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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 16th Jan 2022, 2:19 pm   #1
petechunnie
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Smile Akai 4000DS. R2R record mechanism not functioning.

Hello everyone, a recently engaged enthusiast of 1970s Hi-Fi equipment I have sourcing various components and have acquired an Akai 4000ds. After searching threads over the globe I've not found a problem solving/service checking process to narrow down and determine the 'recording mechanism' failure fault to then fix.
I am new at this for sure but have learned recently to solder, recap circuit boards and am happy to work my through the many other skills as necessary (within reason) to restore these and service (at least my own items) as required.
Would anyone be able to suggest a starting place or direct me I have pulled my deck apart (which is still in functioning state for testing) & am stuck as to what to do next. Any guidance/sharing I would be grateful. Cheers pete::
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Old 16th Jan 2022, 2:48 pm   #2
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Default Re: R2R record mechanism not functioning

Welcome to the forum.

I've got one of these, can you give some more details? Does it play back a pre-recorded tape? If you make a recording, do the VU meters move? Have you tried using headphones?

These are great domestic reel to reel decks with long lasting heads, the only problem with them is the mazac cams which can crumble away.
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Old 17th Jan 2022, 12:39 am   #3
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Default Re: R2R record mechanism not functioning

A couple of questions in addition to Kens:

When you go into record, does the record light come on?

When you go into record, does it erase previous recordings?

As Ken has already said, one of the problems with these machines is that the cams that operate different mechanical functions break up. It could be that the record cam has already done so.
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Old 17th Jan 2022, 10:49 pm   #4
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Default Re: R2R record mechanism not functioning

Quote:
Originally Posted by Michael Maurice View Post
A couple of questions in addition to Kens:

When you go into record, does the record light come on?

When you go into record, does it erase previous recordings?

As Ken has already said, one of the problems with these machines is that the cams that operate different mechanical functions break up. It could be that the record cam has already done so.
There isn't a record cam on these, the switching is carried out by a wafer switch on the play/record lever shaft. The record button simply removes a mechanical stop on this shaft, a symptom of the cams breaking up is not being able to engage play or wind or being able to engage both at the same time. Worry not too much about the cams though, replacement cams are available made out of aluminium billet or plastic both are easy to fit although I did find the aluminium one needed a bit of filling before it fitted.
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Old 18th Jan 2022, 12:27 am   #5
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Default Re: R2R record mechanism not functioning

I beg to differ:

The switch you are referring to is the track selector.

There are two cams on top and two underneath. One of the cams underneath operates the 'flipper' and moves the idler into the FF position, the other is the record cam, when you move the play/rec knob into the record position, the cam operates a lever which switches the bias oscillator and the record light on.
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Old 18th Jan 2022, 11:31 am   #6
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Default Re: R2R record mechanism not functioning

Quote:
Originally Posted by Michael Maurice View Post
I beg to differ:

The switch you are referring to is the track selector.

There are two cams on top and two underneath. One of the cams underneath operates the 'flipper' and moves the idler into the FF position, the other is the record cam, when you move the play/rec knob into the record position, the cam operates a lever which switches the bias oscillator and the record light on.
Not on the 4000DS that is sitting just 3 feet away from me as I type this!
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Old 18th Jan 2022, 4:17 pm   #7
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Default Re: Akai 4000DS. R2R record mechanism not functioning.

Gidday To All, thanks so much for your comments & the welcome.

Ok it was all working for prob 2yrs. Then I noticed when I hooked it up tot Sansui QRX7700 it didn't seem to record. I thought I had connected or incorrectly. But after many weeks and trying a secondary amp alas there is a problem.
I thought well I'll give it a.good service, find the fault and fix it. The red light was working now it's not. I will check the bulb but pretty sure it's.fime. not knowing much about this I obtained a manual and service manual but cannot reference a process to check and find the fault. It would appear that the mechanism is not shifting onto place all the way perhaps? Best guess. All other functions are working fine. I can playback, rewind, FF etc. I tried different reels and speeds all Worx fine. VU meters perfect. There was an anomaly where I the UV meters were randomly spiking which I thought was the recording issue somehow. After a thorough clean they are normal again.
The heads were very dirty, but all cleaned including, guides, rubbers you name it all good.
I really just know what my next move is now...over to all again...thanks in advance
Pete

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Old 18th Jan 2022, 8:58 pm   #8
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Default Re: R2R record mechanism not functioning

Quote:
Originally Posted by Analogue man View Post
Quote:
Originally Posted by Michael Maurice View Post
I beg to differ:

The switch you are referring to is the track selector.

