AMP PCB in SLOT 6/8 i recorded a testtone
on TRACKS 6 and 8.
While playing back the usual failure, TR6 plays well and
absolutely nothing on TR8.

Now i swapped the faulty card from SLOT 6/8 with the working
one from SLOT 5/7.

I played back the tape and which wonder, the testtones on TR6
AND! TR8 play back well!

I did this procedure for testing the erase function, and it works too!

So to me this means that the fault on the R/P AMP PCB is somewehere in
the "reproduce-path" or "playback-path".

I will provide you with a high quality scan of the PCB schematics in the
upcoming days, i am sure someone can help me with failure hunting.

Thank you very much for your tips.
Al
 
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A shot in the dark.

On the schematic on sector B4 i see switch symbols (rec) (play) and an arrow which indicates (play) on the graphic.

What component on this board switches from record to playback mode and vice versa, the Silicon Transistors?
 
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688 said:
A shot in the dark.
On the schematic on sector B4 i see switch symbols (rec) (play) and an arrow which indicates (play) on the graphic.

What component on this board switches from record to playback mode and vice versa, the Silicon Transistors?
Click to expand...

Relay K102, if I'm not mistaken. Those do have a tendency to get stuck in later years.
 
this could be not that far off because as i said earlier in the thread, the particular card
has had some oxide buildup and was very difficult to pull out.
these relays k102 and k202 sit right above the connector pins, so maybe k202 sucks ehh stucks.

edit: Unfortunately the original Part NEC MR62-24S is discontinued,
so I have to go with a chinese one.

replacement relay part ID : OMRON G5V2-24, price 1,40€

thanks for the hint.
 
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I made another test.
The results maybe rule out the signal relay, i have to say maybe
because i am not 100% sure how these relay fellas work.

Test procedure.

1 faulty REC/PLAY PCB sits in its original SLOT CH 6/8
2 loaded a blank tape in the machine.
3 pressed play + record to enable record ready mode,
tape is rolling, red rec led on transport is blinking
4 now i push the record enable button for TRK1 and while
listening with my ear near the opened card bay
- i hear a very clear "clicking" from the relay K102 (resp. K202)
5 the same procedure for following TRKs 2-8
- all relais make an audible clicking noise while record enabling/disabling
6 i did the same procedure and watched the meters, meters 1-7 dont move
while pressing the rec enabling buttons for 1-7
- the only one that "moves" while pressing the button rec enable 8 is meter 8.
its movement is very very slightly, even way under the -20db marking, but all others
werent moving even slightly...maybe this information can help while looking at schematics.
- no audible clicks or pops over the headphones during this " movement" needle is very very slightly moving
but still, only on 8.
Conclusion: none,yet.

So now here the question.
If i enable the record mode and hear the "click" from the relay, are the contacts inside closing
or opening?
remembering, RECORDING and ERASING is working fine with the card.

If it is "closing" while playing back, then it could maybe be totally oxidized or otherwise aged contacts,
if it is "opening" while playback, then i would think the relay is either working properly or its coil is damaged,
but then it would probably not "click".

Should i rule out this relay?
 
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i read up on relays.

NC-NormallyClosed relays - relay is closed in de-energized state, opened when powered
NO-NormallyOpen relays - relay is opened in de-energized state, closed when powered

The NEC MR62-24S (NON-LATCHING)was a convenient relay, so i guess its the NO-Type, i can't
find or understand this info in the datasheet. (probably NC-TYPE new info)

EDIT: alright i found new information.

Non-Latching

A non-latching relay has an initial position of normally closed (NC) maintained by the force of a spring or permanent magnet while no current flows. The normally open (NO) contact is maintained by the force of a magnetic field while current flows through the coil. When the current stops, the relay reverts back to its initial NC position.

Non-latching electromechanical relays are useful in control applications when the switch must return to a known state if power is lost

This would mean that it could be indeed contact problems, because during record mode engaging the relays would open, in play mode close contacts
again through the force af a spring and there could be the contact problem.

Can someone confirm this or shed some light.
Thanks
 
Relay K202 ruled out 99%.

I measured the pins on K202 and compared my measurements to K102.
Closed position (powerless) as it should be and same measuring results as the
working side.
Search goes on.
 
