Akai 4000D arrived today

[DMcMahon]

Excellent job on the heads Garry and well done with the Reel Table clutch adjustments.

[garry71]

Originally Posted by TIMTAPE

Yes I've found in machines showing obvious signs of corrosion, their tape head faces are often also corroded.

That aside, with the quarter track format, when the heads develops a wear groove as yours have looking at the photos, the left channel is usually the one to drop off first because it's hard up against the "corner" of the wear groove where dirt accumulates. The dirt lifts the tape off the pole piece. The right channel is nowhere near the bottom "corner" of the wear groove and so doesn't clog as easily.

Many pro machines and some better consumer machines such as Revox and Uher used heads with "gutters" or "relief slots" cut into the head faces just either side of the tape path, so even with head wear, corners couldn't develop.

Thanks for the information.
When I was looking at the heads, I thought to myself "I bet I can guess which one is the left channel!"

[garry71]

Originally Posted by DMcMahon

Excellent job on the heads Garry and well done with the Reel Table clutch adjustments.

Thanks for that!
One thing I noticed is that when you pull the mono switch out, it doesn't combine the stereo inputs together, so I may make a modification with an extra switch to give that option.

Do you know what size the threads are for the front panel screws? I tried a 3mm and it was too big. Measuring an original screw it was 2.85mm, so it might be an imperial thread size.

Cheers

[garry71]

I put it all back together the other day, had a couple of hours out of it, then the right hand channel on stereo stopped recording. It erases but doesn't record.

In the various mono settings the right hand side records via the left channel circuits, so it's most likely a fault on the right hand record pcb.

Does anyone know of any common faults to look out for?

I need to open it up again soon anyway; The feed clutch could do with tightening up a tad, and the take up clutch has a regular squeak each revolution when in PLAY.

[stacman]

Could be the 2SC458LG transistors on these, notorious for going noisy, I have the GX4000 version and changed them in the amplifier section, try a google search for akai 4000 noisy transistors, various links, including some to this site, equivalents are available, also the selector switches need a good servisol clean.

[garry71]

I've already cleaned all the switches with servisol, so I'll swap the left and right boards around and see if the problem moves across.

Cheers

[DMcMahon]

Are there separate left and right boards in the 4000D ?

[garry71]

Yes, there are four small boards; play back right, record right, and the same for the left. They're in a vertical side section, and pull out on edge connectors.

I swapped the right and left record boards and the problem moved over to the left, so the right channel board is knackered.

I've ordered two refurbished record boards from ebay for 20 quid posted. I'll put those in and can compare the other two as a fault finding excercise, and probably put new transistors in.

[DMcMahon]

That is good. Have never had to look at mine in the 4000D. I think all the other 4000 series have the one main Pre-Amp board, so the 4 separate boards is like some of the later Akai's.

I can now actually see the 4 boards in the 4000D schematic as attached.

[DMcMahon]

I obviously have looked at mine because I have photos ! memory !

[garry71]

There's a much better quality scan of the diagram on the net, should you ever need it. It's at the end of the user manual on hifi engine.

https://www.hifiengine.com/manual_li...ai/4000d.shtml

[garry71]

Originally Posted by DMcMahon

I obviously have looked at mine because I have photos ! memory !

It's a well laid out machine, I think, and the schematic is fairly easy to work with as all the cable colours are noted down.

[DMcMahon]

Yes I have the User Manual scan, just attached the other schematic because it is not cut into 2.