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Vintage Tape (Audio), Cassette, Wire and Magnetic Disc Recorders and Players Open-reel tape recorders, cassette recorders, 8-track players etc.

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Old 14th Feb 2018, 12:59 am   #1
hsbhachu3d
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Default Akai gx365

I got this deck but it has a peculiar problem and I do not know where to start.

It is a 4 track Auto reverse deck and also has inbuilt amplifiers. It is a 3 head deck and the Play head is moved into a lower position when playing in reverse.

It plays/ records fine. but when you press the reverse the reverse button, it plays in reverse but much faintly from the right channel.

It is obviously not the head because the head picks up 2 tracks and plays fine in forward and not in reverse.

the tape is also fault free, flipped it over, same problem.

Relay bad? Capacitor bad? Switch bad? in the reverse circuit?
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Old 14th Feb 2018, 2:22 am   #2
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Default Re: Akai gx365

If the switching is done by those long slide switches, clean and lubricate them - they always seem to play up. I uses CRC CO then CRC 2.26, but those are probably not available in the UK so others can advise similar products.
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Old 14th Feb 2018, 4:38 am   #3
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Default Re: Akai gx365

Got the culprit. A relay that does not close properly . took it apart and cleaned the contacts with a fine strip of super fine sand paper. done the trick.

BUT also found a new issue. the machine records but the recording is faint. both channels. VU's adjusted properly and source shows alright but when monitoring tape the recording is literally dead. It's like the transistors or something are throwing a fit.
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Old 14th Feb 2018, 5:24 am   #4
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Default Re: Akai gx365

arjoll has it in one!!!

I was service manager for Akai Australia for a couple of years. Those slide switches are the culprit. I actually resigned over that exact problem.

Joe
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Old 14th Feb 2018, 5:58 am   #5
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Default Re: Akai gx365

Quote:
Originally Posted by hsbhachu3d View Post
BUT also found a new issue. the machine records but the recording is faint. both channels. VU's adjusted properly and source shows alright but when monitoring tape the recording is literally dead. It's like the transistors or something are throwing a fit.
Are you seeing bias on the record heads?
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Old 14th Feb 2018, 12:33 pm   #6
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Default Re: Akai gx365

Seeing bias? if the bias circuit is working? I can assume it is, because I attempted to make a recording with the bias board removed and all I got was faint crackles.

Put the bias board back and it started recording the same low again but I it's something like, If I set the source levels to 0DB, the recording will be something like -6 db on the VUs. Ironically equal on both channels. Increasing the level gets the recording up to nearly 0 db but it starts to clip and I'm way high up on the source input

Last edited by hsbhachu3d; 14th Feb 2018 at 12:47 pm.
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Old 14th Feb 2018, 6:02 pm   #7
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Default Re: Akai gx365

I demagged the head and the recording although low is rather clear and very good actually. Just need to figure out why it is so low
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Old 14th Feb 2018, 7:38 pm   #8
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Default Re: Akai gx365

Right, There is the rec amp schematic. I have read on many forums online that the 2SC968 transistors are prone to die or get noisy with age.

Any suggestions on what I can substitute or if these are viable culprits?
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Old 15th Feb 2018, 3:46 pm   #9
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Default Re: Akai gx365

BC549 probably will substitute OK (that's a lower-noise version of a BC547). It has a higher turnover frequency and a lower maximum collector voltage, but still within ratings in this circuit. Package is TO-92 with base in the middle, so should fit a board already laid out for TO-18.
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Old 15th Feb 2018, 8:22 pm   #10
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Default Re: Akai gx365

So far, I've Recapped most of the Play boards and record boards, there are about 2 caps that I've left as I don't have replacements, but It records now. However, it clips on the low end.. say if you record a sine wave between 25-100 hz, it'll sound as though I've maxed it out, anything above that until 18k is good.
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Old 22nd Feb 2018, 11:20 am   #11
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Default Re: Akai gx365

All new transistors on play board.. Playback is perfect, recording board also all new 2sc 458s , I've left the 454s and 968 on there. Put a new original matched Rec Head. calibrated the whole deck and sounds nearly perfect at 7.5 ips. 3.75 sounds worse than my 4000DS mk1. what shall I do? I think something is up and maybe the record head is not getting the max its meant to get .

was thinking of replacing the 968
2n 2222 is the best equivalent replacement for the 2sc968 which is the record output transie but just worried not to screw anything up.


