Agilent E3632A Repair

[gatatbat]

Hey, I hope im allowed to start a new thread to help try to solve my problem. I recently purchased an Agilent/Hp E3632A to attempt to repair. I'm not sure where I should start tbh. So far all I have to note is that the unit does not respond at all to the power switch. The display does not light up or do anything. I have checked the fuse and it is not blown. The other thing of note is when the power switch is on I hear a faint hum coming from the transformer.

[free_electron]

ever done any repairs of any kind ? these machines are not exactly the easiest to work on.

grab this : http://www.ko4bb.com/manuals/73.185.120.40/HP_E3632A_Service_Guide_-_Old_version_with_schematics.pdf

off the top of my head (i have repaired many of this series supplies)
if the display does not light there are multiple possibilities
- the display is cracked, vacuum gone and it's over.
- is there a beep during powerup ? if not :
-- the outguard cpu U4 does not come out of reset due to a blown gpib or serial port or missing 5 volt outguard (U10). this guy has to start first
-- the 18 volt rail for the display is missing:check VR1
-- check the outputs of U12 and U16
-- the POR supply has failed (U11) this is a device made by cherry semiconductors. VERY hard to find. if this thing does not start or generate the reset the supply will not start. it can be replaced by a LM2925
-- the display driver U1 or processor U7  is dead. especially if using the older NEC processor this is a problem. if they use the 8051 + TI driver those are fixable but you have to remove the display. supertex makes replacement drivers. SN75518
-- the communication between display and inguard processor is not working . check the lm339 on the display board. they get damaged often.
-- check the flash rom U13. take it out of the socket and put it back in. those sockets develop bad contacts. re-seating the rom solves this.
-- check the series resistors for the -13 volt suplpy on the display board. it's a chain of 4 resistors . they can crack or burn. if they open the 5 volt for the display processor will not work

working on the display board is very tricky as it is referenced to a 17.4 rail. everything "hangs" below so the 5 volt rail is actually -13v from ground ( the display "ground" is -17 volt ). this is due to the filament voltage for the VFDs. these display need to be driven by negative voltages. so HP designed this to "hang" under the main ground. the LM339 do the level shifting from the positive domain to the negative domain.

once communication between inguard (the 80188( and outguard /(8051 on display and another 8051 on GPIB) is established there will be a short beep.
outguard means the chassis ground referenced portion of the system.
inguard is the "floating" supply section including the main processor.


If this all passes the supply should start up with a live display.

oh , check that it is wired for 110 volt.... it wouldn't be the first one set to 220 volt if you are in the US...

[gatatbat]

I have done these kinds of repairs before, thank you for the helpful advice. I found that F1 and F2 are blown. I placed meters across them in amp mode and the unit powered on like normal. The schematic only refers to these as 1 so am I correct to assume that these are 1 amp fuses?

[free_electron]

yes. standard 1 amp 125v littelfuse part.
if both of them fried check  the tantalums c34 and c35. begind the regulators. they are right next to u12 and u16
 i've seen those turn crispy  and take out the fuses. they typically commit suicide and then take out the fuses. replacing the fuses makes it work again since the caps are now dead.
i hate tantalums with a vengeance...