Tascam 48 record button and dim LEDs and calibration


New Member
Nov 20, 2012
Gear owned
Tascam 48 - Tascam M-312b
Hello there, this is my first post on this site. I’ve been using it for info over the last few months and have found it to be a great resource.

I’m currently stumped right now as to what I did to my Tascam 48 8-track. I bought it in relatively good condition and have had the rollers rerubbered by Terry at Terry's Rubber Pinch Rollers & Wheels He did such a great job and I have been setting it up and calibrating it over the last couple of weeks on my off time. The functionality was working wonderfully until…

Upon getting my RC-71 remote, I noticed that the rewind button didn’t work on it. I took it apart to examine it and found that it all parts checked out fine and the issue was in the connector pcb on the back of the machine. The connector pcb didn’t allow the signal to be passed through to the little capacitor on it, so I bridged it with a small wire and some solder. It now rewinds fine.

While doing this I accidentally touched some of the other open leads to the chassis and it made a very small spark. I have found that the green led for the spooling feature above the FF and RWD buttons is about half-lit; same for the Record LED when in Record mode. The green Stop LED and Yellow Edit LED don't work at all.

All other functions on the deck work fine. I’ve checked the fuses and nothing wrong there… So now it looks like I’ve gotten myself into a little bit of a mess.
Any suggestions on where to look? I’ve seen in other threads people talking about blown ICs or relays… Is an IC the same as a relay in this scenario?

I'm new at this and want to learn as much as possible about circuits, but also have a general understand on how to remove components, solder and desolder caps, etc.

Any suggestions are welcome!!
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I have had a OB48 1/2" it is a very good machine.. now I have the MS16 1"

1. Have you check al the fuses ? "very important"
2. Do you have the manual ? if you dont I have it right here : )

Best regards
Troels Nyborg

Voxphonia Records

Sounds like you damaged a function on the system control board. You may have toasted a transistor or two.

This will require some work to go through the board to find what is wrong.

You need the service manual with the schematics along with a tester that can check diodes and transistors.

It appears to be localized to the functions mentioned.

You might 1st want to check the "rail" transistors. Those are the larger ones secured to an aluminum heat sink.

Not a fun job.
I have a .pdf of the wiring schematic you are welcomed to, and I may be able to help you track that problem.

I have a 38 open now, and there is only one (1) rail transistor that is for the power side of the control board.

So most likely your problem is with a board-mounted transistor for the remote circuit.

P503 on the control board connects to the remote control external jack. It can be identified as it has a red 10-pin plug that connects to the control board.

It is important to know what your serial number is, because, according to Tascam, PCB assy from 38s with S/N 400001 and above have a different layout than earlier units.

I have attached the 38 series logic schematic


  • 38 Logic Schematic Layout.pdf
    426.6 KB · Views: 25
Thank you guys very much for your replies! When I get time in the next few week ill try to take another look to figure it out. I'll let you know what I find!
no need to post the schematic... I have the manual with all that in it. I just didn't know where to look. I appreciate your help... If you could direct me to a specific part or parts, that would be great!! Thanks so much!!
I'm working on getting my Tascam 48 8-Track up and running, but haven't gotten to the issues above. I just want to use it since it is still fully functional. So, I'm wondering about calibration...

I have come to the biasing part of my calibration...

I'm wondering if I have found a typo in the manual or if I should just trust what it says and go with it.

From my experience, when biasing a machine, you drop your level by going counterclockwise and once you hit your low point, go back clockwise until you peak. Then, continue clockwise to overbias and drop the needle again to a specified amount....

The Tascam 48 Manual says, "Begin recording a 10k signal and turn your trimmer COUNTERCLOCKWISE for a minimum level reading.(This seems right). From that position turn the trimmer CLOCKWISE until peak level indication is obtained.(This seems right). Then turn in back COUNTERCLOCKWISE until the reading on the level meter drops back 3-5dB from the peak reading as shown in Fig. 7-26.

So, that last step seems backwards from what I'm used to... Anybody want to chime in with your experiences on this machine?

Thanks for any help ya'll!
So, I've gone against what the manual says and kept turning clockwise to go "over the hump" and back down about 3 db... So I guess that is overbiasing. Whether this is correct or not, I'm not sure. Overall, I think it sounds good, but I might be missing something still or haven't run into any issues since I've only recorder a few things.

Any ideas?
Hello, I am looking for a Tascam 48-ob reel to reel schematics, I am willing to pay for a pdf version, any help will be appreciated. Thanks!
Hi @Gcalo,

I have just bought a tascam 48 and need the service manual or at least the schematics...Found your post and wondered if you could post it on here or email it to me?

Hey Guys, I don't have access to a scanner, but I can take photos of individual manual pages if you want. I do think there should be a free resource for such old gear. In fact, if I have time, I'll take photos of the whole manual and then compile as a FREEEEEEEE pdf!
By the way, my issue with the dim LEDs still stands to be fixed. Upon comparing my manual to the that of the actual Control PCB, they are in fact different. I have a new version of hardware that is not reflected in the manual... making it hard to fix the issue. Any pointers?? Also, does anyone have a Tascam 42 or 48 manual that they can check to see if the Control PCB Schematic and Blueprint are different than my attached ones? Reason I ask is because apparently the 48 shared the same PCB as the 42 and maybe they updated the manual at some point with the new circuits... Tascam 48 Control PCB Schematic.JPGIMG_0596.JPGIMG_0595.JPG Tascam 48 Control PCB Left.JPG Tascam 48 Control PCB Right.JPGDim Record LED.jpg Dim Spool LED.jpg
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An update for my 48:
-Spooling LED is still half-lit when in Spool mode
-Red LED currently half-lit in Record Mode
-Edit LED never even comes on anymore
-Stop LED never works either.

All other function on the machine work perfectly!
I'd like to give an update to those out there that this may help... Which may be none! Anyway, I actually opened up the front panel to where I could access the dim LEDs and was able to see that they looked burnt. So I replaced and guess what... All is well with bright LEDs! Duh!!! I didn't know that a failed LED could just go dim and not go completely out. Lesson learned.

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