Akai GXC-760D rebuild

[bitomaxsp]

In summer 2020 i bought a subject. It was broken. Failed to even start playing.
I had never dealt with tape decks before that moment. I spent some time debugging it and found out that grease stuck in the counter gear, and belt was running around the gear. since gear was not moving, no pulses was going to the trigger, etc. So i did a simple test, replaced pulse gen pcb with pulses coming from external source, and it worked out.
Then i ordered some belts and eventually hid that beast in the cloak room because i had another interesting project to work on.

But now! Now I m reviving it again. This will be a long thread.

Pictured are from Sep 2020





And this is how it looks now, after i spent a week trying to dissassemble it completely.




I cleaned and reassembled the motors. Changed grease. And brush springs, they were dead.
Next i'll order new rollers, caps/transistors.
Test power supply.
And i'll need new measurement cassettes. If you know a good source where I can buy one, please let me know.

 

[Okke 70s]

An absolutely astonishing deck!

I completely refurbished mine a few years ago. That was a lot of work. But I did not take it apart as far as you appear to be doing.

You are aware of the must-be-replaced lownoise transistors in there?

I got a list for all replacement elco's, transistors, bulbs and whatever else if you care for it.

I'm looking forward to read about your progress on this beauty!

 

[bitomaxsp]

An absolutely astonishing deck!

I completely refurbished mine a few years ago. That was a lot of work. But I did not take it apart as far as you appear to be doing.

You are aware of the must-be-replaced lownoise transistors in there?

I got a list for all replacement elco's, transistors, bulbs and whatever else if you care for it.

I'm looking forward to read about your progress on this beauty!

Hi Okke. No i am not aware about "must-be-replaced lownoise transistors in there". Do you mind sharing any info about it? that would help a lot.
Also if you have a list and could share, I really appreciate it.

 

[Okke 70s]

It's the 2sc458 transistors you want to replace for sure.

So here is the list I found. Not as fancy as I had hoped, but might still be helpful. Original component on the left, replacement on the right. Belt, pinch-rollers and such not included




Akai GXC-760D

Power supply PCB:

2200uf 50v 2200uf 50v
1000uf 25v x2 1000uf 25v
220uf 35v x2 220uf 35v
470uf 6,3V 470uf 16v
100uf 25v 100uf 50v
10uf 25v 10uf 25v
33fu 25v 35uf 35v
outside PCB: 330uf 160V 330uf 200V

zeners WZ-240 x2 BZX79C24

transistors x2 2sc1175 BC547



Syscon

100uf 25v x3 220uf 35v
4,7uf 160v 10uf 160v
33uf 25v x5 47uf 35v
22uf 25v 22uf 50v
22uf 16v 33uf 35v
10uf 16v 10uf 25v
47uf 16v 47uf 16v
4,7uf 25v 10uf 25v
1uf 50v x8 1uf 50v MKS


motor control

varistor 3k8?/8k, 10k 10 x 5 mm
3,5 Kohm --> mouser: 652-3296W-1-332LF

pot 3,3 kohm

25v 220uf 220uf 35v
50v 0,47uf 0,68 100v MKS
50v 1uf 1uf 63v MKS
16v 10uf 10uf 25v
10v 47uf 47uf 16v
100v 1uf 1,5uf 100v MKS

motorcapacitor 6uf 150WV 6uf 450v


pre-amp

0,33 25 x2 (solid SP) 0,33uf 50v MKS
1uf 25v x4 1uf 50v MKS
4,7uf 25v (sp?) 4x 4,7uf 35v
10uf 10v (SP) x2 22uf 35v KA
10uf 16v x6 22uf 35v KA
10uf 16v x6 x2 ??? 22uf 50v fm
10uf 16v (SP zeker!) x2 22uf 16v KA
10uf 25v x14
0v fm
47uf 10v x6 47uf 25v fm
47uf 16v x2 47uf 25v fm
47uf 25v x6 47uf 25v fm
100uf 10v x6 100uf 25v fm
220uf 25v x2 220uf 25v fm

2sc1222 x4 KSC1845
2sk68a x2 2sk68a
2sc458lg x2 KSC1845

solid alu
0,15uf 25v x2 0,15uf 50v MKS
0,1uf 25v x16 0,1uf 50v MKS
0,33 25v x4 0,33uf 50v MKS

lampjes cass 8v 0,2a


VU meter

2,2uf (50v) x2 2,2 63v MKS
0,47uf (50v) x2 0,47uf 100v MKS
10uf 16v x4 10uf 25v
10uf 25v x4 10uf 25v
0,47uf 25v (solid) x2 0,47uf 63v MKS
0,1uf 25v (solid) x2 0,1uf 63v MKS
4,7uf 25v x2 4,7uf 35v (tantaal)

noise filter

0,47uf 50v x4 0,47uf 50v MKS

relay

47uf 25v 47uf 35v

overig

lamp contr. 30ma 24v 5x20mm PCB x5 30ma 24v 5x20mm
lamp schale 8v 200ma 3x15mm(?) x4 <--- 5-8v 100ma

 

[bitomaxsp]

Thanks Okke, I will use your list as a good reference.

Today i washed baseplates and reassembled it.

Very dirty, even found a spider and a web.