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A quad NOR gate, hmm? Looks like only 3 of the gates are used, and two of those are acting as inverters (both inputs tied together). If the inputs remain steady it should be fairly easy to verify if it's behaving itself.

Interesting that the low-pass filter in the top diagram is also referred to as 'U105' - that has got to be a typo - the parts list describes U104 as an LPF, and I very much doubt you can get a NOR gate to do that (Notwithstanding that the EDP Wasp abused digital inverters in its filter circuits, producing very weird distortion effects)
 
I am very happy!

I received the replacement REC/PLAY PCB ordered from UK in the mail today.
The Tascam was still sitting on my workbench waiting for it's fix.

I popped the card in and recorded 10 minutes of testtones ranging from 80hz to 4khz
on a Maxell UD Tape.
The PCB is working flawlessly and it doesn't need any calibration, record and reproduce
levels of channels 6/8 show no significant differences to the other 6 channels.
No unwanted noise, disturbances or flutter occured, so i am not going through
any calibrations.
All good!

Still, I will try to fix the faulty board, it is way easier now that i dont have to
worry so much about destroying it.

A nice person in UK is willing to send me some relays (K101/K201) and
the NOR-Gate is still available from electronic suppliers.
I'll see.

Now the 688 have to make room for it's fat ugly mama to take over:listeningmusic: .
Need to build a bigger studio table now.

So far thanks for the help and i will report back if I am making progress
fixing the now spare card. Its actually quite fun to learn a little electronics.

Thanks
Al
 
hello

i've the same problem with track 7

in stop mode : mic/line/png --->the meter run ok on every track when assign 1/2 3/4 etc etc

in rec mode: the same

in playback mode: no signal or the signal is very very low

yesterday the tascam was perfect and today when i touch the trim for rec volume, play volume etc etc i notice this problem

i have swap the pcb card (7 on 6...7 on 5 etcetera and the problem it's the same

i have swap the card 5/7 with 6/8 and the problem it's the same

have disconnect every cable and i have used isopropanol on every card and connector another time
i have used a demagnetizer for the head and disconnect and connect.

now the tascam is perfect but i can't rec on the 7 channel...

any idea?
 
You have swapped the REC/PLAY cards already and the fault remains on TRK/CH 7 no
matter which card you have seated in socket 5/7?

And sometimes you get levels from TRK7 while playing back the tape and sometimes not?

You'll have to find out if the fault appears during recording or playback.

Record a test-tone on Tape-TRacK 2, then physically flip over the tapereel.
Put the Input selector on mixerchannel 7 in the RMX position, push
the red LR Assign button on CH7. Pull up the STEREO LR FADER and
the FADER CH7. Do you hear the recorded signal(backwards)?

The same you can do the other way around,you record a test-tone
on TRK 7. flip over the tapereel and listen to TRK 2 to check if it
has recorded the signal on TRK/CH 7.

What do you mean when you say "touch the trim for rec vol, play vol" you mean
the variable resistors on top of the REC/PLAY PCB cards?
 
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688 said:
You have swapped the REC/PLAY cards already and the fault remains on TRK/CH 7 no
matter which card you have seated in socket 5/7?

And sometimes you get levels from TRK7 while playing back the tape and sometimes not?

You'll have to find out if the fault appears during recording or playback.

Record a test-tone on Tape-TRacK 2, then physically flip over the tapereel.
Put the Input selector on mixerchannel 7 in the RMX position, push
the red LR Assign button on CH7. Pull up the STEREO LR FADER and
the FADER CH7. Do you hear the recorded signal(backwards)?

--------------------i use a test tone tape but the vu meter on track 7 don't move

if i connect mic,line in, pgm in the vu meter it's ok



What do you mean when you say "touch the trim for rec vol, play vol" you mean
the variable resistors on top of the REC/PLAY PCB cards?
Click to expand...

------------yes
 
thank you for the help but....
i'm new in the analog world...

after re-swap the pcb and no problem solved... i try to rewind all the tape... change from right to the left the tape... and problem solved...


i think after many attempts the tape is corrupt...

sorry for my english... and thank you!!!
 
Hello,

I'm having the same problem

Where did you find/buy the REC/PLAY PCB? I Can't find one anywhere :(

Thanks!!
 
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