andyp
Member
Guys,
I checked the 5 volt supply across the pins on an IC and got 4.4v and the voltage at the fuse before the 7805 is 10.2v.
I can probably get hold of an oscilloscope to see if there is any ripple and I think I've got a spare 7805 but what's got me a little confused is I appear to have a different set of component lists / schematic diagrams to those listed on WHTech. I can only assume that they were issued to me in the kit from Powertran. My sheets have additional hand written notes on them and there is a note printed on the power supply overlay saying :
* = vertically mounted 4R7 resistor (Drawn on overlay adjacent to BASE lead of Q1) and + = vertically mounted 100R resistor (Drawn on overlay between the COLLECTOR lead of Q1 and the output lead of the 7805 IC1) plus the comment "Fit only if the voltage is low (less than 4.8v on the TMS9928 )".
Looking at my power supply I must have experienced low voltage issues when I first built it because I have the 4R7 resistor in place but I then appear to have by-passed it at a later date probably because it didn't work and I couldn't be bothered to take the PSU out again to remove it.
It's all very confusing because they have not modified the circuit diagram so there is no way of telling exactly where these two resistors were intended to be connected. (I seem to have tried to fit the 4R7 in series with the 0 volt line of the 7805)
I realise that this description is probably very confusing, but using your expertise, where do you think a 4R7 resistor and a 100R resistor should be fitted to increase the ouput voltage - I am assuming that as they state the resistors are vertically mounted they are intended to be in series with two of the Q1 / IC1 leads but I don't know which ones.
The PSU component overlay also states that it is "ISSUE B" PCB.
I checked the 5 volt supply across the pins on an IC and got 4.4v and the voltage at the fuse before the 7805 is 10.2v.
I can probably get hold of an oscilloscope to see if there is any ripple and I think I've got a spare 7805 but what's got me a little confused is I appear to have a different set of component lists / schematic diagrams to those listed on WHTech. I can only assume that they were issued to me in the kit from Powertran. My sheets have additional hand written notes on them and there is a note printed on the power supply overlay saying :
* = vertically mounted 4R7 resistor (Drawn on overlay adjacent to BASE lead of Q1) and + = vertically mounted 100R resistor (Drawn on overlay between the COLLECTOR lead of Q1 and the output lead of the 7805 IC1) plus the comment "Fit only if the voltage is low (less than 4.8v on the TMS9928 )".
Looking at my power supply I must have experienced low voltage issues when I first built it because I have the 4R7 resistor in place but I then appear to have by-passed it at a later date probably because it didn't work and I couldn't be bothered to take the PSU out again to remove it.
It's all very confusing because they have not modified the circuit diagram so there is no way of telling exactly where these two resistors were intended to be connected. (I seem to have tried to fit the 4R7 in series with the 0 volt line of the 7805)
I realise that this description is probably very confusing, but using your expertise, where do you think a 4R7 resistor and a 100R resistor should be fitted to increase the ouput voltage - I am assuming that as they state the resistors are vertically mounted they are intended to be in series with two of the Q1 / IC1 leads but I don't know which ones.
The PSU component overlay also states that it is "ISSUE B" PCB.
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