Interm PA-9336

[TomHoward]

Hi all

I have a Inter-M PA9336 which is not 'half' powering on.

On power-on, the fan runs, but the power light doesn't. Removing either the internal ceramic fuse or the external glass fuse stops the fan running, so I'm guessing certain rails on the power supply are working, and others aren't?

My usual technical knowledge involves swapping out what looks burned or loose, so whilst my soldering and re-working are good enough my diagnosis abilities are non-existent. Any pointers gratefully received.

[g1]

Are you on 120V or 220V or 240?
The schematic shows 3 fuses, one of which is unused for 240V operation.

[TomHoward]

Hi

Thanks for the schematic.

We are on 240V here, I'm in the UK - the 6.3A is the externally accessible fuse near the power inlet, and 30A sounds right for the internal fuse as it was a heavy ceramic fuse. I think F3 the holder isn't even there on the EU model - I see those are in parallel which would make sense for the higher current on 120V.

A quick look at the schematic on the screen I can't spot the fan, but I'll print it out tomorrow and try find where a failure might be able to allow the van to still work but would prevent the rest of the board from working.

Thanks, Tom

[g1]

The fan is in sector C2.
In sector D3 there is a 7815 regulator, U13. One leg (input) is fed from the fuse F2 via R42. One leg has a 7.5V zener connected and should measure 7.5V. The output leg should measure 22V (TP11). I have a feeling the 22V may be missing or low.

[Jazz P Bass]

Yeah, the 22V supply is in Quad C-4.
Check the dc voltages at the + side of C30 & 31.

[g1]

Yeah, the 22V supply is in Quad C-4.

It's drawn a bit funny, 7815 shown with input on left, ground pin elevated by 7.5V zener so 15V reg. plus 7.5V gives 22.5V at 7815 output pin. Sector D3 .

[TomHoward]

Thanks guys

The 7815 reads about 3-5mV on each leg, including the ground and the input legs. However the fan is getting full 24V so the problem seems to be somewhere in between there. TP11 on the main board reads out at 3-5mV as well, positive legs of C30 & C31 the same.

What does the fan reading +24V but the input leg of the regulator reading almost nothing point to - I would expect to still see voltage on the input leg of the regulator if it was gone if I'm right? Only seems to be R82 and R42 between them?

[TomHoward]

Voltage at R82 is about 40V, and at the primary side of R42 is 40V-ish as well, but the secondary side of R42 seems to be about 4v, and R42 measures around 2M ohm, so I'm guessing unless there's a reason for that R42 might be the problem?

[Jazz P Bass]

Is R42 measuring 2Meg with one leg lifted?

Seeing that it's a 2 watt resistor, I would think that maybe the 15 volt regulator is bad too.

[TomHoward]

I've lifted one leg and actually it was the circuit around it that measures 2Meg, the resistor when lifted is open circuit.

I'm hoping the regulator is okay as I can replace the resistor without removing the board from the heatsink I think as it is stood off. I only have 1/4W 4.7ohm so I will order up a 2W as otherwise it will only last 5 minutes I guess.

[Jazz P Bass]

'Something' pulled more than 2 watts through that resistor.

Again, that leads to the regulator.
And what made that fail?

I would check all of the associated parts around the regulator.

My bet is, this is not going to be as simple as replacing a resistor.

[TomHoward]

Okay, not quite as simple as I might have hoped then.

Which other components would you be checking?

It's possible this might end up being beyond my expertise in the end.

[diydidi]

Check for shorted or "soft" shorted capacitors.

[g1]

If the 7815 is bad, it may have been taken out by a bad IC.
Check resistance across C23 and C20.
Don't worry, there's not all that much more beyond the regulator.

* Also, check R41.

[TomHoward]

Well I have swapped out R42 for a fusible 4.7ohm 2W resistor, so hopefully if anything is up then it should pop again without taking out too much else, and at the moment it's working okay - the three legs of the regulator now read 40V on the input, 7.5V ground and 22.5V on the output, so hopefully for the moment it seems okay.