Akai GX-400D-SS / GX-400D issues

[surround.sound.enthusiast]

I have an Akai GX-400D-SS that's developed a problem. When I bought it I tested all of the controls for function, and it worked fine,
as far I could tell without a tape. I torn it down to replace the broken nylon shaft on the right tensioner arm (common failure), and
to deoxidize the switches while I was there (Deoxit D5 and Gold G5). I just got the new shaft and installed it, and proceeded to put
the rest of the deck back together.

This is where the problem reared it's head; as soon as the two power switches are engaged the tape deck begins forward play on the
capstans alone, and at whatever speed happens to be selected on the front panel. The solenoids for the reel tables, pinch rollers and
head assembly are not being energized (when I manually engaged the table mechanisms, they turned in time with the capstans). The
play control switches on the front panel do not respond (or light), and the relay on the servo control board does not remain latched
(I'm expecting that it's supposed to).

I have some concern that the Deoxit may have soaked into a circuit board and is causing the fault, but I deoxidized 4 or more weeks
ago and it's been sitting unplugged since. I have further concern that it may have done some sort of desolving action somewhere
causing the fault. I read around the forum, and read that cold or shorting solder joints has been known to be a problem on Akai reels.
Does anyone have any suggestions on what my problem might be?

 

[DuncanS]

Have you a circuit schematic diagram you can attach? I've an Akai GX-635 from the same era (sadly stereo!) and looking at the schematic all the control functions go through a M54410P IC, the outputs of which drive all the solenoid circuits and LEDs, including some logic ICs. My gut feeling is that its not your cleaning fluid.

 

[surround.sound.enthusiast]

I do, but it's part of the service manual, which is a bit too large for attaching to the message chain. A copy can be downloaded at www.hifiengine.com I don't think my problem has to do with the deoxidizing chemicals, but I have read elsewhere about some circuit board material not taking well to deoxiding chemicals, so my worries strayed there about the switches and boards.

 

[DuncanS]

I do, but it's part of the service manual, which is a bit too large for attaching to the message chain. A copy can be downloaded at www.hifiengine.com I don't think my problem has to do with the deoxidizing chemicals, but I have read elsewhere about some circuit board material not taking well to deoxiding chemicals, so my worries strayed there about the switches and boards.

I've downloaded the manual with the schematic, the plus side is its an all transistor design so it will be repairable, proprietary ICs are obsoleted after they stop manufacturing units. All the control circuitry runs from a 24V DC power supply, check to see if that's present, the motors are AC which is why they function.

..and thanks for the site link, I'd never found that, so I've downloaded manuals/schematics for my 4000DS, GX-635D, and DTC-690.

 

[surround.sound.enthusiast]

This is a v-e-r-y late update, but I got straightened out on my GX-400D-SS issues in early 2017. I was advised that on this model the capstans will begin turning when the power is applied, and that the pinch rollers do not engage unless the tension arms are in the tape loaded positions. Once these conditions are met, the playback control fully functions. It was all down to unfamiliarity with open reel tape decks on my part, not age or damage. The upside was getting the entire unit looked over and serviced where needed, and reverse engineering the contactor pin and spring (that I did not know was missing from the broken right tensioner arm). It all worked great after that. Thanks DuncanS for chatting with me back then.

 

[DuncanS]

This is a v-e-r-y late update, but I got straightened out on my GX-400D-SS issues in early 2017. I was advised that on this model the capstans will begin turning when the power is applied, and that the pinch rollers do not engage unless the tension arms are in the tape loaded positions. Once these conditions are met, the playback control fully functions. It was all down to unfamiliarity with open reel tape decks on my part, not age or damage. The upside was getting the entire unit looked over and serviced where needed, and reverse engineering the contactor pin and spring (that I did not know was missing from the broken right tensioner arm). It all worked great after that. Thanks DuncanS for chatting with me back then.

Funnily enough I've had my GX-635D & 4000DS serviced since then, cost well over £500 and sorted out all the mechanical issues I had with them, it was worth it! For those in the UK and probably Europe I'd recommend http://www.servicesound.com/ for servicing Reel-to-Reels.