k4900 help please....

paul400

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trying to get this 4900 working, as you can see it needed some jumpers because of cracks on the board..capped it , looked for cold solder etc. voltage at the hot is 160vdc so.checked R363 tested good. R503 was 160vdc also. tested HOT and tested good. VR tested good. should i take some readings off the ic chip and if so what readings? what next to test?
 

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Since I am getting voltage at the vr of170 and at the hot of 170v that my jumpers took care of al the cracks?
 
No, that is for the K7000. The 4900 should be 130vdc at R503.


My mistake. On my K4915 B+ is 123V for 19" and 130V for 25". Since they are so similar and the manual lists 130V, I assumed they were identical.

Anyway, to the OP 160-170VDC at TP 91 is not good....
 
My mistake. On my K4915 B+ is 123V for 19" and 130V for 25". Since they are so similar and the manual lists 130V, I assumed they were identical.

Anyway, to the OP 160-170VDC at TP 91 is not good....


Yeah, his power is not regulating and so I'd suspect the voltage regulator first, checking all associated components while there.


I don't think I have ever seen a 4915 read only 123v, but I don't tend to check a system that is working. Are you sure you are looking at 4915 and 5515 (the WG designation for 25" med res 4900)?
 
Yeah, his power is not regulating and so I'd suspect the voltage regulator first, checking all associated components while there.

+1

Are you sure you are looking at 4915 and 5515 (the WG designation for 25" med res 4900)?

Yea, just rebuilt a dead 19K4915 in a SuperSprint. 19" uses an STR380 VR for 123V at B+. Don't have one, but my notes say that a 25K4915 uses an STR381 @ 130V.

EDIT: Your post made me question myself, and I just checked my old posts/notes. You are correct, a 25-K4915 does not exist and my notes should actually refer to a 25-K5515. That said, I triple checked and my SS has a 19-K1915 (19" med res) installed, the manual I have is for a 19K4915 and specifies 123V, and my service notes say that it tested at 122.5V
 
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Yea, just rebuilt a dead 19K4915 in a SuperSprint. 19" uses an STR380 VR for 123V at B+. Don't have one, but my notes say that a 25K4915 uses an STR381 @ 130V.

EDIT: Your post made me question myself, and I just checked my old posts/notes. You are correct, a 25-K4915 does not exist and my notes should actually refer to a 25-K5515. That said, I triple checked and my SS has a 19-K1915 (19" med res) installed, the manual I have is for a 19K4915 and specifies 123V, and my service notes say that it tested at 122.5V


Like I said, I don't doubt you. I check the B+ on every chassis I work, but I could have easily overlooked a properly operating chassis with a known good power output level, and since I primarily work on K7000s the two known good values are 123v and 130v. I'll pay more attention tomorrow when I test two standard res 4900 chassis...
 
update on this chassis, looking it over testing the resistors on the edge of the board all tested fine. i inspected the small transformer and noticed a hairline crack across on of its circuits, put a small jumper wire in and she fired up!! lesson learned, no bad parts or cold solder, just an open trace. next time i will go over the board with a bright light and magnifying glass.
 
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