SYS 11 Display problem

[Mfresh]

I'm completely new to Sys 11 so any advice would be welcome:

The display on my Earthshaker refuses to display anything in the first digit position, on both top and bottom row. All the segments in the first position refuse to light. (In fact they do light very occasionally, but 99% of the time they are out.)

I have changed the display for a good one and there is no change, so it must be a hardware or connection fault on the display board, I am thinking. I have reseated the ribbon to no effect.

Any idea where I should be looking next?

Thanks!

 

[Jay Walker]

Hi,

I've just refreshed my memory of the System 11 hardware, and the furthest left digit on each of the glass envelopes seems to be Strobe 1, connected to the display pcb at J1, pin 9, Brown-black wire. The two sets of digit stobes are connected between the Cpu and display boards by their J1 connectors for No.s 1 to 8 and their J2's for No.s 9 to 16.

By "changed the display", am I right in thinking that another entire display pcb behaves the same?, If so, that points to a problem with the strobe, ST-1, on the cpu board. Both sets of strobes are controlled by PIA U 51, using decoder U44, with resistor packages SRC 7 & 8 between the decoder outputs and the connector pins.

 

[Mfresh]

Thanks Jay. I have indeed replaced the entire board and glass in the speaker panel with a new one.

The fault is definitely intermittent - but what should I be looking for if the strobe has a problem?

 

[Jay Walker]

The resistor/capacitor package, SRC 7, a thin strip which looks like nothing much, could be cracked or failing when warmed-up. The seven of these on the circuit board are all identical.

 

[Mfresh]

You are absolutely right that once the machine has been running for 10 minutes or so, and the components are warmed up, it's then that the first digits stop working.

I can't see any physical damage to SRC 7 (or SRC 8), but do you think that I should replace them as a first step? If so, any idea where I can get them - part 5060-10396-00 - in the UK.

 

[Jay Walker]

Some 'freezer' spray may help to establish which component is failing when warm. Applied to each component in turn, a temporary improvement would show up the culprit.

Apart from borrowing' an SRC package from a spares/leakage damaged board, RS or Farnell may stock such devices, but I think the former is account only, and the latter had a minimum order the last time I bought anything there.