[TechAssist] Re: RCA TV F20601SE CTC175A won't regulate 140V B+
- From: Al Gutz <alg@xxxxxxxxxxx>
- To: techassist@xxxxxxxxxxxxx
- Date: Wed, 06 Jul 2005 22:04:45 -0400
Gary
The collector supply for Q4153 comes from the +12V supply. What is the
voltage in and out of IC4102. If 15V going in and low on out maybe short
on 12V line.
Al G
Al's TV-Electronics
Pembroke Ont.
Canada
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
>
>
>
>
>
>
>
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