Akai GX-635D Repair - Won't Do Tape Recording

This is a repair video for Akai GX-635D which won't do the tape recording. This is a common issue for this unit. So I hope this video will help other GX-635D users who have the same problem. We always blame the aged I/O coupling capacitors for causing the signal path failure. However, I found the problem may be also caused by the defective transistors in the preamp section. Please leave your comments and suggestions if you have any experiences with this unit. Thanks for watching.

[@ericblondeau184]

Thank you very much sir for this video...tonight i repaired my great AKAI GX-635D and it sound great and he records like new one..Thank's to you !!!!!

[@VintageAudioFan]

I am glad this video helps. By posting the videos on this channel, I can also share my own experiences because I have benefited greatly from other's sharing before.

[@markchapman7326]

Hi ! I'm not technician but found 20 transistors 2SC458 Hitachi (knew as problematics) in my unit. Unit do not recording both way. My question is if I do replace these 20 transistors 2SC458 , will my unit recording both way again ?

[@dannyyy1012]

Have a GX-635D recently but it does not play, it powers up, but no green light comes on, nor any function works like rewind or record. Not sure what that would be. There is tape mounted on it. But no movement of the capstan or motor sound

[@VintageAudioFan]

From your descriptions, it seems that your GX-635D may have a defective power supply problem. I suggest to check the FUSE PC board TH-2040. There are four fuses on it. The followings are their power supply functions: (1) Fuse #2 - capstan motor (2) Fuse #3 - reel motors (3) Fuse #4 - record/play amplifiers (4) Fuse #5 - logic control board which handle play/stop/forward/reverse switch functions. If all fuses are good, then you may have defective components in the power supply board which requires further diagnose and repair.

[@dannyyy1012]

@@VintageAudioFan Thank you for your answer, I'll look into that as it is a good indicator and starting point to see if the problem is visible there. But a blown fuse is always an idicator of something failing thus in need of a check I've noticed that these are prone to transistor failure as well. Maybe that is what's the issue but until then I will tackle that first. Replacement shouldn't be a problem but maybe the lack of a scope or is it possible to work on it without a scope

[@rotterdamaudiocreator]

Hello Sir! I have the same deck, maybe you can lead me the way… rewind is very very slow and sometimes it stops? And second.. the vu-lights are not bright but very low? Greetings Tony (holland europe)

[@VintageAudioFan]

It seems there is a problem in the power supply which caused it doesn't have enough voltage supply to motor and VU meter lamps.

[@vfdffdd2675]

Bravo and tnx for subtitle.

[@animalcorvair]

great vid i just started using my 635d ,,,plays fine but went to record both chan have no meter working an i made a check to see if i am hooked up right on my sta 2000 rec an i am,,, bet it has bad 458 trans on both sides i did fix the right playback side with new tran in 2007 ,,looks like i should replace all ,,,

[@animalcorvair]

just to let you know my boy changed out 14 458 trans....it recording an playing great now....i showed him the ones i changed on playback in 2007 ...

[@toninosegreto2]

Thanks for this video... i repaired my AKAI GX-635D it recorder only one left channel. Now it's records on Left and Right ch with great sound ....... I also recorder trimmer VU meter... Thanks again to you !!!!!

[@camng6909]

Thanks for sharing your knowledge. It’s a great clip for repairing. I have the same problem with left channel won’t record. I don’t have a schematic. Can you ping point the location of tr3 and tr4 on the preamp board? Thanks in advance.

[@VintageAudioFan]

Please send your inquiry via email. The email address is shown under "About" in my KZbin home page.

[@ignacioromero5014]

Thank you! I have a logical direction to start now. God bless

[@istvankocsis5507]

I had similar problem recently in playback the right side disappeared and find that the problem is with the t7 2SC458 transistor wich hfe dropped to 34! Otherwise in diode mode the tests was ok but the DC parameters differed. After some research I found an article with the titel Defective Hitachi Brand Transistors on reeltoreeltech wich is about the corrosion problem of 2SC458 transistors: 'The theory is that the wire leads of the Hitachi transistor get corroded over time, and that corrosion slowly creeps into the To-92 package, where it corrodes the silicone substrate of the transistor. This can lead to intermittent audio, distorted audio, or high background noise levels. On occasion, an audio channel can go completely dead, but left off overnight, the channel can start working again the next day. Even more annoying, if you pull the transistors out of the tape deck, they test just fine in a transistor tester. If you put a voltmeter on the transistor, then the readings are a mile off from what they should be, so our theory is that the transistor junction breaks down when an operating voltage is applied to it, but under the lower voltage of a transistor tester, they check OK.'

