Proscan PS27123 (CTC169CG5) - need proper value of R3U

On the RCA CTC169, et al RCA chassis, they use R(4)xxx resistiv

designator assignments on their schematics, with the 4 being omitted o the chassis PCB screened markings .So, I'm definitely not seeing an R3U assigned as a valid designator on that line side raw DC powe supply's resistive parts list . Never- no- somehow, upon visua examination of an old "parts" retiree '69 chassis, now I do see tha R3U marking, all off by itself, just to the side of the SMPS ferrit cored power transformer T(4)102, on its side towards the PWM controlle IC, U(4)101. Otherwise, there are four 1 watt film resistors used i that SMPs's closed area. Two are mounted in the X-Y plane of the PC and two are set askew a bit. Two being in blue bodied casings and tw in pale green. Using your "given" initial digit 1 visual, the only tw of the 4, that might fall in that category, would be R(4)149 which i a 1.2 ohm 1 watt unit. It supplies the run voltage derived from th SMPS's secondary (after initial start up) to the discrete totem pol driver xstrs for the chopper xstr, and also, the full time run voltag for IC, U 4101's Vcc supply. How- some- ever, I can't see its failure (an overload opening) excep in the case of C(4)118 a 470 ufd/35VDC being bad, or the crunching o its derived supply rectifier diode CR(4)101 that comes off term #13 o chopper power transformer T(4)102. The second of the four resistors that would have a primary 1 digi would be the blue "askew" resistor that is floated just above th aforementioned resistor. It is the chopper transistor (Q(4)101' (mounted on the adjacent small heat sink) emitter current limitin resistor. It is a mere .18 ohm resistance of a 1W metal film type. Fo further ID info , you might check the individual end terminatons of th mystery res and pass back the info as to R/C/L parts designators tha are also commonly connected to its two end junctures.

Here is a very crude digital photo of the circuit board foil side. The resistor is marked in blue, the red arrow is pointing to the "R3U" designation.

Here is a very crude digital photo of the circuit board foil side. The resistor is marked in blue, the red arrow is pointing to the "R3U" designation.

Download the link on that page, run the exe to extract, then the exe for the 169 chassis. This should give enough information.

R3 is 33K and is part of the start up. Do a google search and check the capacitors that are commonly listed with your esr meter, c4108,4102,4104, etc.

David

Best call in a Pro ,when a resistor goes open usually something has caused it . Rebuild that SMPS section and disconnect the HVB whilst testing .Also look for coolant leaking.

Looks a little late on my up grade info but:

"OK with your further info on the resistor and the provided photo as to its interconnect. This time pulling out and consulting the fiche schematic instead of just the bare chassis visual, RCA designates that resistor as being R(4)003, so if the 4 is left off and the insignificant 00's left off, that would be R3 . That along with a half dozen other components in the front raw DC input stage.

That unit must have been quite hot to have opened and discolored that initial first orange band to look as a brown and left the center two unreadable. If you just figure a worst case of a full 175VDC being one end and the other end shorting to ground that would only account in little less than a watt being dissipated in that resistor unit....with a 2 watt rating on the unit..and it opening up? On a 169, in doing an initial topside visual of components, I don't remember ever seeing that 33k in anything but a pristine new look with no signs of heating stress or discloration. Had that unit been plugged in and had a dead short on its other side for weeks/months.....possibly, as there is power thru it as long as the AC line loop is complete.

And yes, RCA specifies it as being a 33K met film unit at 2 watt pwr rating. As you now may be able to see by the schematic reference, graciously provided to you by David.

That resistor is the bridge to initially power the SMPS IC and its internal totem pole drivers until the power supply kicks in and supplements the Vcc supply thru the term 13-14 of the SMPS transformer and its CR(4)101 diode . Also looking at all of the tie points of that resistor, the very lowest impedances to ground would initially be that C(4)178 470 ufd/35 V electrolitic if dead shorted. Following that would be the path to ground through R(4)149 a 1.2 ohm 1 w res thru a shorted CR(4)101 diode direct to ground. After that, the series resistive paths encountered would even further isolate the loading down...e.g. ..like the 22 ohms isolation provided if the SMPS IC should be shorted, etc.

This chassis typically will fail in two modes, like a hard crash with the failure of the SMPS chopper transistor or the SMPS IC in which case parts would be crunched and also take the line fuse.

An equally common failure mode ...typically with time...and this IS and old chassis... is the gradual

onset of high ESR in C(4)102 at the left side of the IC which filters the voltage sense line for the standby voltage function of the IC. Adjacent to that cap is C(4)104 which filters the current sense line to the shut down function of the IC. Off towards the heat sinks internal center side is C4108 that is coupling the drive signal into the chopper transistors base and filtering shot noise from the zener diode that it shunts. And lastly, you know about the power supply filter, C(4)178 .

The last scenario of changing out of the caps may result in a restoration of normal chassis operation with no prime power components crunched, since those electrolytics do take a continual hammering.

Keep us posted on progress. "

Had you changed all of the aforementioned electrolytics, and is the power

supply even trying to come up now or did some of the power components crunch.And is the hot component /smoke traceable ? And ,naturally, disregard the coolant leakage , as a 27123 DV set no havee.