help with power problem

[davidh]

ok got a bad signal on a di1010 phase 1b
look at diagram
pin 11 should be 33v it is fluctuating
checked power back down the line starts off a 35v then drops right down
so
hmmm tuner removed checked power yess 35v
replaced tuner (off another board)
same problem


all help needed

 

[cob_ob]

sorrry can,t help you david as much as i would like to!!

 

[AtmelAce]

I think the volts go down from 33V as the box scans for a channel.... complex subject... The channels are spread from 1 volt to 29 V approx.
Dunno how it works cos usually, you apply a voltage to the tuner to select a frequency. This cable stuff seems to work the other way round. very confusing.
Maybe the tuning is done by SDA/SCL lines....

 

[davidh]

more to add to the saga

in engineers menu

dvb demod status
this is where the problem is

AGC COMBINED 218 signal low
SNR ESTIMATE goes from 27.5 - 34.5 db snr ok to marginal
PRE POST RS ERROR N/A
POST RS ERROR N/A
LOCK STATUS unlocked

mcns page all green

 

[davidh]

bump lol
anybody got an idea or is this box dead?????

 

[jake]

is it fluctuating when you are tuned to one channel , 5 for example , dont know much about cable tuners i thought they where pll tuned , looks like they are tuned by applying 0 to 30v to varicap diodes like tv , if you have changed the tuner and the problem is still there then suspect the chip that supplys the tuner with the tuning voltage , also check the other supplys to the chip as tuning is sometimes done by multiplying the voltage withing the chip eg. 12 to 33v, also check teh a.g.c pin for fluctuations as this has been known in tv and video to make the tuner go one way when it wants to go the other

 

[davidh]

is it fluctuating when you are tuned to one channel , 5 for example , dont know much about cable tuners i thought they where pll tuned , looks like they are tuned by applying 0 to 30v to varicap diodes like tv , if you have changed the tuner and the problem is still there then suspect the chip that supplys the tuner with the tuning voltage , also check the other supplys to the chip as tuning is sometimes done by multiplying the voltage withing the chip eg. 12 to 33v, also check teh a.g.c pin for fluctuations as this has been known in tv and video to make the tuner go one way when it wants to go the other

thanks for replying m8 no sorry the box wont boot
as on the pic the pin 11 should get 30v which it does lol but it varys meaning it scans the channels
but the problem is in the dvbmod section where i get mostly red
still looking for an answer if anybody knows or is it to the bin??
just seems a waste the box is sound but for this

 

[TBC]

hi davidh,

have you checked the 33v rail for noise/ripple, scope the 33volt rail and make sure its not dirty.
if you don't have a scope just tack a 50v 220mf capacitor across the 33v rail to ground. this should eliminate that problem if it is there.

infact wouldn't be abad idea to check the 12volt as well...

failing that you've got to take a look at the u400 TDA 6190X < but this has really got to be a shot in the dark but this is telling the tuner how to apply agc's ect.... is it also the same when you go through the channels in the eng menu up and down - if you can find one the locks, you can leave it at that channel and should be able to do a warm boot to a channels that is locked. you can with a 4001. never tried on a 1000p1b(1010p1b)

incidentally the 33volt line test point should be rock solid in the 33v range it feeds the tuners through resistors that should not allow it to be affected by actions at the tuner pin11. that is very strange (has the box been messed with by somebody already trying to solve the problem, because it sounds very unusual)