Racore Pwr Supply Repair

[chuckphd53]

Hi Chuck,

At some point I will probably upgrade my Quadram with the information you sent. I went back at the Quadram power supply and I could see the first band on the burnt resistor and it was orange. I measured the bad resistor and it measured 359 ohms so I thought maybe it only marginally changed value. Knowing that the first band was likely orange I decided that the original value was most likely 330 or 390 ohms so I dug out a 390 ohm resistor, soldered it in and it worked. The additional memory, clock, floppy and parallel port now work however Drive A was still and issue. I always had a problem with drive A whenever the Quadram was installed but it worked fine when the Quadram was removed. I had tried different cables and cleaning connections but that didn’t work so I was hoping that changing the capacitors on the power supply would fix this issue as well but it did not. But reading through the memory modifications for the Quadram you sent the last paragraph mentions issues with shielding. So I fabricated some shielding for the Quadram extension board and I was very happy that this cleared up the Drive A issue. I now have a fully functioning Quadram system.

Thanks again for the documentation.

Rick

I would keep an eye on the resistor, for heating. Also did you check the voltages for correct levels?
Nice to get one of these old specialty units back up and running, upload a couple pictures would love to see them..

Chuck

[RLumpy]

Yes I did check the voltage levels and they are spot on now. Ran the system for about 1/2 an hour and the R10 resistor never got hot so hopefully it is fixed now. Here's a picture of the shielding I installed.

[chuckphd53]

Nicely done.......

Is there an issue with noise, maybe let us know what the issue is!
I have not heard of this, but it is not hard to believe the boards are noisy....
did it cause issues or gremlins that have been documented by the users ?

even tho the Jr case does have a inside coating to capture the electrical noise.... poor mans Faraday Cage
it works

Chuck

[RLumpy]

There must have been some issue with noise causing problems with the floppy drive directly below the extender board. The original Jr. drive worked flawlessly with the Quadram chassis removed but had numerous read and write errors when the Quadram chassis was installed. I thought the issue was dirty connections or even bad capacitors but the documentation you sent me on upgrading the Quadram memory mentioned this problem. Here is that paragraph from the upgrade instructions.

"On newer Racor units the extender board that connects its memory
board to the sidecar has a solid copper ground plane over the bottom
surface. My system didn't and as a result, there was electrical
interference with the lower floppy disk drive, even before upgrading
the memory. The fix is to install a thin metal shield or plate under
your extender board and then solder a wire from it to a known good
ground. A folded sheet of aluminum foil connected to a ground clip."

My Quadram must have used the older style extender board as there was no solid copper ground plane as mentioned only numerous parallel traces from the edge connection to the connector at the other end. I used a sheet of soft gauze as an insulator and then a folded sheet of aluminum foil on top of that. I ran a ground wire from a pin on the connector and taped it too the aluminum sheet as aluminum doesn't work well with solder.

[chuckphd53]

Wow, reallyi formative, but not surprizing back then as everyone was rushing designes to the market..
thanks
chuck