82E02 EQ card issue **SOLVED**

[oyanliz]

Hi,

I am recapping the channels of the new console we bought. After recapping the first 10 channels, we have decided to test the channels. There are things to fix, but there is an issue in all the 82E02 EQ cards. We have tested 3 channels and the EQ gets crazy in all of them when moving the HMF knob above 3KHz.
We have swapped the EQ card is all these channels, by a card removed from our working console. The eq card is the same, 82E02 and have been recapped one year ago.
I have recapped the eq cards with 8 Panasonic FR 100uF 10v capacitors and 2 Panasonic FR 10uF 50v capacitors. The cards don't work good.
The other card recapped a year ago, it has 8 capacitors with 100uF 35v (I don't know the brand) and 2 caps 10uF 63v. With this card, all the channels work fine.

I have checked  polarities of caps and all the solderings; everything looks fine.

I would appreciate any suggestions.

Thanks in advance.

Oihan

[sintech]

I think the trim pots will get you back on the right track.

[oyanliz]

Thanks for answering Sintech.

Moving the HMF trimmer of the card, the noise goes up or down in octaves (not easy to explain), but does not fix enything. Touching LMF trimmer, does not affect to the issue. I think is something regarding to the HMF, all the eq parameters work fine, Filter, HF, LF and LMF. When frecuency knob is set in a value from 3kHz to 7kHz, seems to works fine, but setting the knob lower than 3kHz, it sounds vibrating, ringing...
The same issue with 3 tested cards (tested in the same channel and also in each channel strip) and when replacing with a year ago recapped card (manufactured the same year, 1984) working fine...  I am not an electronics expert but it is very strange issue. I tried replacing C11 capacitor with 100uF 35v (Panasonic FC) but still it is doing the same noise. It seems a frecuency feedback or so...

Any help would be welcome.

Thanks in advance.

[Showcase]

Did the recapped cards work before?
Sometimes when this sort of things happen you could spot something if you reverse the procedure, it sounds like there is something fishy with your recap

...or if you have more to recap, do a couple caps at a time and check

[oyanliz]

Thanks for writing.

I still have 30 channels for recapping, but I am testing the 10 channels I just recapped. I don't know if the cards were working before as I bought a stored console (for 10 years). I'm still testing the recapped channels and there are at least 2 eq cards that they work. So the issue is not recapping, probably the eq cards had something wrong before recapping.
I will try finding what is wrong in these card (3 of 5 tested channels eq card are failing).

I will write back when I know something.

Thanks to all again.

Regards

Oihan

[walrus]

On the back of the 02 card are some resistors, 2 of which have some rubber sleeve insulation. On older cards, this rubber becomes conductive and will short out various tracks.
You need to replace the rubber with a modern day alternative. Other cards in the desk also use this older sleeving  and can suffer problems too.

[oyanliz]

Hi Walrus,

Thank you so much!! I knew that these rubbers give problems, but I never would think that the problem is the rubber in these EQ cards. I have changed the rubber to 2 not working cards and they work perfect now.
Will take in mind, for the issues I could find in the future.
I have attached two photos with the changed rubbers.

Best regards.

Oihan

[walrus]

No worries!   
I can't remember off the top of my head how many of the channel cards have links like this with rubber sleeving. But I know some of the centre section cards do, so it is worth checking them the next time you have to have this up.
Another problem I found when re-capping our desk is that some of  the old orange coloured caps had leaked onto the pcb causing corrosion.
This was especially so on the Dynamics card and again this caused some strange faults. You have to scrape the stuff off the tracks and then re tin them with solder.
In a couple of cases, the through hole plating had nearly failed, so there was a very high resistance from one side of the board to the other. Again just clear out the old solder and then reflow new in.

[oyanliz]

Thanks so so much!!

[waltzingbear]

In some cases it may be a good idea to add a piece of wire into the hole when soldering to provide something to solder too when repairing corrosion.

Cheers
Alan