jsteiger

Ok, will try to trace through the relay circuit and see if I can find anything, thanks.
Are you 100% sure the zeners and 914s were not mixed up?
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110% sure!  I always double and triple check every component before I... er... hang on a minute... man these are hard to read... okay maaaaaybe CR1 and CR2 were swapped.  Wow, this sounds a lot better when it's not bypassed!

Thanks Jeff!  Amazing stuff as always.

Are you 100% sure the zeners and 914s were not mixed up?

Hi all,
I just finished my first of 2 LC25 yesterday but when i put in a DOA (Prebuilt JE-990 by Haibrall) PR5 and PR6 went up in smoke.
PR5&6 connect to the supply voltages of the DOA (+15, -15V) which I measured before. The DOA worked well in a Haibrall Lola and a CAPI VP28 before. Additionally to the burnt resistors the  the Output transistors of the DOA got really hot. I also measured that TP4 connects to ground, is that ok (via 2503?)?
I also checked the DOA on it's own ie connected it to a supply where each (+ and -) consumed about 2mAmps. I don't know where to look.

Greetings from Graz
« Last Edit: December 10, 2018, 06:59:07 AM by saturnjayzero »

jsteiger

Hi all,
I just finished my first of 2 LC25 yesterday but when i put in a DOA (Prebuilt JE-990 by Haibrall) PR5 and PR6 went up in smoke.
PR5&6 connect to the supply voltages of the DOA (+15, -15V) which I measured before. The DOA worked well in a Haibrall Lola and a CAPI VP28 before. Additionally to the burnt resistors the  the Output transistors of the DOA got really hot. I also measured that TP4 connects to ground, is that ok (via 2503?)?
I also checked the DOA on it's own ie connected it to a supply where each (+ and -) consumed about 2mAmps. I don't know where to look.

Greetings from Graz
Can you check again the resistance from the DOA output pin to ground? This should be a very low resistance so set your DMM accordingly.
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I fixed it. Your first instinct was right. One of the 99ers has gone bad.  The other one  of the pair i got works (for now, for a 99er).  Now I gotta find a cold solder somewhere in the relais-switching path. Those get triggered by the slightest vibrations. The gyrator switches seem fine but i suspect there will be another cold spot or two. Any idea how to spot them correctly?

The output pin resistance to ground was something like 10 to 50 Ohms if I remember correctly.

Thank you

So I checked all the solder joints on the switches and relais circuit. AFAICT The Unstable relais switch was caused by a cold solder joint at Q1. All the bands are working fine. My Problem now is that the unit emits a high-pitched hum. The hum is gone when I turn down the 1.6kHz band 4 dB. Jeffrey do you have any clue for me how to fix this? Also the unit seems a little bit noisy (even  with no source connected).

Best regards and Thank You for your help

Sorry Jeff, I got that too. Turns out testing a unit alone in the middle of a 6 slot rack can lead to weird radio interferences. That included the ringing noise and low humming every time my hand entered the inside of the rack.

I love the LC25 by the way. Such a powerful shaping tool. I had a lot of fun testing it out with my electric guitar. Can't wait to tweak some drums. Great job and a great kit. Cheers and good night.

jsteiger

Sorry Jeff, I got that too. Turns out testing a unit alone in the middle of a 6 slot rack can lead to weird radio interferences. That included the ringing noise and low humming every time my hand entered the inside of the rack.
What rack are you using? When we build them and test, they are wide open laying on a bench with a test jig. No enclosure. No noise or hum at all. That is why I am questioning the rack you are using.
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What rack are you using? When we build them and test, they are wide open laying on a bench with a test jig. No enclosure. No noise or hum at all. That is why I am questioning the rack you are using.

I have 2 racks by Rupert Neve Designs. I used a empty rnd r6 where i had the issues, Then i put it in a almost full rnd R10. I like them but they have no linear power supply afaik.