attention if you power up your calrec eq (booom)

please be very careful when you connect the power cables to the pcb
don't exchange + and - !!

I did, so two electrolytics said "good bye" and exploded like a firecracker.... (f...!!!) :evil:

so I soldered two new 22µ caps to the pcb, but my EQ doesn't work

I measured all other tantal and electrolytic caps for their value...
they seem to be ok..

I changed all op-amps

but no sound is passing through



what other parts could be damaged by the incorrect voltage ??

resistors :?:

polyester caps :?:

ceramic caps :?:

... :?:

can electrolytics or tantal caps be defective, even if their measured value is correct ??

are you sure the supply voltages are correct (with dummy load?)
supply ground connected to star ground (pcb also)
supply is going to right 'holes' - trace the tracks to the nearest chips - plus on pin 8, minus pin 4.
you may have damaged the chips, but not unpolarised caps or resistors.

just first thoughts.

:evil: Sorry to hear about the reverse polarity.

Any Diodes close by in the circuit could have been exposed?

You might take a look at the schematic (if you havent already)
and see what components get exposed to the voltage first.

I think Tantalums may be more sensative to this rev pol.
Some of them have a polarity and if reversed may be damaged :?:

I also exchanged the diodes... I measured all values of the tant and electrolyt. caps (fine)

my other calrec eq is working

I pulled out the op-amps of both eqs and compared the voltages...

the op amps are getting its +/- 15 V on both eqs

but...

there's something strange !!

on the working eq the red marked area has 0,54 V

on the "dead" eq it's 0 V

but I really cannot find the source for the 0,54 V ??

http://www.soulset.de/forum/buggycalrec.GIF

That could be the offset in the opamp in this section. This is why we have the 33uF tantalums between each eq stage..

Try tracing your signal through the unit, to see where it disappears..

Jakob E.

thank you, jakob ... !!


I have run out of tant 33µ can I use 33µ electrolytics for testing ??

Anything from 22 to 100uF will do fine - including electrolytics. But for closest match to the original, use tantalums where marked..