Akai 4000DS Mk1 - Left channel audio only

[deadwax]

I picked up an Akai 4000DS this morning. After solving an issue with the 7.5 ips sleeve being stuck halfway onto the capstan it is happily playing tapes. The main issue is audio is from left channel only. The ‘pull for mono’ rh knob is pushed home but when playing stereo tapes there is only activity on the left VU meter, and when playing mono tapes there is no need to pull the knob. The 2nd track isn’t heard playing backwards (in the stereo switch position). The position of the ‘3-2’, ‘stereo’ and ‘1-4’ was having no effect but is now playing backwards (mono tapes)(after a number of switch position changes) on ‘3-2’ and normally in the stereo and 1-4 positions (as I believe it should). The audio of a stereo tape is not affected by the switch position. There is only audible reaction to the switch being moved between ‘3-2’ and ‘stereo’. There is no audible reaction to moving between ‘stereo’ and ‘1-4’. The only other issue is that the tape counter doesn’t work. I’m handy (motorbike restoration) but not dealt with electronics before (only simple bike electrics). Any suggestions with where to look gratefully received. Regards, Steve.

[deadwax]

Update: in the opening post I said there was ‘no need to pull the knob to play mono’. I’ve since realised its function is probably to play the left channel through both speakers. It does not do this when pulled, however.

[DMcMahon]

Have you checked that the tape counter drive belt is fitted, i.e. not missing or broken ?

If the belt is fitted and not overly stretched then it should drive the tape counter pulley wheel which in turn through the gearing should drive the counter wheels.

Try operating the counter reset button many times and manually rotate the counter wheels, this can help to free up a sticky counter, otherwise IPA spray cleaning may be required. I find these counters do not like being lubricated with oil. The counter assembly is delicate so be careful.

David

[deadwax]

Many thanks. I took the case away to find a very slack belt and very stiff pulley but it freed up nicely with the tiniest amount of lubrication help. Counter working freely now.

[deadwax]

Originally Posted by DMcMahon

I find these counters do not like being lubricated with oil. The counter assembly is delicate so be careful.

David

I didn't mean to ignore your advice re: oil. I even googled what IPA was but I'm of an age where in the hour or so after reading your post to taking the case away I completely forgot the advice not to use oil....

[DMcMahon]

That is good news, well done, one problem you can tick off.

IPA (Isopropanol/Isopropyl Alcohol) is the go to general cleaner for many repair enthusiasts, particularly for tape head/tape path cleaning (some people prefer Methylated Spirits for cleaning heads). The stronger the purity % the better, I generally use 99.9%

For cleaning electrical switch contacts then a electrical contact cleaner spray is generally preferable.

David

[deadwax]

After re-fitting the case I was finally able to undo the very stubborn 1.5mm allen key screw holding the track switch on (a judicious tap on the end of the screw finally released its hold). This machine is remarkably clean. Took the opportunity (after watching a youtube video of servicing this machine) to re-grease the greased points and add a film of oil to the three drive pulley pivot shafts. Is it possible/needed to oil the motor? and if needed do you access the shaft by removing the Philips screw and knurled drive (last picture)? I have some contact cleaner coming tomorrow which will hopefully resolve the dead RH channel. If not then it seems I have to replace the LD3141 IC from reading other posts on the forum.

[DMcMahon]

I find that if the 1.5mm allen key is not worn, then it often is very difficult to get it to fit the Track switch & Pause control cup point grub screws, sometimes have had to file the allen key to suit.

Have never oiled these motors and believe that normally they do not require lubricating.

At the underside of the motor there is a small round cover held on by 2 screws, I do not know what is under the cover, sometimes on similar motors there is a oil reservoir felt under the cover.

Have never removed the knurled drive pulley, the motor pulley sits below the knurled pulley so removing only the knurled pulley I do not think you would get easy access to that end of the motor shaft where it enters the motor body.

The LD3141 ICs suffered more with noise problems rather than hard failures. They are long obsolete and very difficult to find any direct replacements. There are various transistor circuits/boards as replacements for the LD3141.

