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Aleph3 clone offset problem
Aleph3 clone offset problem
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Old 10th June 2018, 03:25 PM   #11
Zen Mod is offline Zen Mod  Serbia
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Aleph3 clone offset problem
btw. I hope all testing and setting is conducted with outputs properly on heatsink .... so that picture is taken prior to proper mounting

just in case ......
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Old 10th June 2018, 04:47 PM   #12
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Hi Zen mod , The pot was set at 220 at starting point then trying to decreases R108 lower than 390R as you suggested.

mpmarino :they have insulator pad, do not touch each other. The good channel has be good since first SW on , without any VR to adjust. I just decided to add when fixing the bad one.


I believe heat sink is big enough.
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Old 10th June 2018, 06:31 PM   #13
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Aleph3 clone offset problem
tripple check all resistor values , orientation of parts etc.

maybe is wise to replace input mosfets ....... in case you succeeded in zapping them
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Old 11th June 2018, 03:01 AM   #14
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These input fet is second set actually. At First set, I got about 1.2V, cannot remember plus or minus, then reload second magazine and installed two VRs and get -3.7V. Ödo not know what to do next ......

I may take some parts out for check and re solder all joints again. Do you think where be a possibly bug area? I really hate to take part out /in through hole pcb.
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Old 11th June 2018, 06:16 AM   #15
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Aleph3 clone offset problem
when all parts are by prescription , with just two trimpots you must be able to set everything

positions are R108 , R113 , while everything else as shown on schematic , fixed values parts

leave it for few days , unburden your head , then be back with fresh energy

for starters just compare visually all parts between channels
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Old 11th June 2018, 07:56 AM   #16
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Not ...with Magnifier Ha ha....I will tell you some good news next week.
Thank a lot Zen MOD.
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Old 16th June 2018, 10:01 AM   #17
prakarn is offline prakarn  Thailand
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I changed the parts as you told on both channels. The situation are still same.
When turn the new POT 500R at R108 the DC offset can not be lower than -2.5V then fluctuate , LED dim down.

I reckon it might be have some malfunction or dead part there.

All compared voltage seem be okay except at the Q103 drain leg . It is about 6.7V but the work channel is only 3.5V.

What I should do next? thank you
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Old 16th June 2018, 04:49 PM   #18
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Aleph3 clone offset problem
voltages across Z103,R106 , R108 and across source resistors of outputs ?
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Old 17th June 2018, 01:26 AM   #19
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Quote:
Originally Posted by Zen Mod View Post
voltages across Z103,R106 , R108 and across source resistors of outputs ?
I measured after 10 min SW ON.


To give you more information , at Z103 be paralleled with 2.2 uf film capacitor and changed R105 from 4.75K to 3.3K as papa recommended on both channels.
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Old 17th June 2018, 07:50 AM   #20
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Aleph3 clone offset problem
-if input mosfets are OK,
-if there is no some wrong resistor value,

you must be able to set DC outout offset varying R108 ; in this case you need to decrease it's value (lower bank of mosfets opened too much)

with inputs shorted and no load ........ use multiturn trimpot for R108 , if you don't have steady hand , needed for single turn trimpots
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