Two Input Cards Same Caps Blowing Up

[MarconeMusic]

Hi All.

So, our new space is almost finished, but we have started to get the SSL up and Running. Had her Looked over by Roger Ginsley two days ago. Clean bill of health (in general)

I've noticed tho, two channels have had the same caps bulge out on the same card.

Any idea why?

its the 149 Card. from an E channel.
Card was recapped in the last year.

Both Cards have caps 13, 14 and 15 bulging up.

Im unsure if the cards are from the same channel strip. I dont remember but dont think that will matter.

Anyway Ill attach a few photos as well.

m

[amillar]

Unfortunately your photos won't open on my PC...are these the original 100V capacitors? If they've ever been replaced with lower voltage ones that would explain it, since these have the 48V phantom supply applied to them. Equally could just be old age (most of us start bulging around the middle once we're over 40 years old...). If anything's going to bulge on that card over time it'll be these.

Before I go any further, just to check: Is this the dual line input card, or the transformerless mic input card? I know the dual line card was called a 149 - and that's all I have a circuit diagram of - I couldn't remember if the transformerless mic card it was based on might also have (confusingly) been called 149?

Does anyone have a circuit diagram of the transformerless mic input card I could have a copy of?

Cheers,

Andy

[Chris Simon]

The 82E148 card is the the mic/line card (schematic attached).  Those caps definitely look too small to be 100 volt rated; is it possible that the 25V ones used elsewhere were accidentally installed here?

[Chris Simon]

Sorry, shoulda said 82E149.

[amillar]

Except for when it's the dual line card! Attached  (Sorry for the two sheets, I only have an A4 scanner)

It's because John East modified the mic/line 149 to produce the dual line using the same PCB, so we were stuck with that number literally etched into the PCB. For years I kept his original circuit diagram (which he designed in front of me), which was highly entertaining - coloured pen everywhere. I gave it back to him when he left, last time I saw it it was framed on his living room wall!

Many thanks for the circuit diagram!! 

Cheers,

Andy

[Chris Simon]

Many thanks for the insight, Andy. I had never come across an 82E149 card in a dual line configuration. These cards would appear to be mic/line cards, though, given the presence of D1-D4, the zener protection diodes for the mic input. In either configuration of the 82E149, caps C13-C16 are biased up with the 48 volt supply, and I still suspect those caps aren't 100 volt rated, leading to their untimely demise.

[amillar]

...I still suspect those caps aren't 100 volt rated, leading to their untimely demise.

Yes, that's what i suspect too

[MarconeMusic]

Heya!

Thanks for the wicked info guys!
Sorry for the late reply. I don’t get notified from here for some reason.

It’s the 82e149 transformerless channel amplifier.
Mono E channel card

So, from a quick convo with roger, we figured out exactly what you guys have said.

Some one put 25v in the position on few of my E channels!!!

At least all the ones I just randomly pulled out.
So, now I have to verify every card and solve this. Ugh.

We did this re cap like a factory, I desoldered snd soldered, engineers were populating cards based on a “factory” card and we were off.

We did 26 channels in a couple evenings.

Seems someone’s bucket of caps was wrong...
tho I did try and verify every card on the way in, I must have missed these ones.