SuperDrive 70’s Q3 collector voltage possible exorcism needed

[Anonymous]

Hi All, need some help to exercise some demons from my build….

I have followed and verified all the components are where they should be according to the build document.  When I went to set the voltage on the collector for Q3, I noticed there was no where close to the correct voltage of 5.2v .  I was too low (max 3.37v).

I did some troubleshooting but can’t see why I am having this issue.  Here are some of my findings.

Q3 P1= 7.24v, P2=3.92v and P3=3.37

Q3 pin 3 with Q2 removed =7.71

R17 on the + side =8.54v

R16 on the Q3 side=3.37 (see above)

R16 on the Q2 side=0.66v

C6 on the Q1 side 7.06v

C6 on the Q2 side 0.666v

I removed C6 and it tested fine.

I switched around all the transistors (Q1-Q4) and it made no difference.

All above testing was done with TR1 removed and no resister installed in R18

Any help or suggestions would be appreciated.

Thanks in advance,

Jamie

 

[Barry]

Install TR1. Adjust to voltage and audible sound. 3.37v is not that far off from 4.5v or a suggested 5.2v running it hot.

Don’t forget to do the same with TR-2 with the Drain of Q5. Try to get 4.5v to 6.5v

[Author]

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