Akai GX-4000D - no audio from playback head

[O. Friend]

Ok, I just got an Akai GX-4000D reel-to-reel. It’s pretty immaculate, clean as a whistle inside and out (except for some dust on the bottom circuit board). Old grease wasn’t bad, I cleaned that up and put new lithium grease on where needed.
The heads look unmarred, all wiring looks untouched and clean.
The mechanics work like a charm, FF, REW, Play/pause etc. Just a very tiny bit of spill when stopping rewind.

The real issue is, there is NO audio during playback. Zero from the rca outs, nor the headphone out. The VU meters don’t move at all on PB.

When I switch to listen to a source on the line in, it sounds fine, the VU meters move properly, all that looks good. Just nothing from Playback of a tape.

I made sure that the cables from the PB head goes to the proper header on the pcb, as well as the erase and rec heads. I’m including a picture of the wiring, it all looks good. I don’t see any blow components, and the fuses I can see are not blown.

I got the service manual from a couple of sources, but all are unfortunately a bit low rez on the board drawings, so I’m not sure just where to start troubleshooting.

ALSO: If I switch to record from the source, I get no sound when monitoring, BUT it DOES actually record quite well to tape (I move the tape to another unit to test and it was really good). When I choose TAPE MONITOR as it records, only the right meter moves (again, with no sound at the time) but it is recording to both channels.

I’m going to hook the scope up to the wires right at the back of the PB head, but that’s kinda delicate so I thought I’d seek other opinions here.

Thanks for any suggestions!

 

[oldvinyldude]

I don't have specific experience with your model deck, but I can safely say: Clean, clean, clean. Pots and switches, even RCA's-use Deoxit or similar-squirt some into the component, then exercise the switch or pot a few dozen times each. There may also be some leaf switches buried within the unit-I see one switch in your 4th pic. Clean any of those you see.

 

[O. Friend]

Thanks, I have hit all switches with Deoxit and the faders with deoxit fader lube. That record bar switch and a few leaf switches I hit with a few drops of Deoxit as well, and I even cleaned the 3 header connectors (that the wires from the 3 heads connects to the board through) to make sure they were making contact.
I'm wondering if a trim pot on the board might have completely opened, they look a little janky. I'll get the meter on them tonight and see...

 

[Okke 70s]

The large electro-mechanical switch on the PCB is a known weak spot on these. Spraying it from the outside might not suffice. You could check the relevant contacts for continuity, or go by signal tracing.

Having no signal on either side might also indicate a problem in the power supply towards the pre-amp. A quick check on the input voltage there wouldn't hurt.

Signal tracing would probably be the most thorough method, that would also allow you to rule out problems with the head/head contact.

Either way, I hope you two get along because you might be spending quite some time together in the near future

 

[62vauxhall]

A GX4000D I bought and sold a few years ago had the same problem.

Google searching caused me to learn about 2SC458 transistors which I saw referred to as "the bad Akai transistor". I examined the board and sure enougth, there were 14 of them. All of them with black legs cited as a symptom (or cause) of those failed (or about to fail) transistors in Akai components. .

I did not bother trying to identify which of those 14 transistors were dead - just replaced all of them.

The problem was solved. From then on the deck recorded and played splendidly on both channels. .

 

[titanstats]

Ok, I just got an Akai GX-4000D reel-to-reel. It’s pretty immaculate, clean as a whistle inside and out (except for some dust on the bottom circuit board). Old grease wasn’t bad, I cleaned that up and put new lithium grease on where needed.
The heads look unmarred, all wiring looks untouched and clean.
The mechanics work like a charm, FF, REW, Play/pause etc. Just a very tiny bit of spill when stopping rewind.

The real issue is, there is NO audio during playback. Zero from the rca outs, nor the headphone out. The VU meters don’t move at all on PB.

When I switch to listen to a source on the line in, it sounds fine, the VU meters move properly, all that looks good. Just nothing from Playback of a tape.

I made sure that the cables from the PB head goes to the proper header on the pcb, as well as the erase and rec heads. I’m including a picture of the wiring, it all looks good. I don’t see any blow components, and the fuses I can see are not blown.

I got the service manual from a couple of sources, but all are unfortunately a bit low rez on the board drawings, so I’m not sure just where to start troubleshooting.

ALSO: If I switch to record from the source, I get no sound when monitoring, BUT it DOES actually record quite well to tape (I move the tape to another unit to test and it was really good). When I choose TAPE MONITOR as it records, only the right meter moves (again, with no sound at the time) but it is recording to both channels.

I’m going to hook the scope up to the wires right at the back of the PB head, but that’s kinda delicate so I thought I’d seek other opinions here.

Thanks for any suggestions!