[@VintageAudioFan]

Thank you for your sharing. I agreed what you said about some faulty transistors can't be detected. Because they show completely fine on the tester. I have a upcoming video which will show the similar issue caused the non output in the preamplifier section.

[@istvankocsis5507]

​@@VintageAudioFan I searched for the best replacement as all similar transistor is a potential failure source and find the 2SC or KSC 1815 wich has identical parameters but lower noise figure typ 1.0 dB.

[@10zic]

Hello. I recently bought a broken Akai 635d. The left channel in the reverse did not work, I replaced all the transistor 458 and everything is ok with playback. The problem is with the recording, when I want to record the signal appears on the input, both indicators work, but pressing the tape there is silence. The previous recording is replaced with silence. So the recording mode works. Where could be the problem. Where in the diagram is the rec mute system, maybe it causes the problem. Please help.

[@VintageAudioFan]

To answer your question, can you send your inquires to my email?

[@VintageAudioFan]

I tried answering your questions but it won't send to you. Could you use other valid email address so I can provide you the solution?

[@VintageAudioFan]

This is the email I sent to you: "From your description, I marked up a signal path on the attached circuit diagram, there are some parts that may cause the problems. So I came up with some assumptions: 1. Transistors TR7/TR8 non function - either defective or no correct voltage (1.4V/6.3V) on collectors. 2. Capacitors C22/C31 are defective. 3. Monitor/Tape switch is defective 4. Check all components inside the marked green square area. In most cases when both channels don't work at the same time, it usually indicates that the problem is in the power supply. So Please check the #1 on my list first and let me know if it is the case.I will help you with the motor speed issue after figuring out the recording problem."

[@tomaszczyzyk6148]

Great video,much appreciated 👏👏👏

[@VintageAudioFan]

Glad you enjoyed it

[@midmodaudio6576]

excellent video, thank you !

[@SDsailor7]

Excellent troubleshooting!

[@zipnemesis]

Thank you.

[@VintageAudioFan]

You're welcome!

[@skullheadwater9839]

I just bought this tape recorder for cheap because broken. No fast forward, No rewind, No play in either direction, capstan does not move up to push tape to head, no green led above play buttons. Amplifier and heads work because if I rotate reels manually I hear recording on the tape. The main motor in the center is spinning when turned on. Where to start? Any advice?

[@VintageAudioFan]

Based on your descriptions, the issue may be caused by the defective (1) power supply or (2) operation control PCB. I suggest you to check the fuse PCB (TH-2040) at top right corner at back side of unit. There are 4 fuses on PCB includes: F2 (1.6A) & F3 (800mA) both for reel motors operation (Play, Rev and Brake) ; F4 (800mA) for preamp PCB and F5 (for operation/control circuit and meter lamps). Please let me know the result and send me information via email.

[@thanhnguyen-xi8fq]

This video should name: Akai 635D NO LEFT CHANNEL Output from RCA IN...because with this faul, if you tried to listen to music from RCA input, left channel will be missing, not even when you tried to record anything... No Recording problem is a total different fault on this machine.

[@VintageAudioFan]

Thank you for the comments. I think the title could be "Akai GX-635D Preamp Repair" and it covers the no-recording issue.

[@Cuongtomato]

Could you please tell me where did you buy that transistor ? Thank you so much

[@VintageAudioFan]

The transistor 2SC458 (made by NEC & Hitachi) was designed for low noise audio amplifier use in the 1970's. It can be replaced by the newer generation transistor KSC1845 which can be purchased at Mouser, Digi-Key....etc. Also there are some vendors selling 2SC458 in the eBay, but I can't verify them if they are the true OEM products.

[@SDsailor7]

Do the VU meters have to move equally at all times when the music is playing? Or does the meters move according to the sound level of the music in each channel? Does anyone know? Thank you

[@VintageAudioFan]

The VU meters move according the track sound level which tape is recorded. So they don't move equally. There is a an adjustment in the deck which you can adjust both channel VU meter to the same level when the input signals are at same strength.

[@SDsailor7]

@@VintageAudioFan Thank you i always wondered about that.

[@williamchow1624]

WOW! It works.