RQDX3 (M7555) kills my system dead :(

[DrCharles]

I just spent a bunch of money on my PDP-11... specifically an RQDX3 (M7555). Reputable ebay seller, 3700+ FB with 100% positives.

It came in the mail today. Perfect physical condition except that someone had removed every jumper. Fortunately the DEC manual is online.
So I jumpered it up as shown in the instructions - and it kills my system (won't even come up to the boot prom dialogue, and the RUN light goes back off immediately). Also the red LED on the card stays lit, and according to the manual it should go off in 7-10 seconds when its power-on self-test passes.

It may be something I'm doing wrong, although it's a simple Qbus system and there can't be too many possibilities other than a defective card... I put it in different backplane slots, same result. Can't even run diags because the system is dead.

Your thoughts? Am I missing something obvious (to an 80's field engineer)?

 

[DrCharles]

Think I got it.
I found two pair of jumper pins in the middle of the board, not shown in the RQDX3 manual, which are connected to the two crystal oscillator cans (15 and 10 MHz).
They also connect perpendicular to the black insulator base of each pair of pins, unlike the addressing bits where the jumpers are parallel with their header-pin pair.
Anyhow I put in the one closer to the handle and now my system will boot again, AND 172150-172152 are visible both in ODT and map.
But the red light is still on.

So I put the other "undocumented" jumper in (I'll bet it provides clock to the floppy controller circuits). This time, after 6-7 sec. the red LED went out
The first RQDX diagnostic passed, but the others obviously fail because I don't have any drives connected yet.
Think it's OK now.

Wonder why DEC doesn't mention these jumpers? Maybe in the tech manual, I'll have a look.

 

[DrCharles]

I downloaded the Engineering Drawings (MP02259_RQDX3...) and sure enough, on the schematic there is a W20 and W21 jumper from each crystal oscillator to its associated circuitry. Including the DMA controller which explains why everything was dead on the bus.

But neither the drawings of the board, nor the jumper layout page, show them at all! It looks factory, too.
The original design schematic had a jumper and a 33 ohm resistor, presumably to control ringing on the fast edges.
The layout drawing shows the resistors but no jumper at all.
And the board I have does not seem to have the resistors, but does have jumpers.

Oh well, it passes ZRQDA0 test, anyway!

 

[AK6DN]

Those jumpers would have been installed by DEC manufacturing and then never removed.
Sounds like you had an overzealous seller that pulled all the jumpers for some unknown reason.