All screws are marked in Red so that i know i tightned them.


Also i reassembled and tuned front panel and cassette holder mechanism.
It had a scratchy feeling when i open it. I figure it is dure to the guide was stamped on the factory.



Surface was very rough, so i polished it and made it as flat as possible.


Put some grease afterwards, and now it works like a charm.

 

[Wally C]

It's the 2sc458 transistors you want to replace for sure.

So here is the list I found. Not as fancy as I had hoped, but might still be helpful. Original component on the left, replacement on the right. Belt, pinch-rollers and such not included




Akai GXC-760D

Power supply PCB:

2200uf 50v 2200uf 50v
1000uf 25v x2 1000uf 25v
220uf 35v x2 220uf 35v
470uf 6,3V 470uf 16v
100uf 25v 100uf 50v
10uf 25v 10uf 25v
33fu 25v 35uf 35v
outside PCB: 330uf 160V 330uf 200V

zeners WZ-240 x2 BZX79C24

transistors x2 2sc1175 BC547



Syscon

100uf 25v x3 220uf 35v
4,7uf 160v 10uf 160v
33uf 25v x5 47uf 35v
22uf 25v 22uf 50v
22uf 16v 33uf 35v
10uf 16v 10uf 25v
47uf 16v 47uf 16v
4,7uf 25v 10uf 25v
1uf 50v x8 1uf 50v MKS


motor control

varistor 3k8?/8k, 10k 10 x 5 mm
3,5 Kohm --> mouser: 652-3296W-1-332LF

pot 3,3 kohm

25v 220uf 220uf 35v
50v 0,47uf 0,68 100v MKS
50v 1uf 1uf 63v MKS
16v 10uf 10uf 25v
10v 47uf 47uf 16v
100v 1uf 1,5uf 100v MKS

motorcapacitor 6uf 150WV 6uf 450v


pre-amp

0,33 25 x2 (solid SP) 0,33uf 50v MKS
1uf 25v x4 1uf 50v MKS
4,7uf 25v (sp?) 4x 4,7uf 35v
10uf 10v (SP) x2 22uf 35v KA
10uf 16v x6 22uf 35v KA
10uf 16v x6 x2 ??? 22uf 50v fm
10uf 16v (SP zeker!) x2 22uf 16v KA
10uf 25v x14
0v fm
47uf 10v x6 47uf 25v fm
47uf 16v x2 47uf 25v fm
47uf 25v x6 47uf 25v fm
100uf 10v x6 100uf 25v fm
220uf 25v x2 220uf 25v fm

2sc1222 x4 KSC1845
2sk68a x2 2sk68a
2sc458lg x2 KSC1845

solid alu
0,15uf 25v x2 0,15uf 50v MKS
0,1uf 25v x16 0,1uf 50v MKS
0,33 25v x4 0,33uf 50v MKS

lampjes cass 8v 0,2a


VU meter

2,2uf (50v) x2 2,2 63v MKS
0,47uf (50v) x2 0,47uf 100v MKS
10uf 16v x4 10uf 25v
10uf 25v x4 10uf 25v
0,47uf 25v (solid) x2 0,47uf 63v MKS
0,1uf 25v (solid) x2 0,1uf 63v MKS
4,7uf 25v x2 4,7uf 35v (tantaal)

noise filter

0,47uf 50v x4 0,47uf 50v MKS

relay

47uf 25v 47uf 35v

overig

lamp contr. 30ma 24v 5x20mm PCB x5 30ma 24v 5x20mm
lamp schale 8v 200ma 3x15mm(?) x4 <--- 5-8v 100ma

I'm also planning to re-cap and change "funky" transistors in my GXC-760D. So I'm wondering is there any particular reason to replace solid aluminum caps with MKS caps? How about 2SK68A MOSFET? I haven't heard any particular bad stories about this one (unlike 2SC458). I know this is not a big deal to replace it, but I already have all bipolar replacements on hand but not MOSFET.

Thanks...

 

[Okke 70s]

Great, they are worth it!

The solid aluminium caps (light bleu sanyo's) are also famous for going bad over time. They develop high internal resistance, if I'm not mistaken. I replace them usually with Wima MKSII. They where supposed to be very stable, at the time, so usually they sit at places where stability is important.

As for the 2SK68A I don't recall specifically. It might be that they looked or tested bad, or that I could get them easily and decided to just finish the transistor replacement job.

I do seem to remember that the 22uf (Nichicon) KA caps replacing the 10uf couplers right at the head didn't do great. I think I put 10uf high quality mylar caps in later, and that really was an improvement.

 

[Wally C]

Great, they are worth it!

The solid aluminium caps (light bleu sanyo's) are also famous for going bad over time. They develop high internal resistance, if I'm not mistaken. I replace them usually with Wima MKSII. They where supposed to be very stable, at the time, so usually they sit at places where stability is important.

As for the 2SK68A I don't recall specifically. It might be that they looked or tested bad, or that I could get them easily and decided to just finish the transistor replacement job.

I do seem to remember that the 22uf (Nichicon) KA caps replacing the 10uf couplers right at the head didn't do great. I think I put 10uf high quality mylar caps in later, and that really was an improvement.

Thanks for a quick response. I really appreciate. Everything you've said makes perfect sense. Thanks again.....