DIYbanter - Magnavox rear projection TV RK8530AK02

Hi there!

I'm working on a Magnavox RK8530AK02 rear projection TV which has a
startup problem. The previous owner complained that the set would
intermittently fail to respond to the power button in an attempt to
switch the set on, whether with the momentary switch on the console or
with the remote. This intermittent behaviour gradually became worse.
Other than that, there were no other problems (no HV shutdown, no
problems with picture, no problems powering off, etc). Symptom has
worsened to the point that the set cannot be powered on. No audible
noises are heard and no apparent voltage drops on the main board when
power switch is pressed.

Contacts are good on power switch, line fuse is good, 120V AC is good
from primary transformer board to MAIN BOARD and to PTV HV POWER SUPPLY
board. Lithium backup battery on microcontroller is good (+3V). No
shorted electrolytic caps. I read an archived post about this set
whose owner was having the same problems as I am having now. From a
reply:

---begin quote---
From: Bill J )
Subject: phil/magn. 45" RP wont turn on....why?
Newsgroups: sci.electronics.repair
Date: 2000/04/12

First thing to do is with the set plugged in check Tp12 for approx 9
volts.
If low (5-6 volts) change C431,C460,C461. Also resolder connections on
IC305
(5 volt regulator).
If Tp12 has 8.5-9 volts then proceed to turn on the set and check Tp13.
Should be 12.5-13.5 volts. If not then replace C450 and C455.
One or both of these steps should get the set working. If not then post
further info and help will be forthcoming.

Bill J
---end quote---

On the main board, voltage on TP12 was -16.5 V; on TP13 was +120 mV
(near zero). These voltages were read using tuner shield as ground. I
resoldered IC305, which did appear to have a cracked joint, but this
did not fix the problem. I have not yet replaced the main B+ filter
cap, and having neither an ESR meter nor a scope, I cannot test its
functionality.

I would appreciate it if anyone who has information on this set could
reply with any pointers. Thanks for looking!

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