Vox Jaguar - a missing undertone on all F's

[gimp554]

Hello,
I'm quite far in restoring my Vox Jaguar, but there are still two problems I'm not able to solve:

1. There's a missing undertone on all F's including the Bass-section (If you press a single key on the Jaguar, you can usually hear two tones, even when just one single register is selected)

2. If I press both A's - the tone is distorted by an unwanted slow and heavy vibrato, some kind of grinding tone. The more keys are pressed additional, the higher is the intensivity of this grinding tone. If i press only one A or a few other keys (without two A's), the .tone is normal as it should be without the unwanted "vibrato"

This problems are probably caused by moisture/corrosion - this was the causation of the other problems I've already solved.
Did anyone know this problems or have any idea where to locate and how to fix this.
It would be also very helpful, if somebody has a schematic or know where I can get one.

Thanks and Best Regards,
Christian

[karl]

Hi there,

If you have had moisture/corrosion problems, I would take some alcohol and a toothbrush and clean the top and especially the bottoms of all the circuit boards in there. Dry it good with a hair dryer or sim before turning it on. The problems you describe, ( unwanted vibrato ) could easily be caused by corrosion between circuit board traces.
Look closely at any areas where corrosion has occurred.
You may have to re solder some broken traces that has been eaten up by the corrosion.
Also, check out the Key contact cleaning post in the technical support page. Dirty key contacts are the cause of many combo ills.

- Karl

[gimp554]

Thanks-a-lot for your tip! But I couldn't find any corrosions on the circuit-boards for F and A. The only corrosion I found was on the screw which holds the circuit-board. The photo below shows the upper- and underside of both circuit-boards. Do you see anything suspicious?
I discovered that one can remove the cap of the transistor. Is it possible thats there is a corrosion problem inside the transistor or did my problems points into another direction (i didn't had the heart to remove the cap so far).
Thanks and Best Regards,
Christian

Attachments:

[karl]

Hi ,
No other corrosion is good.

Picture ? Am I looking in the wrong place?

Are you sure thats a transistor? If you can pull the cap off of it well thats not good, The transistor is probobly shot.

- Karl

[gimp554]

Hello Karl,

No other corrosion is good.

Yes, but the screw has no direct contact with the circuit-board, there is a thick piece of felt between

Picture ? Am I looking in the wrong place?

Can't you see the picture from my attachment? Then follow this link: combonation.proboards.com/index.cgi?action=downloadattachmentpage&board=technicalquestionsgohere&thread=500&post=1665

Are you sure thats a transistor? If you can pull the cap off of it well thats not good, The transistor is probobly shot.

No, I'm not sure, I thought it was a transistor. I mean the big thing with the metal-top, where you can tune the tone with a screwdriver.
I can't pull the cap off, but the cap is hold by two sheet-tongues, so its possible to have a look inside. I thought that there's maybe some sort of corrosion which cause my problems.

Best Regards,
Christian

[karl]

Okay I see the pics now. The large thing we are talking about is the tunning coil, or inductor. It tunes the card for
whichever note it generates. It is basically just a coil of wire.
So yes, its possible that moisture got under the cap and corroded the wire. If you have an ohmmeter you can measure across its terminals to see if its open. The resistance shoould be low > 500 ohms. But, I would definetly take a look inside.

The boards look pretty good from here. Do you have access to an oscilloscope ? Cause once you have eliminated all posible mechanical problems ( broke wire, etc...) this can be a quick way to find the problem.

Best Regards

- Karl

[gimp554]

Hello Karl,

If you have an ohmmeter you can measure across its terminals to see if its open. The resistance shoould be low > 500 ohms

Inductor is OK. I measured the Inductors from F and A across the Terminals and got the same values from both (ca. 230 Ohm).

Do you have access to an oscilloscope ? Cause once you have eliminated all posible mechanical problems ( broke wire, etc...) this can be a quick way to find the problem.

A Friend got one and I brought the organ to him. He wants to test the boards the next days. He has no experience with organs, but knows a lot about electro-technics.

There are some facts about the defect from the A i didn't noticed before:
- If I press the lowest A alone without vibrato-effect, I've got a normal tone as he should be. If I switch the vibrato on, I hear the same distortion If I press two A's (higher A's pressed alone didn't have this problem)
- "unwanted vibrato" is a bad description, one can hear some sort of slow oscillation but also some sort of cracking noise .
- I changed a working circuit-board (from the G) with the A, but nothing changed (except that the the keys A and G was interchanged)

Best Regards,
Christian