There are two cams on top and two underneath. One of the cams underneath operates the 'flipper' and moves the idler into the FF position, the other is the record cam, when you move the play/rec knob into the record position, the cam operates a lever which switches the bias oscillator and the record light on.
Not on the 4000DS that is sitting just 3 feet away from me as I type this!
Can send me some pictures of the back of the switches? ie around the part near the flywheel?
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Old 18th Jan 2022, 9:29 pm   #9
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Default Re: Akai 4000DS. R2R record mechanism not functioning.

In the manual I'm looking at the record/Playback switch is operated by a small pear shaped cam on the part of the Record/Playback selector shaft that's below the switch table, it shifts the lever and thus the link spring/rod that's connected to the Record/Playback switch.

Lawrence.
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Old 18th Jan 2022, 10:09 pm   #10
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Default Re: Akai 4000DS. R2R record mechanism not functioning.

Quote:
Originally Posted by petechunnie View Post
I thought well I'll give it a good service, find the fault and fix it. The red light was working now it's not. I will check the bulb but pretty sure it's fine. not knowing much about this I obtained a manual and service manual but cannot reference a process to check and find the fault.
Pete
Unfortunately fault finding information in service manuals is often poor/not very helpful to non existent.

Unlikely to be the bulb, if it does not erase a previous recording (do not think you have answered this previous question) then that would indicate that it is either not correctly being switched to Record mode or a fault with the bias oscillator circuitry.

David
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Old 18th Jan 2022, 10:52 pm   #11
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Default Re: Akai 4000DS. R2R record mechanism not functioning.

I think the 2 different cam configurations being discussed is the difference between the Akai 4000DS models (and other similar models) and the Akai GX-4000 models.

David
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Old 19th Jan 2022, 12:33 am   #12
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Default Re: R2R record mechanism not functioning

Quote:
Originally Posted by Analogue man View Post
There isn't a record cam on these, the switching is carried out by a wafer switch on the play/record lever shaft.

There is not a wafer switch, the assemblies on both the Play/Record shaft and the FFD/RWD shaft which look like switch wafers are mechanical ball bearing detent mechanisms.

There is a Record cam, in the documentation it is called "Amp switch cam B" Item 30, as Laurence also describes it actuates the PB/Record switch SW9.

Photo 1 shows the PB/Record selector in the Off Position.

Photo 2 shows the PB/Record selector in the Play position, the cam has rotated.

Photo 3 shows the PB/Record selector in Record position, the cam has rotated further and actuates SW9 via the various levers.

David
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Old 19th Jan 2022, 11:38 am   #13
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Default Re: Akai 4000DS. R2R record mechanism not functioning.

Photo 2 in my Post 12 above is incorrect for the Play position, it actually shows the Record position the same as Photo 3.

Correct photo 2 is attached to this post showing the Play position where the cam has rotated from its vertical position shown in Photo 1 above, it makes light contact with the white cam roller but does not move the Record levers (may make them pulse a little).

Photo 4 partially shows the PB/Record slide switch SW9 below the 6 way connector, this is in the bottom left of the PCB when looking from the rear.

Photo 5 shows the L shaped sprung loaded record lever (note the service manual shows a large spring here) which has a vertical tab that actuates SW9, so important for the OP to make sure that when switched to Record that the tab is mechanically actuating SW9.

David
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Last edited by DMcMahon; 19th Jan 2022 at 11:44 am.
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Old 19th Jan 2022, 11:54 am   #14
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Default Re: Akai 4000DS. R2R record mechanism not functioning.

Quote:
Originally Posted by petechunnie View Post
The red light was working now it's not. I will check the bulb but pretty sure it's.fime.
The Record lamp is connected to the 5 Volt winding on the mains transformer via one of the changeover contacts on the Record/Playback switch (SW9)

Lawrence.
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Old 19th Jan 2022, 3:22 pm   #15
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Default Re: Akai 4000DS. R2R record mechanism not functioning.

