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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 27th Jul 2020, 3:15 pm   #21
Boulevardier
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Default Re: Akai 4000DS, oscillator problem, any help?

" the PDF version of SM I have is very unclear and I cannot tell the difference between a cross over and a connection."

I agree, the PDF is very unclear on those crossovers and junctions; even when magnified the junctions are pretty well indistinguishable from crossovers without resorting to circuit analysis. Why oh why don't we all still use those little loops to show where a wire crosses another without connecting to it?

Mike
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Old 27th Jul 2020, 3:21 pm   #22
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Default Re: Akai 4000DS, oscillator problem, any help?

On the schematic, P11....bottom left pin.....first intersect = dot......That's it for that section.

Lawrence.
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Old 27th Jul 2020, 3:36 pm   #23
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Default Re: Akai 4000DS, oscillator problem, any help?

Quote:
Originally Posted by ms660 View Post
On the schematic, P11....bottom left pin.....first intersect = dot......That's it for that section.

Lawrence.
That's the one that foxed me, Lawrence, until I realised it just had to be a junction and not a crossover. If not, then the RH record head would be in series with the erase heads! Criminal negligence on the part of the draftsman, I reckon!

Mike
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Old 27th Jul 2020, 3:57 pm   #24
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Default Re: Akai 4000DS, oscillator problem, any help?

Thanks Larry, or do you prefer the full Lawrence?
I guess it would be best to keep it to Lawrence to forestall complications.
That has cleared up all the mess in that circuit.

Larry
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Old 27th Jul 2020, 4:33 pm   #25
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Default Re: Akai 4000DS, oscillator problem, any help?

No it was just the pictorial view of the switch from the assembly drawing.

I think all the PDF versions of the 4000DS SM I have suffer from that issue, will double check later.

David
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Old 29th Jul 2020, 4:20 pm   #26
Larry4911
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Default Re: Akai 4000DS, oscillator problem, any help?

Ok, I did some more probing around the oscillator board and found an anomaly. The collector of the 2sc1098 does not have 43 volts on it as stated in the schematic it has 15v as does the emitter. I guess I've blown it. Oh well, now to hunt for a suitable replacement.

Larry
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Old 29th Jul 2020, 8:35 pm   #27
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Default Re: Akai 4000DS, oscillator problem, any help?

Hi Larry,

To be absolutely sure it is TR 1 (apart from measuring its junctions when out of circuit) make sure you have the 40 odd volts output from the rectifier circuit feeding into R3.

Many alternatives for the 2SC1098, quite a few 2SC1098 on eBay, some at silly prices.

I have previously used 2SD361 (similar spec as the 2SC1098 but lower V CBO) which is an equivalent for the 2SC1096 as used in the 4000DS Mk. II for TR 1. I should have a spare 2SD361, let me know if you are struggling to find a replacement and I will post it to you (assuming I can find it).

David
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Old 3rd Aug 2020, 8:00 pm   #28
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Default Re: Akai 4000DS, oscillator problem, any help?

For reference purposes, I scope measured erase and record bias voltages at the heads of one of my 4000DS Mk. 1 (Serial # S-71103-00077), all voltages are nominal peak to peak. Did 3 measurements (at each head wire) switching the Track Selector Switch to its 3 positions of Stereo, 3-2 and 1-4

Erase Head White wire :- Stereo =96V, 3-2 = 20V, 1-4 = 108V
Erase Head Red wire :- 190V in all 3 positions of the Track Selector Switch
Erase Head Blue wire :- Stereo =96V, 3-2 = 80V, 1-4 = 200V
Erase Head Black wire :- 0V in all 3 positions of the Track Selector Switch

Record Head Green wire :- Stereo = 0V, 3-2 = 18V, 1-4 = 0V
Record Head Pink wire :- 16V in all 3 positions of the Track Selector Switch
Record Head Red wire :- Stereo =15V, 3-2 = 15V, 1-4 = 0V
Record Head Black wire :- 0V in all 3 positions of the Track Selector Switch

All results on the Record head are lower than the 11V rms stated in the manual, for the Erase head some results are lower and some are higher than the stated 52V rms in the manual.

I find some of the voltage results confusing.

Frequency was a nominal 104.16kHz (F = 1/T calculated from 9.6uS), there were some very minute changes in frequency depending upon Track selection Switch position and head connection.
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Old 10th Aug 2020, 7:27 pm   #29
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Default Re: Akai 4000DS, oscillator problem, any help?

Well, I've rewired the track selector switch, thanks for the assist, and ran a couple of tapes through to make sure my wiring is good. I'm glad I took the switch to bits now as the contacts were really badly oxidised and I had to polish them to get a good contact. Stereo and mono tapes play fine. It may be the placebo effect, as I did it, but the fidelity sounds greatly improved.
Now all I need is some calibration tapes as I'm sure I messed up the level pots on the amp board.
Anyone know how to setup the levels with no proper tapes?

Thanks again for the help.

Larry
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Old 10th Aug 2020, 7:35 pm   #30
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Default Re: Akai 4000DS, oscillator problem, any help?

DMcMahon: that's interesting, do you know what the 71103 at the beginning of the serial number is? Possibly date? 3rd Jan 1971? Or 1st March 1971? Would those dates make sense from the dates of manufacturing?

Larry
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Old 10th Aug 2020, 9:04 pm   #31
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Default Re: Akai 4000DS, oscillator problem, any help?

I have wondered before if the Akai serial number includes any date information but I do not know.

1971 is maybe a year or two too early for first 4000DS MK. Is

If the first part is the date then one would assume that 00077 was the actual serial number.

However look at attached from another of my Mk. Is which shows S-80407-00777. The 80 (if a year) would be a little to late as the Mk. Is finished production around 1978.

Maybe a co-incidence but 00077 for one and 00777 for the other ?

I will check out some of the my other Akai serial numbers.

David
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Old 10th Aug 2020, 9:59 pm   #32
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Default Re: Akai 4000DS, oscillator problem, any help?

Be aware of the Japanese method of era dates - this machine is in the Showa era.

4000D available in 1971, 4000DS in late 1972, replaced by 4000DS MkII late 1973.
Later versions for UK market have a plastic head cover, the 50/60Hz pulley and switch,
and also the voltage selector were omitted.
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Old 11th Aug 2020, 10:56 am   #33
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Default Re: Akai 4000DS, oscillator problem, any help?

That is interesting, do you think the S at the beginning of the serial number denotes Showa ?

David
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Old 12th Aug 2020, 12:15 pm   #34
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Default Re: Akai 4000DS, oscillator problem, any help?

Quote:
Originally Posted by Boulevardier View Post
" the PDF version of SM I have is very unclear and I cannot tell the difference between a cross over and a connection."

I agree, the PDF is very unclear on those crossovers and junctions; even when magnified the junctions are pretty well indistinguishable from crossovers without resorting to circuit analysis. Why oh why don't we all still use those little loops to show where a wire crosses another without connecting to it?

Mike
Not great quality but I think a little bit better is this extracted section from the 4000D schematic.

David
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