Akai GXC-730D - UK Vintage Radio Repair and Restoration Discussion Forum

Mitch-W · 28th Feb 2016, 5:04 am

Hi!
I got this nice tape deck from my uncle. He played it last time in the mid 90s.
I plugged it in, and it worked, but the Pause swtich was on. I lubed the mechanism for the switch, and then it worked.
Works a treat, the controls are very good, also the sound is very good.

But, I have a problem. The left channel VU meter is dead. The meter itself is good and will move if I test it using ohm meter. However, I don't get anything on the output lead for the meter.

I looked at the schematic (link) and found most probable culprit TR6 transistor. I measured it and it looked leaky, also the E-C and B-C junctions both read 0.7V in diode check. I swapped with the TR5 and the left channel went silent. I changed it then for BC337, but it didn't work. Capacitors look fine, when I tested some with an ESR meter.

Should I first get the proper 2SC945 transistor, or do I perhaps have a problem somewhere else?

Restoration73 · 28th Feb 2016, 2:55 pm

Note the BC337 uses a different pinout (EBC) the 945 is BCE. If you replace the
transistor and get a signal both channels using the headphone jack, then it might
be the diode. Nearest euro device with same pinout is BC182L (or BC184L).

Mitch-W · 28th Feb 2016, 5:19 pm

Thanks for the reply.
I get both the left and right channels, so I believe that the only thing I am missing is a VU meter drive.

Of course I noticed that the pinouts are different, so I swapped the pins of the BC337. But perhaps the specs are also too much different from the 2SC945...

paulsherwin · 28th Feb 2016, 5:55 pm

The 2SC945 is just a Japanese jellybean transistor like a BC548 or 2N3904. Your BC337 should have worked if you wired it correctly. If you're certain you did, then the fault is elsewhere.

There's no point in trying to source an actual 2SC945.

Mitch-W · 2nd Mar 2016, 11:32 pm

I put in the 2SC1815 and now the both VU meters rock

Any suggestions of calibrating the VU meters? What is the proper method?
I used the android mobile phone with an Audio Generator app and connected it to inputs. Selected the 333 Hz frequency sine wave. I put both recording levels to the max and lowered the volume on the phone so the needles were somewhere in the middle.
Then I adjusted the pot for the left channel (the one I replaced the transistor), so it matched the right channel.

The only problem is if I put that much signal that the needles would go almost all the way in the red, then the left channel is a bit lower than the right at the same input.

28th Feb 2016, 5:04 am	#1
Mitch-W Tetrode Join Date: Feb 2015 Location: Celje, Slovenia Posts: 70	Akai GXC-730D Hi! I got this nice tape deck from my uncle. He played it last time in the mid 90s. I plugged it in, and it worked, but the Pause swtich was on. I lubed the mechanism for the switch, and then it worked. Works a treat, the controls are very good, also the sound is very good. But, I have a problem. The left channel VU meter is dead. The meter itself is good and will move if I test it using ohm meter. However, I don't get anything on the output lead for the meter. I looked at the schematic (link) and found most probable culprit TR6 transistor. I measured it and it looked leaky, also the E-C and B-C junctions both read 0.7V in diode check. I swapped with the TR5 and the left channel went silent. I changed it then for BC337, but it didn't work. Capacitors look fine, when I tested some with an ESR meter. Should I first get the proper 2SC945 transistor, or do I perhaps have a problem somewhere else?

28th Feb 2016, 2:55 pm	#2
Restoration73 Nonode Join Date: Jun 2013 Location: Surbiton, SW London, UK. Posts: 2,801	Re: Akai gxc-730d Note the BC337 uses a different pinout (EBC) the 945 is BCE. If you replace the transistor and get a signal both channels using the headphone jack, then it might be the diode. Nearest euro device with same pinout is BC182L (or BC184L).

28th Feb 2016, 5:19 pm	#3
Mitch-W Tetrode Join Date: Feb 2015 Location: Celje, Slovenia Posts: 70	Re: Akai GXC-730D Thanks for the reply. I get both the left and right channels, so I believe that the only thing I am missing is a VU meter drive. Of course I noticed that the pinouts are different, so I swapped the pins of the BC337. But perhaps the specs are also too much different from the 2SC945...

28th Feb 2016, 5:55 pm	#4
paulsherwin Moderator Join Date: Jun 2003 Location: Oxford, UK Posts: 27,966	Re: Akai GXC-730D The 2SC945 is just a Japanese jellybean transistor like a BC548 or 2N3904. Your BC337 should have worked if you wired it correctly. If you're certain you did, then the fault is elsewhere. There's no point in trying to source an actual 2SC945.

2nd Mar 2016, 11:32 pm	#5
Mitch-W Tetrode Join Date: Feb 2015 Location: Celje, Slovenia Posts: 70	Re: Akai GXC-730D I put in the 2SC1815 and now the both VU meters rock Any suggestions of calibrating the VU meters? What is the proper method? I used the android mobile phone with an Audio Generator app and connected it to inputs. Selected the 333 Hz frequency sine wave. I put both recording levels to the max and lowered the volume on the phone so the needles were somewhere in the middle. Then I adjusted the pot for the left channel (the one I replaced the transistor), so it matched the right channel. The only problem is if I put that much signal that the needles would go almost all the way in the red, then the left channel is a bit lower than the right at the same input.