Recent content by djg

Where was the 15ohm resistor in series with the cap physically? I had only seen the one the schematic shows as load on +10V which I assume is the one we see in the second picture.

I would check the diodes forward voltage drop if you haven't. Those look like D664's that are highest failure rate component in R series logic. Then whichever is easier for you testing out of circuit or putting it on extender and seeing what is going wrong with signal.

I haven't seen enough theory to know. I did take some measurements on effect of capacitor value. Don't have equipment to change frequency. https://forum.vcfed.org/index.php?threads/capacitor-value-effect-on-ferroresonant-power-supply.1250770/

When I've wanted to fit a holder and modern are wrong size I have bought old caps online as long as I can see they say non PCB and protected and hopefully date to see if not too old. Mouser has one. Didn't check size. I would have to dig through old emails to see where I have bought what...

Look in the metal shield DEC 1016 in the second picture. I've seen them in there. Its oil filled with PCB and not protected so will spray boiling PCB oil when it fails. I've had multiple failures so replace them before trying to operate with modern AC capacitor. Hope it goes well. Would be...

On worry about stuff in water/if its really needed I think that's just one of the things that people will disagree about. Way to hard to do a test to verify. The machine was sitting in a barn for 50 years. Barn was deteriorating at the end. Mouse nest was on the power transformer. The steel...

I did similar for a barn straight 8. Washed with hose and soap and soft brush, rinsed, blew off most of the water with compressed air then let dry in the sun. May have hauled out a fan for more air. Compressed air can vibrate the wires so I kept some distance to reduce force on wire side. The 24...

https://www.mouser.com/c/?q=max232 $7 to $12. 75188/75189 around $1 so still a good price premium.

If anybody finds a part orderable from the US for the good pins please post it.

Full CHECKMO instructions http://www.pdp8online.com/pdp8cgi/os8_html/CHEKMO.WU?act=file;fn=images/misc_floppy/games.rx02;blk=381,34,0;to=auto

Nice discussion. Minor nit unless I'm confused. On slide 49 you say the SN75188/SN75189 are TI version of MAX232. The big thing about the introduction of the MAX232 was it no longer needed +-12V to generate proper RS-232 level. The SN75188 requires +-12V. It is the chip the MAX232 is intended...

Wikipedia A digital current loop uses the absence of current for high (space or break), and the presence of current in the loop for low (mark).[1] This is done to ensure that on normal conditions there is always current flowing and in the event of a line being cut the flow stops indefinitely...

All 33's I've worked on will chatter in line mode if loop is open. Won't hit print wheel or advance.

Start with motor since that is simple. The second pdf I linked to page 9/FS-9 shows the AC distribution. It just the line/local switch providing power to the motor. Page 27 has the switch terminals labeled. Is the motor connected to the terminal shown in the schematic? If so does the switch...

Like anything in the DEC world there are odd cases that are a pain to deal with. This is a single tape with 01600 blocks. DIAL has problems with the blocks past 01000. Your code gives DEC-12-SE2E-U0.linc.dsk: No DIAL or LAP6 directory found when it tries to see if it has a second index...