Akai GX630DB - UK Vintage Radio Repair and Restoration Discussion Forum

Nige135 · 10th Jul 2020, 8:04 pm

Hi all
I have a Akai gx630db
After pressing play it will slow down and stop after about a minute has anyone come across this problem.
I have changed the tip 47 and a few diodes but it still has the fault.
By
Thanks

DMcMahon · 10th Jul 2020, 11:33 pm

Are you happy that the tape path (heads/tape guides etc) have not got coated up with sticky tape deposits ? Can you see if the capstan shaft is still rotating when the issue occurs ?

David

Nige135 · 11th Jul 2020, 8:10 am

Yes everything is clean capstan runs no problem it is acting like it loses power when it stops you can hear relay click but nothing will engage until switched off and then back on.

DMcMahon · 12th Jul 2020, 4:56 pm

I also have a GX-630DB but luckily never had any real problems with it, so have never really had to do any technical investigations, but do remember that some of PCB circuity is less than easy to access.

Presumably the capstan stops rotating when the issue occurs, otherwise the tape would still be moved forward by the pinch roller (assuming brakes are released by the brake solenoid & the Pinch Roller solenoid operates to press the tape against the capstan shaft) even if the Take Up reel table reel motor drive does not operate.

First thing I would check is the +24 volt DC supply, this can be measured at pin 6 of the Relay PCB wrt (with respect to) ground and should be adjusted by the VR-1 potentiometer at the Relay board for 24 volts.

Also make sure this voltage stays good in the fault condition. The +24 volts is the main supply to the relays (that control Forward, Fast Forward & Rewind), to System Control board (SYS-CON) and to the Motor Servo for the Capstan motor.

If 24 volts is good, brakes releasing, pinch roller operating then really it is a case of using the schematics from the Service manual to check through the control signals and motor control which can be a hard slog, to better establish what is occurring.

David

DMcMahon · 13th Jul 2020, 10:39 pm

Quote:

Originally Posted by Nige135

I have changed the tip 47 and a few diodes but it still has the fault.

I wondered where the TIP 47 was used, I see it is on the output stage of the Servo board for the Capstan motor.

I guess the referenced diodes most likely are D2 to D5 the rectifier diode bridge on the Servo board ?

DMcMahon · 14th Jul 2020, 9:02 am

Is the Play problem the same in both tape speeds ?

BRASSBITS · 14th Jul 2020, 11:34 am

have you tried it in play mode with no tape on it

DMcMahon · 14th Jul 2020, 10:12 pm

Got my GX-630DB out and running. If any signal monitoring required for comparison then please advise.

10th Jul 2020, 8:04 pm	#1
Nige135 Diode Join Date: Jul 2020 Location: Telford, Shropshire, UK. Posts: 2	Akai GX630DB Hi all I have a Akai gx630db After pressing play it will slow down and stop after about a minute has anyone come across this problem. I have changed the tip 47 and a few diodes but it still has the fault. By Thanks

10th Jul 2020, 11:33 pm	#2
DMcMahon Dekatron Join Date: Apr 2019 Location: Worthing, West Sussex, UK. Posts: 6,600	Re: Akai gx630db Are you happy that the tape path (heads/tape guides etc) have not got coated up with sticky tape deposits ? Can you see if the capstan shaft is still rotating when the issue occurs ? David

11th Jul 2020, 8:10 am	#3
Nige135 Diode Join Date: Jul 2020 Location: Telford, Shropshire, UK. Posts: 2	Re: Akai gx630db Yes everything is clean capstan runs no problem it is acting like it loses power when it stops you can hear relay click but nothing will engage until switched off and then back on.

12th Jul 2020, 4:56 pm	#4
DMcMahon Dekatron Join Date: Apr 2019 Location: Worthing, West Sussex, UK. Posts: 6,600	Re: Akai GX630DB I also have a GX-630DB but luckily never had any real problems with it, so have never really had to do any technical investigations, but do remember that some of PCB circuity is less than easy to access. Presumably the capstan stops rotating when the issue occurs, otherwise the tape would still be moved forward by the pinch roller (assuming brakes are released by the brake solenoid & the Pinch Roller solenoid operates to press the tape against the capstan shaft) even if the Take Up reel table reel motor drive does not operate. First thing I would check is the +24 volt DC supply, this can be measured at pin 6 of the Relay PCB wrt (with respect to) ground and should be adjusted by the VR-1 potentiometer at the Relay board for 24 volts. Also make sure this voltage stays good in the fault condition. The +24 volts is the main supply to the relays (that control Forward, Fast Forward & Rewind), to System Control board (SYS-CON) and to the Motor Servo for the Capstan motor. If 24 volts is good, brakes releasing, pinch roller operating then really it is a case of using the schematics from the Service manual to check through the control signals and motor control which can be a hard slog, to better establish what is occurring. David

14th Jul 2020, 9:02 am	#6
DMcMahon Dekatron Join Date: Apr 2019 Location: Worthing, West Sussex, UK. Posts: 6,600	Re: Akai GX630DB Is the Play problem the same in both tape speeds ?

14th Jul 2020, 11:34 am	#7
BRASSBITS Hexode Join Date: Dec 2018 Location: Sheffield, South Yorkshire, UK. Posts: 364	Re: Akai GX630DB have you tried it in play mode with no tape on it

14th Jul 2020, 10:12 pm	#8
DMcMahon Dekatron Join Date: Apr 2019 Location: Worthing, West Sussex, UK. Posts: 6,600	Re: Akai GX630DB Got my GX-630DB out and running. If any signal monitoring required for comparison then please advise. Attached Thumbnails