4-track cassette repair - sharp troubleshooters welcome! - diyAudio
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Old 2nd May 2014, 08:53 AM   #1
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Default 4-track cassette repair - sharp troubleshooters welcome!

Hi there,
I found this forum while googling for ideas of troubleshooting/repairing a tape recorder. I'm a musician and electronic newbie but always willing to learn more to manage my own repairs of my gear. So I'm turning to you. This post got ridiculously long, since I've tried to collect all info I can give.
If anybody of you experts would take the time to read, write and help me troubleshoot I'd be most grateful!

My old 4-track multitracker doesn't work. It did ten years ago. It's a Fostex XR-5 (similar to X-55), a mid-/entrylevel machine at the time. So it's not valuable enough to have a pricey tech fix it. Still, I'm up for the challenge of DIY.

Click the image to open in full size.

What's wrong?
When plugging it in/switching it on - the green LED for power and the red LED for record reacts (blinks once) but remain unlit.

When pressing PLAY: The mechanical tape transport seems to work. It plays, rewinds and fast forwards.But there's no sound/no output. Not from the headphone jack, nor from the stereo outs or the monitor outs. The mixer led-display ("VU-metering") is totally dark, both when playing back recorded tapes and when set to monitor incoming microphone signals.

Dummy-checks done:
I have the original power supply 12 VDC, and I've also tried another one with
I have tested it with cassettes known to be recorded with sound.
I tried to do a test recording (handclaps) on a used cassette with music on. I took the cassette to play it back on another machine, but no sound had been recorded, neither had any of the old music been deleted (by the 4-track eraser head).

What I have tried:
I opened the machine. It consists of 5 connected circuit boards plus the tape transport unit.

Click the image to open in full size.

A small powerswitch/jack-pcb
A big PCB marked R/P (assuming it means recorder/player)
A big PCB with all the controls on the mixer
A small PCB for the LED Display (VU-meters)
And a long thin stripe with all the different outs/AUX-send-jacks at the top.

Visual inspection tells me nothing, I can't see anything fried or any solder joints loose.
Click the image to open in full size.

Click the image to open in full size.

Click the image to open in full size.

I dismounted the tape transport unit and used an electronic cleanerspray (alcohol based, non-lubricating et) to clean the switches for rec/play etc. (Small copper tongues being pushed together when pressing the buttons for play/rec etc.)
In a similar way I cleaned all jacks, all switches and pots in the machine

When a "noob" thinks out loud:

I am the original owner, prior to this, this machine has never been opened. It has not taken a beating, fallen to the floor or any such thing. It has NOT lived its life in a dust free environment. Oxide or dust seemed like a good place to start.

Why doesn't the green power LED remain lit when the power is turned on?
- Is there something broken in the power-on switch on the back?
-

Why is there no sound when a tape is playing?
- Is the playback head not getting any "power"?
- Is there some broken link between the mixer/output section and the recorder/player?

Resources:
I do not have the service manual and haven't been able to find one.
I have soldering gear and a Multimeter.


Thankyou very much for reading. If anybody has tips or ideas on checks I can do I would very much appreciate it.

Cheers,

Carl
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Old 2nd May 2014, 09:59 AM   #2
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Well, hi!
If the Led doesn't light...what about checking from the power supply input to the regulator ? I see the Pitch is the pot near the heatsinked ( !?) transistor, so that's not a 9 V tension regulator...nevermind.
So the only tension available is the one that powers the motor, the other parts seems to be cutted away from the supply.
You can look at the datasheets of the various ICs and see where the Vs is applied, so test if they get the right supply.
You could divide the two PCBs and try each one indipendently ( easy to say !!)
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Old 2nd May 2014, 10:53 AM   #3
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Quote:
Originally Posted by picowallspeaker View Post
Well, hi!
If the Led doesn't light...what about checking from the power supply input to the regulator ? I see the Pitch is the pot near the heatsinked ( !?) transistor, so that's not a 9 V tension regulator...nevermind.
So the only tension available is the one that powers the motor, the other parts seems to be cutted away from the supply.
You can look at the datasheets of the various ICs and see where the Vs is applied, so test if they get the right supply.
You could divide the two PCBs and try each one indipendently ( easy to say !!)

Hi there,
Thanks for chiming in. I'll look into your suggestions! I also emailed Fostex to see if they can send me a Service Manual.

Here is the Power-PCB, if it provides any more clues. Thanks again!/C

Click the image to open in full size.
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Old 2nd May 2014, 10:55 AM   #4
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BTW, if there are any other closeups that would give you a better view - please tell me and I'll shoot my best.
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Old 2nd May 2014, 11:16 AM   #5
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Hi,
That's what I thought: the wall adaptor provides 12V AC and not DC as you stated, right? Because that seems to be providing dual voltages from a single bipolar AC source.

Last edited by picowallspeaker; 2nd May 2014 at 11:23 AM.
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Old 2nd May 2014, 11:37 AM   #6
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That looks like it could be a regulator on the heatsink, I'd check the supplies around the reg.
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Old 2nd May 2014, 11:37 AM   #7
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No, it runs on DC. The original power supply gives 12VDC, 600mA, positive center polarity.
The machine also states that it wants 12 VDC on the back.

Thanks/C
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Old 2nd May 2014, 11:47 AM   #8
Mooly is online now Mooly  United Kingdom
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Jumping in with both feet first

What is the DC voltage across each of the large caps on that little PCB ?

The device on the heatsink has been mentioned. What is the device type ? What is the voltage on all three pins (be very very careful not to short any out)

What is the device marking on the IC below that heatsink (the long black IC) ?
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Old 2nd May 2014, 11:50 AM   #9
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Here are closeups of the heatsink next to the Pitch-pot.

Click the image to open in full size.


Click the image to open in full size.
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Old 2nd May 2014, 11:53 AM   #10
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Hi!
Thanks all newcomers for chiming in. Like I tried to explain in my introducition I am truly a newbie. I can solder a loose joint, or follow instructions such as soldering small circuits (guitar fx-pedals) but this is my first adventure in electronics troubleshooting.

So this is the kind of newbie I am:
When measuring voltage, I measure from each leg to ground, right?

Thanks for your interest (and patience)
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