e-licktronic Forum

Hello there,
I have a problem that I would need some guidance for.
I have started assembly on the Yocto board, passed the Power Supply assembly and completed the Noise section assembly.
At the point in the manual where you say

Test 4558 power. The red dot +15 V and green dot -15V (roughly 5%).

' I did so and everything checked out perfectly.
I then proceeded to install the opamp IC and the transistor.
At that point I proceeded to tweek the pot to arrive at the required ac voltage reading you specify in your guide as

Adjust the TM4 trimmer for 130mV on pin 1 of 4558. To measure, use a voltmeter in AC mode (AC)

.
This is where the problem kicks in: the minimum voltage reading on pin 1 I can achieve by turning the pot is 0.48VAC (instead of the =.13VAC you require).
I checked all the values of the components I placed into the board and they all seem right.
Do you have any pointers for me on where to look?
Here is an image of my board:

did you changed r131 to 100k and put 10uf 35v electrolytic cap in R127 from Roland service manual ? try this maybe will help

voltmeter in mV - 130mv not 0.13

BedroomMusic wrote:voltmeter in mV - 130mv not 0.13

Hi Bedroom,
thanks for the suggestion but I am using an autorange multimeter so the 130mV reading expressed in volts (0.13v) should be correct (130/1000=0.13).

BedroomMusic wrote:did you changed r131 to 100k and put 10uf 35v electrolytic cap in R127 from Roland service manual ? try this maybe will help

Hi Bedroom, I followed the instructions in the Yocto assembly guide. You are suggesting to use different values than those indicated in the e-licktronic guide? Is that what you did? Where is the Roland service manual to be found?
Ciao

service manual of tr808 and everything else about noise section you will find on the forum

http://www.ericarcher.net/wp-content/up ... vc-man.pdf --page 15

BedroomMusic wrote:service manual of tr808 and everything else about noise section you will find on the forum

http://www.ericarcher.net/wp-content/up ... vc-man.pdf --page 15

Hi Bedroom,

thanks for your feedback. I am confused however. Shouldn't the instructions and components in e-lictronic's be self-sufficient without having to go to an external document which is, incidentally, 25 years old?
Is the e-Lictronics assembly guide wrong?

I appreciate any feedback on this. I spent a lot of money on getting this board and the components and I am getting a bit worried...

Thanks
Marco

e-Lictronics assembly guide is not wrong is based on the original Roland tr 808 project and you can use service manual like in tr 808 you can mood yocto like 808 is 99% the same thing

if you have questions write to Vincent from elictronics ( send mesage from the side elictronics )

BedroomMusic wrote:e-Lictronics assembly guide is not wrong is based on the original Roland tr 808 project and you can use service manual like in tr 808 you can mood yocto like 808 is 99% the same thing

if you have questions write to Vincent from elictronics ( send mesage from the side elictronics )

Thank you Bedroom!

Update:

checked components one more time.
Found and corrected one mistake where (I must be becoming color blind) put in a 4.7K resistor instead of the correct 47K one for R127.

Ran the test again at pin 1 of the U24. Reading improved but still way off. Working the trimmer results in between 310mVAC and 380mVAC on pin1 of U24.
Replaced the U24 to make sure it was not defective: no change (previous chip was not defective).

Here is the voltage at all the pins to the U24.
Pin 1 : between 310mVAC and 380mVAC depending on trimmer setting
Pin 2 : roughly 61mVDC
Pin 3 : roughly 60mVDC
Pin 4 : -14.62VDC (note: reference on rail power supply voltage is -15.02VDC)
Pin 5 : roughly - 0.24VDC
Pin 6 : roughly - 0.23VDC
Pin 7 : roughly - 0.24VDC
Pin 8 : +14.64VDC (note: reference on rail power supply voltage is +15.03VDC)

The only anomaly I can now see is the drop in voltage between the rail power supply voltages and the effective voltages on pin 4 and 8.
Other than that everything else seems ok.

Any ideas on what is going on here?

Thanks to all who may respond/help in this matter.