TEK 465 S/N>25000 Power Supply Issue


Craig Cramb
 

Got a 465 that was somewhat functional but no trace with blown F1419. Went thru Groupsio file library and replaced the C1419 and that got the signal trace. Reviewed the Power supply and here are the original results.
-8 =7.79vdc, 265mvAC
+15 =13.13vdc, 2.26 mvAC
+55 = 53.7vdc, 1.8 VAC
+5 =4.88vdc, 156 mvAC
+110= 110.9 vdc 1.8 VAC

Decided to recap the unit with all input PS filter caps. Got this completed and then I had this result.
-8= .585vdc .4mvAC
+15=1.6vdc .3mvAC
+55=46vdc .7mvAC
+5= .788vdc .3mvAC
+110= 107.3 vdc , 6.2mvAC
Replaced the CR1541

Started trying to determine the possible issue and determined that I had no +22vdc at U1524A&B input. So continued on going thru the +55 regulator and determined that if I left pin 1 out of the U1524 base socket the +22 vdc would show up. So then re-socketed the pin 1 along with all others and it would drop +22 again to 2.26Vdc. So I moved to the B section of chip U1524 and removed pin 7 with all the others in the socket the +55 V would go to 54.9vdc. At this point decided to move onto the +15 section of the regulated supply. Went thru and disconnected jumpers, and plug connectors checked components as per the troubleshooting of the +15,+5,-8 in the manual. Rechecked with power applied and the voltages all went back to the low value readings. Traced it down to the Q1544 transistor when it was removed the U1524 amplifier voltages would come up to as the markings in the manual for voltages except for the lead 6 of the U1524B. Swapped it out the Q1544 with no change. So now if I just disconnect the base of transistor Q1544 +55 and voltage readings around the U1524 a&b are as needed along with the +55. Thinking that the Q1546 is causing the issue. As I have basically gone thru and checked all the resistors, capacitors and diodes involved in the circuit down to the TP1548 +15VDC. Including the Q1546 and don't see any issue.

Any thought are welcomed on this issue.
Craig

Join TekScopes@groups.io to automatically receive all group messages.