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4001 diagnostics


DW Member ++
May 5, 2005
i posted this elsewhere and thought i would post it in my favourite place;

the 4001 reacquires its net id everytime it is powered up. if your box has gone ***** as a result of pulling red jumper then the upstream tuner is not working correctly.
the upstream tuner is used in langley boxes to get the netid. in a 4001 it happens each time the box is powered up. in the 4010 it only looks for a netid automatically if its stored netid is ***** i.e when you pull the red jumper.

when the 4001 starts up it goes through a cycle.
1 - PACE
2 - tune to home frequency TUNE (upstream tuner function)
3 - find network information table NIT (upstream tuner function)
4 - check for update info (if none then 8 else PAT) (upstream tuner function)
5 - start downloading update (from this point no engineering menu access) (upstream tuner function)
6 - erase current software(ERAS) write new software (LAIT)
7 - goto 1
8 - BOOT
9 - find last tuned frequency (downstream tuner)

as you can see from the boot sequence above there is a fine line in finding the problem because the boot sequence can be interrupted by atmel failure (stuck on pace) ram dries and faults (pace/tune ect...)
if the boot sequence is interrupted you could end up chasing you tail - especially when you working on a box that you didn't see go fault while you could still access the eng menu.
notice above that if you get to position 5 and the upstream tuner has less than 19db (you will not be able to access the eng menu at all - until you have repaired the fault) also the box will likely no longer have a record of its home frequency and so when the repairs are complete it will take some time to extract itself from TUNE at position 5 because it will have to do a sequential scan <takes upto 30minutes.

the operating range of the upstream tuner is minimum of 19db to acquire an update while a netid can be extracted at as low as 16db.
the downstream tuner function flawlessly at 29db upwards.

the cim module has a small socket on some 4001's for the rf loop through - i have noted a 2db drop when this is connected in the downstream tuner.

i hope you find this information useful - i notice above that somebody is claiming to have the diagrams for the 4001 stb and would appreciate it if they would share such information??
as i have been unable to acquire a complete 4001 diagrams.(this bit meant for elsewhere LOL)



Inactive User
Jul 27, 2005
Nice post, such great detail. Cheers