I would not consider trying to replace the ICs unless actually proven by measurements (such as scoping the IC signals) that the IC (s) are dead. I would first make sure the heads are scrupulously cleaned and clean the Track switch and the Play/Record switch contacts as a starter.

David

[wave solder]

On my Akai 4000DS I also had a missing track problem and it was the track switch, no amount of switch cleaner would cure it. The only solution was to give the switch a full strip down, clean and careful lubricate then reassemble.

[ben]

I have seen very noisy track switches on these before.

[deadwax]

Originally Posted by DMcMahon

At the underside of the motor there is a small round cover held on by 2 screws, I do not know what is under the cover, sometimes on similar motors there is a oil reservoir felt under the cover.

I've just watched a video where the guy removed that cover and a couple of small pieces (not clear what they were) and then added a couple of drops of oil whilst spinning the shaft (motor vertical). The problem with youtube etc I guess is that everyone does what they think is needed. In 3 'servicing' videos I've seen 3 different approaches.

[deadwax]

Made some progress last night after a clean of all switches and potentiometers but it didn't last long. Before doing anything I checked whether I had anything on the right channel when recording but even on full input there was only a very low level audio. After cleaning (I did the track switch in isolation first but with no improvement) I managed to get a normal level output from the right channel during play whilst fiddling with the track switch but after a minute or so this failed again. I couldn't replicate it. I tried recording again but had no right channel level. One new thing I noticed (I was only connected as a mono input previously playing the left channel through both speakers so it may not be 'new') was that the right channel is very noisy when the machine is powered up and remains so for a while sometimes. Pulling the 'pull for mono' switch doesn't affect this noise even though it does kill the backwards audio so is working. So am I looking at the track switch as being the most likely culprit or should I look elsewhere? Happy for suggestions as to how to eliminate certain things.

Steve.

[stacman]

Does this model have the notorious 2SC,XXX transistors that are prone to failure in equipment of this age?
Regards, Alan

[deadwax]

Originally Posted by stacman

Does this model have the notorious 2SC,XXX transistors that are prone to failure in equipment of this age?
Regards, Alan

I've just been watching a video where he changed two 2SC458 transistors to solve a noise issue.

[ben]

What did he replace them with? or was it a like-for-like swap?

[deadwax]

Originally Posted by ben

What did he replace them with? or was it a like-for-like swap?

I've got myself slightly confused, on one video he said the problem could be the 2SC458 (replacement 2SC2240) or the LD-3141 IC. He actually replaced the IC to resolve the issue. On another video he did replace the transistors but he didn't confirm which ones but said the equivalent was the 'NPE - 85' (I may have misheard, it was poor audio).

[deadwax]

Originally Posted by wave solder

On my Akai 4000DS I also had a missing track problem and it was the track switch, no amount of switch cleaner would cure it. The only solution was to give the switch a full strip down, clean and careful lubricate then reassemble.

Is this a simple component to remove and strip/rebuild? Did you leave all of the wires attached? I may as well try the same before I resort to replacing components.

[DMcMahon]

Originally Posted by deadwax

I've got myself slightly confused, on one video he said the problem could be the 2SC458 (replacement 2SC2240) or the LD-3141 IC. He actually replaced the IC to resolve the issue. On another video he did replace the transistors but he didn't confirm which ones but said the equivalent was the 'NPE - 85' (I may have misheard, it was poor audio).

There are many online suggested alternatives for the 2SC458, I have used the 2SC2240 with good results, also have used 2SC1845 and KSC1845.

Some of the suggested alternatives have different EBC pinout, so important to compare the pinout of any replacements carefully.

David

[wave solder]

Originally Posted by deadwax

Is this a simple component to remove and strip/rebuild? Did you leave all of the wires attached? I may as well try the same before I resort to replacing components.

It was many years ago so I cannot remember the details. I do know that I did not have to disconnect anything and remember there were some small parts internally that drop out when you dismantle it. But apart from that it was a success (and still works fine).

[DMcMahon]

Have never actually done it but would think it could be pretty fiddly.

David