View attachment 2629187 View attachment 2629188 View attachment 2629189 View attachment 2629190

The track select switch under the head cover is notorious for killing sound in these -- make certain it's really been cleaned well. These also suffer from faulty transistors that will give you garbled/no sound in record or play or both; it's a known problem with Akai and manifests itself in almost of their decks eventually.

 

[O. Friend]

Thanks for the tips, everyone! I just cleaned that track selector switch and I'm going to replace all of those transistors tomorrow. Hopefully that'll get this thing putting out sound - it's in took good of shape to become a parts machine, haha.

 

[dr*audio]

Thanks for the tips, everyone! I just cleaned that track selector switch and I'm going to replace all of those transistors tomorrow. Hopefully that'll get this thing putting out sound - it's in took good of shape to become a parts machine, haha.

Note that the original transistors have a basing of BCE and new ones are ECB. Replace with KSC1845.

 

[O. Friend]

Note that the original transistors have a basing of BCE and new ones are ECB. Replace with KSC1845.

I'm replacing them now - testing the old 458's on my transistor tester says they are ECB - the base on the right looking at the flat side. The silk screen on the board doesn't note orientation with an icon, but one pin is noted with a solid white square - I'm assuming that is meant to signify base, since that's the way these old ones have been oriented. My replacement KSC1845's are ECB, so that makes it easy!

 

[dr*audio]

I'm replacing them now - testing the old 458's on my transistor tester says they are ECB - the base on the right looking at the flat side. The silk screen on the board doesn't note orientation with an icon, but one pin is noted with a solid white square - I'm assuming that is meant to signify base, since that's the way these old ones have been oriented. My replacement KSC1845's are ECB, so that makes it easy!

As I recall the 458 is BCE if you are looking at the side with the writing on it and the pins facing down.

 

[O. Friend]

Ok, got all 14 of the 458's replaced. With it disassembled, I played a tape and it worked! Audio solid from the RCA outs, on the meter as well. Tested recording at both speeds (capstan sleeve) and tape type setups. Was able to listen to source then switch to tape and it worked exactly like it was supposed to. Seemed great.
Then I reassembled the unit (not the case parts, just the frame etc).
Now PB won't work again.
Sigh.

I looked all over for pinched wires or unplugged cables, nothing. I hooked a scope up to the output while feeding a 1K 1v signal into the inputs, that feeds through the system just fine when selecting LINE to monitor, but playing a tape outputs nothing. I tried the scope leads on the back of the playback head - saw some random signals, so I guess they are working, but something else is stopping the signal.

 

[dr*audio]

You'll have to go through it with the scope and see where the signal is being lost. After the first amplifier the signal will be easy to see. If you have a signal generator you can connect it to the playback head. If not you can just clip a clip lead on there so it will pick up hum.
The fact that both channels are out points to either the power supply or maybe a switch linkage that is not connected. There is probably a record / play switch, maybe on the board.
Start with the power supply to the playback board.

 

[O. Friend]

Found it!
This small leaf switch (pic #1) was not being pushed out of the way enough by that slider (linked to play lever) to break contact, and when the two leaves are making contact, all sound is shut off.
I say that back further on that linkage, this silver cog (pic #2) was not hitting the lever it was intended to hit, so I loosened that screw on the left there, and slid the cog towards me so that it was on the same “plane” as the lever. That did the trick.


Although I’m wondering what that leaf contact is meant to silence, when now it seems it’s open even when play is stopped – and I can’t find too much info about that linkage. I would imagine the bar above the leaf switch would start (when stopped) just before the closed switch, then pull the one leaf out during play.

 

[Okke 70s]

Great! I suppose the GX version is a little different there from the models I know. But it looks like the sort of mechanics that could be involved with the auto-stop, at the tape's end. Nice fix

 

[dr*audio]

Found it!
This small leaf switch (pic #1) was not being pushed out of the way enough by that slider (linked to play lever) to break contact, and when the two leaves are making contact, all sound is shut off.
I say that back further on that linkage, this silver cog (pic #2) was not hitting the lever it was intended to hit, so I loosened that screw on the left there, and slid the cog towards me so that it was on the same “plane” as the lever. That did the trick.


Although I’m wondering what that leaf contact is meant to silence, when now it seems it’s open even when play is stopped – and I can’t find too much info about that linkage. I would imagine the bar above the leaf switch would start (when stopped) just before the closed switch, then pull the one leaf out during play.View attachment 2631258 View attachment 2631259

That could be a mute switch so you don't hear thribbleblibbledibble in fast forward and rewind.

 

[oldvinyldude]

Once again-a fault thought to be 'electronic' was actually mechanical. It's why I have success with some repairs-at least with R2R's and Cassette decks-most faults are mechanical in nature.