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Too new to repair?
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legg
Sep 27, 2019, 8:44:05 AM9/27/19
to
Somebody brought in an RCA RLDED5098-D-UHD widescreen TV the other
day.
Damned if I could find service info or any spares on offer.
Though it looked like a small post-regulator wasn't running, to
prevent operation, there was no way to find out if it was supposed to
be off during a protective fault, or what the replacement parts were,
from smd coding alone.
It looked like the only alternative to the owner, for repair, was a
box distributor in the sticks of the greater Toronto area. This would
be complicated by a apparent lack of a serial number on the thing.
This is the first time I've run into this situation. From a service
manual information, I can generally do something.
RL
day.
Damned if I could find service info or any spares on offer.
Though it looked like a small post-regulator wasn't running, to
prevent operation, there was no way to find out if it was supposed to
be off during a protective fault, or what the replacement parts were,
from smd coding alone.
It looked like the only alternative to the owner, for repair, was a
box distributor in the sticks of the greater Toronto area. This would
be complicated by a apparent lack of a serial number on the thing.
This is the first time I've run into this situation. From a service
manual information, I can generally do something.
RL
John-Del
Sep 27, 2019, 9:55:31 AM9/27/19
to
Try disconnecting the TCON, the LED harness, and any remote and wifi boards and see if it responds differently.
Many of these use a particular start (ping-pong) sequence:
On plug in, the power supply standby supply turns on which feeds the standby voltage to the main board. The main board starts loading its software - this usually takes about 5 seconds on newer TVs. When the software is loaded, the main board then turns on the "run" supply of the power supply. The power supply turns on and feeds the run supply (typically about 12V) back to the main. The main detects the run voltage, shuts off the power supply and goes into standby to wait for a remote signal or the power contact to be pushed.
So if you see the "ps-on" line high and no 12V (just the standby 3.3V or 5V), the power supply is the problem, not the main. If the power supply ps-on line never goes high at any point, the main is bad or being locked up by a peripheral board.
It seems that there are two versions of that model; one has a separate power supply and main, and the other has them on one board. So if yours is a really low end toilet, the power supply is combined with the main board, so identifying control lines is a real problem. If you have an all in one it's best to troll the internet and look for a donor.
legg
Sep 27, 2019, 4:54:50 PM9/27/19
to
On Fri, 27 Sep 2019 06:55:28 -0700 (PDT), John-Del <ohg...@gmail.com>
wrote:
This had one main board with power and secondary-side signal
processing/communications/audio etc, with a smaller board interfacing
the led strings.
The PFC section (400v boost) was enabled, with four secondary-side
supplies ID'd as running (12v, 5v, 3v3, and 1v2).
UD3, marked GH6K, seemed to be the non-functioning postregulator - I
assume it would supply something between 5v and 1v2, considering the
lack of designer discipline in the selection of chipsb but couldn't be
sure it wasn't disabled internally.
As I've said, there's no sign of parts on offer for this thing, or a
manual.
RL
After a long power withdrawal, the unit could be convinced to give a
single lamp burst after start-up, but this was not evident in response
to soft on/off cycles. I assume that's latching protection of some
sort.
wrote:
processing/communications/audio etc, with a smaller board interfacing
the led strings.
The PFC section (400v boost) was enabled, with four secondary-side
supplies ID'd as running (12v, 5v, 3v3, and 1v2).
UD3, marked GH6K, seemed to be the non-functioning postregulator - I
assume it would supply something between 5v and 1v2, considering the
lack of designer discipline in the selection of chipsb but couldn't be
sure it wasn't disabled internally.
As I've said, there's no sign of parts on offer for this thing, or a
manual.
RL
After a long power withdrawal, the unit could be convinced to give a
single lamp burst after start-up, but this was not evident in response
to soft on/off cycles. I assume that's latching protection of some
sort.