What shall I do? dead end.
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Old 23rd Feb 2018, 5:47 am   #12
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Default Re: Akai gx365

Quote:
Originally Posted by hsbhachu3d View Post
So far, I've Recapped most of the Play boards and record boards, there are about 2 caps that I've left as I don't have replacements, but It records now. However, it clips on the low end.. say if you record a sine wave between 25-100 hz, it'll sound as though I've maxed it out, anything above that until 18k is good.
Normally we check record/playback response at levels 20db below 0 on the machine's VU meter but especially at the slower speeds.

Also I think the old Akai would be designed around NAB curves which from memory used to boost the deep bass on record and cut it by the same amount on playback. Another reason to make these frequency response tests at low levels to avoid overloading.
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Old 23rd Feb 2018, 11:52 pm   #13
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Default Re: Akai gx365

Right,

I got somewhere. Replaced the 2SC454s on the record board as well, so all caps on the REC board and all transistors apart from the Rec output ones are new. All legit Hitachi ones.

The recording at 7 and a half is stunning. Bass response is good on all 3 speeds. however one last thing to make this deck 100% is the high end at 3.75 dies off MUCH earlier than my 4000D. You can tell from the stressed 'S' ess sound where it is not there on any of my other 4 decks recording at 3.75. It plays other tapes recorded at 3.75 perfectly without the stressed high end. Or do GX heads just have a worse signal ratio compared to perma alloy heads at lower speeds?
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Old 25th Feb 2018, 9:40 pm   #14
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Default Re: Akai gx365

Are there separate bias controls for each speed? Could it be over biased at 3.75?
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Old 26th Feb 2018, 3:59 am   #15
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Default Re: Akai gx365

Quote:
Originally Posted by hsbhachu3d View Post
The recording at 7 and a half is stunning. Bass response is good on all 3 speeds. however one last thing to make this deck 100% is the high end at 3.75 dies off MUCH earlier than my 4000D. You can tell from the stressed 'S' ess sound where it is not there on any of my other 4 decks recording at 3.75. It plays other tapes recorded at 3.75 perfectly without the stressed high end. Or do GX heads just have a worse signal ratio compared to perma alloy heads at lower speeds?
Hard to be sure. It might depend on the condition of the GX heads. Ferrite heads were designed for very long life but could have a problem called "crystal pullout" where tiny pieces of ferrite at the edges of the head gap fell out, messing up the clean, narrow head gap. Look at the heads under a strong magnifier in a good light, especially the gap areas.

Of course it also depends on the tape type used. Older tapes will struggle with the highs especially at the slower 3.75ips. The slower the tape speed, the more everything has to be carefully optimised. The treble is the first thing to go.

Best take it methodically one step at a time, referencing the machine's playback response to your other machines - or preferably via a calibration tape. I tested a GX machine I have with a fresh calibration tape and its playback response drooped in the highs, whereas my Revox machines' playback responses were very close to the standard. Ferrite type heads can be a mixed blessing.

As James says it could be the bias. The machine could be overbiased for the tape you are using.
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Old 28th Mar 2018, 1:02 pm   #16
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Default Re: Akai gx365

Sorted. It was the record head. I ordered another 3, costed about 100 quid each from different parts of the world Lol

One was good out of the lot.

Sorted the bias and it was fine.
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Old 28th Mar 2018, 2:26 pm   #17
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Default Re: Akai gx365

Well done! What was wrong with the original, do you thinK?
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Old 29th Mar 2018, 9:57 pm   #18
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Default Re: Akai gx365

Quote:
What was wrong with the original, do you thinK?
Gap wear causing the tape to head contact to be had on the right channel. To be honest, The GX heads are not really all that good compared to the 'one Micron gap' Alloy heads. The Ferrite wears faster than the glass. Issue is, the ferrite is what records the signal. The head does not wear evenly. The idea that GX heads don't wear is false. Timtape's advice came handy.

Quote:
Originally Posted by TIMTAPE View Post
Hard to be sure. It might depend on the condition of the GX heads. Ferrite heads were designed for very long life but could have a problem called "crystal pullout" where tiny pieces of ferrite at the edges of the head gap fell out, messing up the clean, narrow head gap. Look at the heads under a strong magnifier in a good light, especially the gap areas.

Last edited by hsbhachu3d; 29th Mar 2018 at 10:17 pm.
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