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Originally Posted by DMcMahon View Post

Photo 4 partially shows the PB/Record slide switch SW9 below the 6 way connector, this is in the bottom left of the Power Supply & Oscillator PCB when looking from the rear.


David
Edit update above in bold italic.

David
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Old 19th Jan 2022, 3:43 pm   #16
petechunnie
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Default Re: Akai 4000DS. R2R record mechanism not functioning.

Hi All,
ok I have pulled the inner frame out and have managed to get both the record func and record light to operate. I didn't have time to try a recording I will do that this weekend. I do suspect the issue still remains as this is what initially got me puzzled, as it all appears to be operating correctly, VU meters working on source when in record pause mode, then nothing on the tape. I suspect its erasing and not recording (not sure how to correct this, reading the manuals etc but i dont get it) or its this oscillation issue. Im keen to go again on the weekend to see if I can run all sorts of checks etc.
Questions: I noticed the belts are loose, sloopy, not taunt as I would have thought...should they be? Where can I obtain a couple of them from? Lastly do I need to acquire an oscilloscope to finish this off properly? If so what would you recommend they get up there but figured there's most likely a middle of the road unit that may suit the novice enthusiast.

Thank you all again very much!
ps how did you attach the thumbnails David?
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Old 19th Jan 2022, 3:58 pm   #17
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Default Re: Akai 4000DS. R2R record mechanism not functioning.

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Old 19th Jan 2022, 5:44 pm   #18
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Default Re: Akai 4000DS. R2R record mechanism not functioning.

Quote:
Originally Posted by petechunnie View Post
Hi All,
I suspect its erasing and not recording (not sure how to correct this, reading the manuals etc but i dont get it) or its this oscillation issue.
If you have an existing recording on tape then just select Record (does not need a record signal connected) and run the tape over a section of the existing recording.

If erase is functional then the existing recording should be totally erased when you play back the tape.

David
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Old 19th Jan 2022, 6:01 pm   #19
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Default Re: Akai 4000DS. R2R record mechanism not functioning.

Quote:
Originally Posted by petechunnie View Post
Questions: I noticed the belts are loose, sloopy, not taunt as I would have thought...should they be? Where can I obtain a couple of them from? Lastly do I need to acquire an oscilloscope to finish this off properly? If so what would you recommend they get up there but figured there's most likely a middle of the road unit that may suit the novice enthusiast.
The tape counter belt can be quite loose/sloppy and often the counter will still work fine.

The capstan belt should be reasonably snug, if the belt looks in good condition and playback sounds OK (i.e. speeds sound OK/Wow & Flutter not bad) and it fast winds in both directions end to end of the tape then the belt does not need changing.

Various online sellers such as eBay will sell the appropriate drive belts set.

For people that use oscilloscopes (myself included) the oscilloscope is an invaluable diagnostic tool, but you need to have a reasonable idea how to use it for it to be beneficial.

If the Bias oscillator circuit is faulty then an oscilloscope is the ideal piece of test equipment to check it out. Due to the bias signal being high (relatively) frequency run of the mill DVMs/DMMs will not accurately be able to measure the bias signals.

At this stage I would say a scope is not required. First need to establish if erase is working. If erase is working then the record bias should be good.

David
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Old 19th Jan 2022, 6:36 pm   #20
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Default Re: Akai 4000DS. R2R record mechanism not functioning.

By removing the right hand side panel (has mains transformer etc fitted to it) one can view the PB/Record switch SW9 better.

Note - if panel is removed then when refitting have to be careful that the end of the record lever (copper looking riveted plate) does not drop on the outside of the record lever that slides horizontally.

The 2 record levers shown in the photos are shown somewhat different in the service manual, the sliding lever is shown as a spring and the vertical lever with the riveted plate is shown as a different lever with a piece that screws onto it. My photos are for the 4000DS Mk. II, not sure if the 4000DS Mk. 1 or the 4000D/DB are the same as the MK.II or whether they match the service manual, I will check my other recorders later.

David
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