Adopted beautiful old Casio 401 - turns on, hum, but no sound.

[freakyooota]

No identifiable blown capacitors or burned PCB.

 

There is a little sound, especially in the higher octaces - but its faint - and i mean its really  faint.

 

- Jack tested.

- Fuses all good (replaced one).

- Key-ribbon looks good.

- Correct voltage set

 

I will attach pictures maybe it can help.

 

Thank you folks.

 

https://postimg.cc/gallery/8FRTSBC

Edited June 8, 2024 by freakyooota
photos didnt upload

[Chas]

6 hours ago, freakyooota said:

No identifiable blown capacitors or burned PCB.

 

There is a little sound, especially in the higher octaces - but its faint - and i mean its really  faint.

 

- Jack tested.

- Fuses all good (replaced one).

- Key-ribbon looks good.

- Correct voltage set

 

I will attach pictures maybe it can help.

 

Thank you folks.

 

https://postimg.cc/gallery/8FRTSBC

 

 

Congratulations on acquiring a vintage Casiotone! Those are lovely old keyboards with warm tones and analogue percussion, and are well worth having and using. Also of interest is that it is one of the models that includes the now famous "Frog" preset famously used on Michael Jackson's "Thriller" song!

With regards to yours and its issues, looking at your pictures the first things that come to mind are the following:

In the picture below I've arrowed a small rectangular yellow capacitor, known as a RIFA film capacitor. These are notorious for going kamikaze by popping and producing a lot of smoke when they do, though yours looks fine. My understanding is that they are used as a noise suppressor in the PSU circuit. They can be cheaply and easily replaced with modern equivalents.

I've also arrowed two missing fuses. Have both these been replaced, and why were they missing in the first place?

 

 

 

Another possible culprit is the Power Amplifier module arrowed in the picture below. Could also be an issue with circuitry and components around it:

 

 

 

Lastly, have you checked both the headphone out and line outs to see if they both suffer from very faint volume? When you switch the keyboard on, can you hear a small 'pop' sound from the speaker?

Can you start and hear the rhythm section playing when activated (even faintly)? Do the LED lights respond when you press switches on the front panel?

Starting with the basics, try wiggling the volume control back and forth, and try it at various positions to see if an oxidized/ dirty potentiometer might be the issue. Also try the doing the same thing with the balance control. Quite often volume issues are caused by volume potentiometers not working correctly.

If all the above doesn't produce any results, it's time to use a Service Manual and dive in deeper. I managed to find one online and will upload it into the files section of the forum.

Good luck, and I hope you manage to get your 401 singing again 🙂
 

Edited June 8, 2024 by Chas

[Chas]

I uploaded the 401 Service Manual to the Downloads section of the forum. Here's a direct link:

https://www.casiomusicforums.com/index.php?/files/file/1599-casiotone-ct-401-service-manual/

Edited June 8, 2024 by Chas

[IanB]

Excellent comments from Chas above. The RIFA looks ok (they normally fail apocalyptically) and aren't required for circuit function anyway (you can just remove it if you want tbh, it's there to comply with regulations basically). It certainly won't work with missing fuses!

[CYBERYOGI =CO=Windler]

Do not permanently remove mains filter caps! Even if it won't hum too bad, it may cause longterm damage destroying irreplacable special ICs because increased hum/mains dirt (in worst case causing oscillating voltage regulator) on supply voltage lines causes additional capacitive currents those heat up chip parts not designed to handle this. (For a quick test it may be safe, but not longer.)

 

E.g. certain rare 1980th NuTone door chimes (LBC55 etc. = early IoT predecessor with clock chime, burglar alarm and all bells and whistles despite feeble monophonic squarewave melodies) tend to die of mains dirt when dying PSU caps are not replaced.

Edited August 15, 2024 by CYBERYOGI =CO=Windler