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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 30th Oct 2018, 5:22 pm   #1
g0hze snowy
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Default Akai 4000DS Mk-II

Hi All, I have the above reel to reel tape recorder/player.
My problem is no record on left channel, right was ok, all the voltages appear correct, plays pre-recorded tapes.
Various recommendations about changing the electrolytic caps have been done, the 2sc458 trannies have been removed and tested, all ok, I have new replacements just in case 1 fails as have the other trannies on the record/playback pcb board.
The main oscillator board has been removed, caps changed and sockets and switches cleaned with 'deoxit'!, now no record on either channel, so I undid all that I had done but still no joy.
I hope it is not the record head as it would make the unit BER.
It is the limited all black edition, 1 avenue is to look for a cheap damaged item and make a good one up out of the 2,
unless
one or some of you learned gents know better.
Any help/advice greatly appreciated.
cheers
Snowy
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Old 30th Oct 2018, 5:37 pm   #2
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Default Re: Akai 4000DS Mk-II

Hi Snowy , before doing any of the above , i would have traced a signal through it , i.e. was it getting to the input amp , then is it getting out or there and into the osc, then is it getting out of the osc to the head etc , I would check the wiring now and make sure its all back where it should be and that all new caps are orientated correctly also check your soldering ( im not assuming its poor , i do it all day and i still manage to make little bridge errors some times ) , if you have checked and checked , check again. lol...and then when you are 100% certain you have everything as it was trace an input signal though it (assuming you have a scope/tracer) and see where you loose it . A sine wave is useful here , if you dont have a signal generator , you can use an app on a phone to generate one i should think these days .
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Old 30th Oct 2018, 7:23 pm   #3
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Default Re: Akai 4000DS Mk-II

Thanks for the advice Norfolk Dave.
I have a Farnell lm3 or 4, or maybe both!, so I will try your advice tomorrow, the solder bridges was the 1st thing I thought I had done so board out and checked, no luck, is that right, anyway no bridges found.
What made me realize I had a problem is when I saw that the meter needle wasn't bouncing up and down as was the right meter, I had the switch in the source not the tape position.
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Old 30th Oct 2018, 7:53 pm   #4
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Default Re: Akai 4000DS Mk-II

Unlikely the record head has failed - each side should measure 15 ohms, about 15mH.

It sounds like you have no bias oscillator - can you still erase a previous recording ?
You could detect the bias signal across the erase head with a meter or even a neon bulb.
Failing this, listen to the second harmonic on a long wave radio - it will sound as an
unmodulated carrier.
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Old 30th Oct 2018, 8:32 pm   #5
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Default Re: Akai 4000DS Mk-II

restoration 73, thanks for the advice, I am assuming that I do have the bias oscillator as all the voltages are within a few mV of what the schematic shows, The problem seems to stem from when I 'Detoxit'ed the 5 way connector and record switch, so everything dried off with looooong ear cleaner type buds. Anyway I have a few things that I can now check thanks to the suggestions.
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Old 30th Oct 2018, 9:32 pm   #6
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Default Re: Akai 4000DS Mk-II

Right some test results obtained, record heads measure 7 ohms on each coil, I injected a 1 and 3kHz tone from 1 side of the heads and heard it thru' my head phones on record, both meters showed the same amount of movement.
record transformer showed continuity thru' the 3 x windings
measured the continuity between the playback/record switch no problems there, so desoldered it and resoldered it as there was a surplus of solder around the contacts.
play back of pre-recorded ok, erase ok.
as stated before all voltages are within limits.
not sure what else I can do now.
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Old 30th Oct 2018, 10:26 pm   #7
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Default Re: Akai 4000DS Mk-II

I’m with restoration on this one, Ideally you need a scope to check the bias both on the erase head and record head.

One thing you may have overlooked is the track selector on top of the head block, give it a good clean with De-oxide.
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Old 31st Oct 2018, 12:17 am   #8
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Default Re: Akai 4000DS Mk-II

Cheers MM, I will do that tomorrow, as well as the (apparent) problems with the mic sockets that I have been advised to check.
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Old 31st Oct 2018, 11:46 am   #9
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Default Re: Akai 4000DS Mk-II

Good Morning Gents, well some success, I have narrowed the fault down to the mic sockets, detritus, muck, accumulation of many years of dust and possibly smoke.
cleaned as best I could and so now I have both channels recording.
left meter needle a little lower than its mate but I can live with that for the moment.
so 2 x questions for you.
1. how do I get them out of the block that they are mounted in, I have them out of the machine no problem, they just seem to be a permanent fixture in said block.
2. has anybody changed them out and replaced them with what?, they seem to be commonal garden type mono sockets, don't think there is enough room for a nut mounted type, the nuts would foul the front panel as they appear to be a flush fit.
Thanks everybody for the help and advice so far, just a little further to go please.
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Old 1st Nov 2018, 4:12 am   #10
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Default Re: Akai 4000DS Mk-II

The mic sockets should not affect recording through the line in (phono) sockets, the
switch on them just breaks the input connection from the 5 pin DIN socket.
This type of socket is still available on the web, and the stereo type with break switch
often used for stereo headphones will work fine on mono with only the tip contact used.
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Old 1st Nov 2018, 9:13 am   #11
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Default Re: Akai 4000DS Mk-II

Hi Resto'73
I really am going to blow up the schematics on this thing, I could have sworn ( I did several times but at another item) that there was a joint shown on the print.
The only other thing I did whilst doing the mic sockets was to spray 'de-toxit' into the stereo/mono switch and operate that a few times, maybe--------!.Needless to say it is working, for the moment.
I have even thought about de-soldering the mic sockets and ultra sonic cleaning them, not sure of what the outcome would be doing that, might work or I might end up with a pile of plastic!.
Nowt going to get done today, Thursdays is visit mum in London day. On a good day that's a round trip of 7 hrs with an additional 4 or 5hrs sitting with mum.
So tomorrow it is then.
Thanks for pointing out my error.
Regards
Snowy
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Old 1st Nov 2018, 1:47 pm   #12
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Default Re: Akai 4000DS Mk-II

I had a very similar problem on my 4000DS MK2, no record on one channel. Turned out it was a very simple fault - a cracked solder joint (earth side) on one of the line in phono sockets on the rear of the machine. The crack was tiny and difficult to see but re soldering it fixed the problem.
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Old 1st Nov 2018, 10:44 pm   #13
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Default Re: Akai 4000DS Mk-II

Thanks for your input monaro0162, something for me to check tomorrow.
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