the MRH Forum

MICRO DESIGN COMBO PCB REV 1.0 MRH magazine help
Reply
New member 2 posts tassailor New member 2 posts
tassailor

Found these on a layout being dismantled.  Does anyone know what they are?

part%202.jpg part%201.jpg 
Reply 0
eastwind Super User 3,613 posts
eastwind

I looked up the chip -

I looked up the chip - googled MC68HC705J1A.

It's a motorolla 8-bit microprocessor system on a chip, presumably descended from the motorola 68k processor.

64 bytes of RAM, 1232 bytes of EPROM.

Whatever it's doing, it's not much.

You can call me EW. Here's my blog index
Reply 0
ACR_Forever Prolific poster 1,363 posts
ACR_Forever

How they were installed and what they were connected to

might have given more hints, presuming the installation was complete (I suspect layout abandonment before completion, given so many connections aren't wired yet, as evidenced by the lack of solder and wire stubs in the holes).  Components all date back to pre-turn of the century.  My first guess would be some form of block sensor, given it has both track buss legs in and out (with beefy power components inline both sides), and a DC rail  that powers the MCU.  Eight power semis(four on each DCC leg, so my bet is a form of bridge rectifier construct providing a double-diode voltage drop for current sensing), three optos, two likely for power isolation and one likely for an isolated output, possibly a 555 variant, and an LM393 amp.  Don't see any form of power regulation, so it may require a good 5V rail as input.  One status LED, three outputs. 

So, possibly, a combo block sensor and signalling element, though there's no sign of LED drivers for signals.  Or maybe, a block sensor for staging yard tracks, for providing occupancy indication? 

My 2 cents.

Blair
Reply 0
joef MRH Founder 17,480 posts
joef

The sad truth

The sad truth is you’re looking at boards using 30 year old electronics with no instructions for their use. Thirty years ago the internet was still a research project, TVs still used picture tubes, and VHS tapes were all the rage. A portable phone was the size of a large milkshake and the Macintosh had just come out with a full color screen. Tablets and smart phones were still a couple decades away. A good PC or Mac cost $2000+ and having a megabyte of memory was considered awesome. Having a one gigabyte hard drive was tons of disk space. Cameras still used film — digital still cameras were still years away. Digital video was even more years away. Whatever they do, modern electronics almost certainly does it far better and at less cost than these were when they were new. In fact, I’m willing to bet one $30 Raspberry Pi or a few $5 Arduinos will run circles around the entire collection of all these boards.

Joe Fugate​
Publisher, Model Railroad Hobbyist magazine

[siskiyouBtn]

Read my blog
Reply 0
tassailor New member 2 posts
tassailor

Response

You guys have nailed it, very helpful.  Old junk circuit boards, most likely an early form of block detector.

thanks.
Reply 0
jhaverty New member 1 post
jhaverty

Actually those look like Auto Reversers

FYI, if anyone still has these, they are likely still useful.   It's a "Power Shield Auto Reverser" from Tony's Train Exchange.  They still offer a newer version for sale, see https://tonystrains.com/product/dcc-specialties-psx-ar-power-shield-auto-reverser-circuit-breaker  But the old ones work fine too on my layout.

Here's the User Manual for the old PS AR (2 pages)

PSAR-1.jpg 

PSAR-2.jpg 
Reply 0
Reply