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Reference voltage lower that expected
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Reference voltage lower that expected

by Razvysme on Fri Jul 24, 2020 8:10 am

Hello,

I bought a partial kit from a guy on a FB group, and started building it yesterday, following the build manual and reading the wiki.

I didn't get far because the reference voltage range is between 4.1 and 4.8V, nowhere near the 5.333. I triple checked the resistors, unsoldering one leg and measuring them, and they all comply with the specs. The diodes are all 4148, and the shunt is LM336Z-5.0. Any idea what might be wrong? Below you can see how far i got. Cheerios.

IMG_20200724_140013.jpg
IMG_20200724_140013.jpg (357.86 KiB) Viewed 834 times

Razvysme
 
Posts: 5
Joined: Fri Jul 24, 2020 8:00 am

Re: Reference voltage lower that expected

by Razvysme on Mon Jul 27, 2020 7:01 am

I got some voltages reading:

d44 d45 juncture - 0.54
d45 r5 juncture - 1.08
r5 tm6 juncture - 1.72
tm6 r4 juncture - 2.22
r4 d46 juncture - 3.62
d46 d47 juncture - 4.16
d47 r3 juncture - 4.70
r3 r2 juncture - 7.50 (26.0)
r2 r1 juncture - 7.91 (29.0)

lm7805 pin 3 - 4.98
78l06 pin 1 - 5.98

Razvysme
 
Posts: 5
Joined: Fri Jul 24, 2020 8:00 am

Re: Reference voltage lower that expected

by MKRVR on Thu Dec 03, 2020 6:24 pm

Did you ever get any help with this?
I just started building a X0xbox kit from Willzyx (recieved it as a gift)
I have the same issue with reference voltage, no where near the required 5.333V. I only get 4.26 to 4.28V !

Seems like most of the responses and help are 5 to 10 years old. Is this forum still active?

Thanks

MKRVR
 
Posts: 1
Joined: Thu Dec 03, 2020 6:18 pm

Re: Reference voltage lower that expected

by Razvysme on Fri Dec 04, 2020 5:05 am

Yes i did. I ended up changing the resistors R4 and R5. Acoording to the power supply datasheet, the sum of the resistors needs to be less than 21k(if i remember well), so i just trialed different resistors until i got a good value. R4 is 6.4k and R5 is 1k. To make my life easier, i installed some single pin sockets so i could just swap resistors easily.
Attachments
IMG_20201204_100322.jpg
Resistors
IMG_20201204_100322.jpg (282.36 KiB) Viewed 669 times

Razvysme
 
Posts: 5
Joined: Fri Jul 24, 2020 8:00 am

Please be positive and constructive with your questions and comments.