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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 17th Apr 2021, 6:23 pm   #1
hawkman
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Default Sony FH-7 MKII tape deck TC-78II issues

I have a Sony FH-7 MKII mini component system that I'm attempting to repair/restore. After lucking out in a huge way and finding the missing system cable on eBay, I have been able to power up the unit and take stock of what's working and what isn't.

The tape deck is my current task. This unit came with no belts so I had to figure out from the service manual what was missing, a total of 5 belts including one large capstan belt. I cleaned everything with alcohol.

After belt replacement, I powered up the unit. It now exhibits the following defects:
- Rewind: working but seems quite weak. This part of the mechanism doesn't need any other parts to move, the unit simply engages the motor in reverse.
- FF: starts to work, raises a part of the mechanism internally, then drops it, then starts again to raise it. From the front of the machine, the tape jumps forward a bit, stops, then jumps forward again repeating until stopped.
- Play: Never even really gets going. Makes a small amount of motion but the tape head does not raise.

There are three working parts within the mechanism: the motor and two electromagnets. The first magnet is for "FF, Reverse, AMS" and the other for "Head" according to the manual. All of these probably use a fair amount of power to engage and operate.

My current thought process is that this is an electrical issue - there isn't enough power getting to the mechanism to engage it properly. Let me know if this doesn't sound reasonable.

Question then is, where would you recommend checking and what could possible culprits be?

Thanks in advance.
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Old 19th Apr 2021, 8:29 am   #2
DMcMahon
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Default Re: Sony FH-7 MKII tape deck TC-78II issues

Not familiar with this at all so difficult to advise, it looks quite a complex piece of kit.

Have you tried powering the TC-78 standalone using an external power supply (note the note on linking the ground lines for the signal and power supply circuits) as shown in the service manual, in case there is a problem with the +21V DC supply.

I can imagine that the various cams/gears are small and plastic, so carefully check them for any damage.

David
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Old 19th Apr 2021, 9:19 am   #3
Lloyd 1985
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Default Re: Sony FH-7 MKII tape deck TC-78II issues

I’ve done a couple of these, and have come across these faults with them, can’t remember the cause though! I do remember the FF problem, I’ve also had it on play too, with the head bobbing up and down and never latching in place. There is an electromagnet that holds it in the correct state, if you had to remove it to get the belts in then it might just need a bit of adjustment for it to catch. Be very careful of the gears in these, the plastic has the consistency of hard cheese, and strips the gears if given half the chance! I’ll have to sit down and look at mine again carefully to work out what to do with it again. Even on a working one I’ve found the rewind to be a bit poor.

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Lloyd
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Old 19th Apr 2021, 12:18 pm   #4
ben
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Default Re: Sony FH-7 MKII tape deck TC-78II issues

Could also be that the motor has dirty commutator contacts. Had to strip one down on a Sony turntable of this vintage not long back. Low speed and no torque at all. Also needed a drop of oil on the bearing. After that work, it was transformed!
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Old 29th Apr 2021, 3:10 pm   #5
hawkman
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Default Re: Sony FH-7 MKII tape deck TC-78II issues

Thanks guys, useful advice. I bought a variable power supply and tested the unit directly from it - same situation.

I think the idea of lubricating the motor is going to be my next step. I'll report back.
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