Monitor the collector voltages of q4153 and q4154. The voltages should increase and decrease inversely as the B+ goes up or down. If not suspect a bad q4153/4. If it does look at q4150. R4169 passes the 12v run supply to the collector of q4153 q4153 215495- smd, high failure q4151 146851 q4150 217309 The jungle outputs a regulator voltage. The path into the micro is the 141v supply by way of R4157 and r4163, in series, with r4171 and r4158 in parallel to ground at the r4163/r4157 junction. You also have 39k r4127 between U1001p29 and p30. Wayne Vanaman Omega Electronics 6904 W Fairfield Dr Pensacola, Fl. 32506-3310 Wayne@xxxxxxxxxxxxxxxxxxxxx WWW.PensacolaTVRepair.Com 850-456-5995 voice 850-458-6369 fax Gary McCartney wrote: > RCA TV F20601SE CTC175A won't regulate 140V B+ > > This set came in dead, with F4150 open clean (not black looking) and 12V > regulator outputting 6.2V only. Replaced these and eeprom plus power > tact switch. Now set will fire up when run on variac at 95V AC. > > I can't figure out why the power supply won't regulate at 140V. It will > go higher than 140V if I crank up the variac toward 120V ac.. > > Have done the following: > > -Replaced regulator output Q4150 with TIP122 > > -replaced Q4151 with MPSA42 (NTE287 exact) > > -replaced C4150 10uF 200V & C4155 2.2uF 200V > > -replaced Q4153 surface mount #215495 with MPSA06 surface mount > > -Measured R4175, R4155, R4150, R4153, R4154, R4152, R4169, all OK. > > -Measured: > > -12V reg out-ok, 4.8V on eeprom pins 6, 8 -ok, > > -U1001 pin 30= 3.7V -ok > > -U1001 pin 29 should be 3.7V -measures 5.2V but as viac is raised, the > 5.2V comes down close to 3.7V it should be > > -Q4153 B= 0.688 V, E=0V, C= 0.044V. C on SAMS schematic show it should > be 0.7 but I can't see why if the base is high, why C should read much > more than zero. My measurement agrees with me, not the schematic. Wonder > if mis-print or my mis understanding? Replaced this transistor with same > results. > > -Q4151 This transistor is not conducting because output of Q4153 is low. > B= .044V, E= 0V, C= 138V or whatever I have variac set at. > > - Q4150 reg out: depends where I have variac set but tracks the voltages > proportionally ok. No change since installing new part. > > -Q4151 This transistor is not conducting because output of Q4153 is low. > > Only other thing I can think of is to check the main B+ filter cap. > > Any other help appeciated. > > Gary > > > > > Gary McCartney > > McCartney Electronics > Guelph Ontario Canada > Est. 1984 > email: gary (at) number63.ca > > > > > > > > ----------------------------------------------------------------------------- > This Email List is Public. Remove: http://www.tech-assist.org/remove.htm > Set Vacation mailto:ecartis@xxxxxxxxxxxxx?subject=set%20techassist%20vacation > Lost Password: http://www.tech-assist.org and select "Login Problems?". > Email Archives: //www.freelists.org/archives/techassist/ > > ----------------------------------------------------------------------------- This Email List is Public. Remove: http://www.tech-assist.org/remove.htm Set Vacation mailto:ecartis@xxxxxxxxxxxxx?subject=set%20techassist%20vacation Lost Password: http://www.tech-assist.org and select "Login Problems?". Email Archives: //www.freelists.org/archives/techassist/