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Akai 4000db motorboating

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Oceanotter

New Member
Greetings!

I picked up an akai 4000db on ebay a few weeks back that was cleaned but had some electrical issues otherwise it all functions normally.

When I first got it the left channel wouldn't record until the machine had been powered on for awhile but it played back fine and there's this consistent popping or "motorboating" as I'm told in the signal. It sounds worse on the right than it does on the left.

Since then I've recapped the preamp, the recording preamp (dolby pcb), the power supply also. I've also replaced the troublesome transistors and one LD3141 for the left channel (on the right side of the preamp pcb not the side with the transformers) . The belts are new too.

Since I've done this I have motorboating on the right channel when set to source but not on tape. Recording on tape seems to carry the issue through but it doesn't sound as obvious. The left channel has some slight motorboating (pop pop pop pop pop etc...) but it's definitely less obvious.

I'm waiting on my LD3141. Replacements to arrive as I intended to replace them all and just have a completely fresh and newly restored deck to call my own but before I replace them I figured I'd ask if anyone out there might know of anything I should be checking to ensure this motorboating issue goes away as I feel while maybe the ld3141s could be the issue it could also be something else too.

Also! Does anyone know what's up with the 7 1/2 equalizer on this deck sounding like crap? It sounds muddy. Far less bright than the 3 inch eq and I'm wondering if thsts by design or if somethings not calibrated right.

So yeah that's about it.

Motoboarding on left (slight) and right (lots) even after all caps and transistors were replaced except for 3 ld3141s. Shows up monitoring source but not on tape. Shows up in recorded samples but not quite as pronounced.

Bless!
 
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Sorry if this is sounds like a dumb question but you’re plugged in through a tape monitor loop on your amp or receiver, right? If you’re plugged into a regular line level input like aux or cd in then you will get internal feedback that sounds like motorboating whenever you go to source and have the selector set for the tape deck. Unfortunately the tape loop has been eliminated on most modern gear so you have to monitor through headphones plugged directly into the deck and make sure the deck is set to Tape not Source before changing the input selector on your amp or receiver. If you’re using gear with a tape monitor loop and the deck is plugged in through it then disregard.
 
Oh! Actually I'll have to try this tonight. I have a modern receiver plugged into CD but I have an older one with a tape input I'll give a shot tonight. It'd be silly if that was the issue the entire time and hopefully it was.
 
audiojones said:
Sorry if this is sounds like a dumb question but you’re plugged in through a tape monitor loop on your amp or receiver, right? If you’re plugged into a regular line level input like aux or cd in then you will get internal feedback that sounds like motorboating whenever you go to source and have the selector set for the tape deck. Unfortunately the tape loop has been eliminated on most modern gear so you have to monitor through headphones plugged directly into the deck and make sure the deck is set to Tape not Source before changing the input selector on your amp or receiver. If you’re using gear with a tape monitor loop and the deck is plugged in through it then disregard.
Click to expand...


Just tried it and still have the same issue on the other receiver.
 
Only on monitor you say? Might be some grounding issue with the "input" channel maybe. Have you tried several input devices? Or the monitor switch could be bad.
 
Okke 70s said:
Only on monitor you say? Might be some grounding issue with the "input" channel maybe. Have you tried several input devices? Or the monitor switch could be bad.
Click to expand...

I'm getting it when it's flipped to source but nothing on tape but it shows up in recorded audio. Ive only got one input device to test with but I'm starting to suspect it could be some grounding issue indeed. I'll deox the switches and see if that helps after thoroughly exersizing them.
 
On mine half the flip switches where dodgy. Good idea to go over those anyway.

If I connect a mobile phone to some amps it also makes noise. Must be some digital signal, or static. It stops the moment that 'play' is pressed.
 
Thanks for the advice everyone. I'm gonna thoroughly clean all this switches and see where that gets me. And I'll report back!
 
I've solved the issue. Cleaning the switches didn't fix it but it did help reduce the noise. I realized that it might be a grounding issue so I applied a screw driver to the case and voila the noise went away almost entirely. I realized since I didn't have the unit entirely reassembled that might be the case and Lo and behold that did the trick.


Thank you all for your help!
 
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