John-Del
Sep 28, 2019, 5:30:10 AM9/28/19
to
On Friday, September 27, 2019 at 4:54:50 PM UTC-4, legg wrote:
>
> After a long power withdrawal, the unit could be convinced to give a
> single lamp burst after start-up, but this was not evident in response
> to soft on/off cycles. I assume that's latching protection of some
> sort.
Referring back to the boot/start strategy I mentioned, a very few models will also enable the backlight on briefly before the main IC decides everything is fine and go to standby mode. You may have an LED issue in the screen..
>
> After a long power withdrawal, the unit could be convinced to give a
> single lamp burst after start-up, but this was not evident in response
> to soft on/off cycles. I assume that's latching protection of some
> sort.
LEDs issues can be challenging. Some really cheap models use a single string of LEDs in series. Any open LED or an LED that is dropping more than it's nominal voltage (either 3V or 6V LED) will trigger either an over-voltage or under-current condition that will cause the LED driver IC to output an "alarm" to the main IC.
If you're lucky, there will be two or more channels of LED strings and hopefully they'll all contain the same amount of LEDs in each channel. If so, you can use an external tester like this one:
https://www.ebay.com/itm/New-330V-TV-LED-Backlight-Constant-Current-Board-Tester-Tool-Repair-TV-Led-Strip/392260386303?hash=item5b548a7dff:g:e-8AAOSwRFNcjO5H
Some TVs (many LGs) use a two channels system but run an odd number of LED strips for each, so comparing one channel to the other won't be of any help. One channel strings also leave no reliable reference to test against. Sometimes you just have to pull the screen and do an exploratory.
I would guess that your RCA is a two channel system using balanced strings. Disconnect the LED harness and use the LED tool to check the running voltage of both strings. If one string is open, you found your problem. If one string measures a few volts different from the other, that could also be your problem.
If you intend to work on TVs, you MUST have and LED tester. You can buy LEDs from Alibaba. I keep three types: 3V square, 6V square, and 6V "puzzle piece". You can also buy the complete strips and not have to deal with changing the individual LEDs, but this cuts into profit immensely.
legg
Sep 28, 2019, 9:49:04 AM9/28/19
to
On Sat, 28 Sep 2019 02:30:06 -0700 (PDT), John-Del <ohg...@gmail.com>
wrote:
I'm aware of LED issues - this one didn't seem to have an identifiable
power port for separate strings. The flash showed no open strings or
dull areas as viewded from the rear vents - hence my suspicion re LV
post regs.
The flash isn't repeated for controlled on/off sequences; only after
long delayed line power applications, so this is some kind of latching
hard fault.
The unit's not here any more - was in for free inspection/quote and I
had to admit that it was beyond current capabilities for competent
repair - no docs or spares.
Usually I can offer options, doc costs, or physical kluges to get the
thing up and running etc. There are sets out there now with 3/4
strings and slightly darker areas on the edges of the screen - simply
cheaper than relamping - gives owner time to consider replacement or
relamping as an option, without loosing their 'TV time', in the
meanwhile. For relamping, I refer them to guys who do it (and not much
else) all the time.
I haven't had a TV in my own home for decades, though the computers
are threatening to become/contain the same kind of rubbish.
RL
wrote:
power port for separate strings. The flash showed no open strings or
dull areas as viewded from the rear vents - hence my suspicion re LV
post regs.
The flash isn't repeated for controlled on/off sequences; only after
long delayed line power applications, so this is some kind of latching
hard fault.
The unit's not here any more - was in for free inspection/quote and I
had to admit that it was beyond current capabilities for competent
repair - no docs or spares.
Usually I can offer options, doc costs, or physical kluges to get the
thing up and running etc. There are sets out there now with 3/4
strings and slightly darker areas on the edges of the screen - simply
cheaper than relamping - gives owner time to consider replacement or
relamping as an option, without loosing their 'TV time', in the
meanwhile. For relamping, I refer them to guys who do it (and not much
else) all the time.
I haven't had a TV in my own home for decades, though the computers
are threatening to become/contain the same kind of rubbish.
RL
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