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Vintage Tape (Audio), Cassette, Wire and Magnetic Disc Recorders and Players Open-reel tape recorders, cassette recorders, 8-track players etc.

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Old 29th Apr 2020, 11:04 am   #1
dan_DNA
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Default Tascam 388 lockup project

Hi all, hope everyone is observing social distancing regulation and remaining locked in their studios away from their family, friend and sunlight - at least everyone else knows how we feel ALL THE TIME now eh?

Anyway, I'm attempting to revisit an old issue with my Tascam 388, and wondered if anyone else has had a similar fault, or may know something that I'm missing.
I inherited the machine in very good condition, everything works fine except track 4 wont record, or rather it does record but it just records silence. I've made a little video of it here https://youtu.be/_hqf8H-V6vY

I've tried swapping the input cards over but the problem remains on track 4 so I'm leaning towards the idea that it is the TEAC monitor PCB card?
There is a monitor PCB card for sale now on ebay but I don't want to buy it if it's something me and the old man can fix it in the shed.

If anyone has any ideas or suggestions I would love to hear them.


thanks!!
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Old 29th Apr 2020, 2:52 pm   #2
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Default Re: Tascam 388 lockup project

I serviced a couple of these recently. A common problem with some channels in one was intermittent input source switches (top of channel strips). The 3 position switches just needed to be well cleaned.

Another problem on one channel strip was a dead 8 pin amp IC, a TL 032 from memory.

Another was a poor or fatigued connection on the joiner PCB which straddles the bottom edges of the eight channel strip cards. I had to resolder a couple of pins to the PCB.

Just on these machines, if you're looking for that funky analog tape sound when you push the levels hard in record, you may only get it with the DBX NR switched off. Switched in, the DBX will probably run into serious clipping before the tape saturates and you will only get a hard, nasty distortion which is not from the tape but the electronics. DBX assumed users wanted to avoid tape (or any other) distortion. It was perhaps a different world back then!
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Old 29th Apr 2020, 4:34 pm   #3
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Default Re: Tascam 388 lockup project

Very interesting piece of kit ! Have you looked at the Service manual which is very extensive.
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Old 29th Apr 2020, 4:52 pm   #4
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Default Re: Tascam 388 lockup project

thanks for the suggestions, ill go over each of those things anyway, cant hurt to give some other likely problems a bit of care and attention.
Great point regarding the DBX.
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Old 29th Apr 2020, 4:55 pm   #5
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Default Re: Tascam 388 lockup project

Yes i was lucky enough to get it with a full original manual that has pretty much everything in there, including some excellent tips on recording, something many modern companies dont do anymore. Tascam didnt want people to be disappointed in their purchase!
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Old 29th Apr 2020, 6:49 pm   #6
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Default Re: Tascam 388 lockup project

Had a quick look at the very large Service manual and relevant schematics, all very complex looking, there is lots of digital control.

I think it is very difficult to make any real judgement if the Monitor PCB is the likely culprit, it could be.

Does a previous recording play back on channel 4 and does the channel 4 meter then work , if not wonder about the meter amp PCB.
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Old 29th Apr 2020, 7:20 pm   #7
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Default Re: Tascam 388 lockup project

yes ive tried a tape that has stuff recorded on track 4 and this plays back ok, you can even assign channel 4 to any of the other 7 tracks, its just when you try to record anything onto track 4 there is no joy, and there is no VU meter action going to tape.
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Old 30th Apr 2020, 4:16 pm   #8
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Default Re: Tascam 388 lockup project

okay, so had the Tascam on the bench today.
Tried swapping over the Channel PCB for channel 4 with channel 3, no change. can strike off the problem being channel related.
Swapped the faders between 3 and 4, no change, can also rule this out.

Next we removed the Monitor PCB, checked it over visually and put a multimeter over it to test all the points we could, everything seems fine with the card. checked the continuity of the cables for tracks 1-8 going to the motherboard (1) PCB and the Buss A PCB, all fine again.

Ive included some pics of the head, although i dont see why it would only be one track not recording, but just included them here in case anyone can see anything in them.
https://www.dropbox.com/s/bemdfqtkxx...204_4.jpg?dl=0
https://www.dropbox.com/s/6v2u5hays4...215_3.jpg?dl=0

one last thing - after we had put it all back together as i unplugged my guitar (which i had been using as a sound source to check the problem) I noticed the needle on the VU meter went up to just below -20.
Every time i held the tip of the jack onto the metalwork of the guitar the meter seemed to register a very low signal (i was using a balanced XLR to 1/4" jack to plug my guitar into the XLR input of the 388).

Does this prick up anyone's ears?
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Old 1st May 2020, 12:11 am   #9
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Default Re: Tascam 388 lockup project

The heads look ok to me and the fact that one head does record and play and channel 4 comes out ok, indicates that the head and the monitor sections are ok.

You need to find out if the record signal is reaching the head. I haven't had time to study the manual, but I suggest the fault ies in the record/bias section.
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Old 1st May 2020, 12:23 am   #10
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Default Re: Tascam 388 lockup project

One thing you can try is to record over a previously recorded tape. Does track 4 erase the previous recording, if it does not then that channels bias amp is faulty, if it does you need to make sure that bias is reaching the head in record.
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Old 1st May 2020, 12:52 pm   #11
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Default Re: Tascam 388 lockup project

hi
thanks for the suggestion.
when i record on track 4 of the tape it does erase previous material, so i assume the erase head is working?
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Old 1st May 2020, 12:59 pm   #12
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Default Re: Tascam 388 lockup project

Yes, it also means the bias amp is working. I think the problem is with the record amplifier for CH4
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Old 1st May 2020, 1:32 pm   #13
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Default Re: Tascam 388 lockup project

Usually the meter takes the signal before the record amp. Since the meter is also not registering on that channel, it suggest the problem is upstream of (before) both.
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Old 1st May 2020, 2:46 pm   #14
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Default Re: Tascam 388 lockup project

Quote:
Originally Posted by Michael Maurice View Post
Yes, it also means the bias amp is working. I think the problem is with the record amplifier for CH4
thanks, ill look into this next.
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Old 1st May 2020, 2:48 pm   #15
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Default Re: Tascam 388 lockup project

Quote:
Originally Posted by TIMTAPE View Post
Usually the meter takes the signal before the record amp. Since the meter is also not registering on that channel, it suggest the problem is upstream of (before) both.
so i should be looking between the tape input and the meter?
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Old 1st May 2020, 10:39 pm   #16
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Default Re: Tascam 388 lockup project

it would appear so.
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Old 29th May 2020, 11:59 am   #17
dan_DNA
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Default Re: Tascam 388 lockup project

okay, so latest on the 388 repair job. We've tried swapping over the input cards, no change, so its not the input. Managed to get to the meter amp PCB and swapped around the plugs for the meters for channels 3+4 (4 being the meter than isnt registering) with the plugs for the meters for channels 5+6, and hey presto 4 worked, but the problem was now on channel 6, as would be expected.
So the problem isnt the meter amp PCB (also checked continuity on those two cables, channels 3+4 and 5+6, theyre fine).

IMO this has narrowed it down somewhat to either Buss A, or Buss B. The input cards all go to Buss B first and are then distributed to Buss A. Buss B has the track select buttons on it, which all seem to be working, flashing red etc (and any channel can be assigned to track 4). Buss A is where the assigned inputs are then distributed to the track and therefore the meter amp PCB.

Any ideas what we might be looking for on Buss A PCB?

Other option is Ive found one on ebay for 48 bucks, but as im in the UK the seller wont ship it.
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