22-Dec-08: Wang 370

For a very long time, the museum has been looking for a Wang Laboratories 370/371 Programmer for the 300-Series calculators. The 370/371 is a system consisting of the 370 Programming Unit and the 371 Punched Card Reader. The 370 is a special keyboard/display unit that plugs into any Wang 300-Series calculator electronics package (although all features work only on the 360E, 360SE, or 362E electronics packages) that provides the standard function of a 360K/362K keyboard unit, but adds a bunch of programming-related functions. The 371 is a special punched card reader, similar in construction to the CP-1 and CP-2 punched card readers, but plugs directly into the 370 keyboard/display unit to provide the program code that the 370 interprets and passes on to the electronics package. The 370/371 system was developed to augment the very basic programming functions that the CP-1 and CP-2 Card Programmers offered by adding conditionals, branching, and looping capabilities, and the ability to control peripheral devices such as the Wang 372/373 data storage units.

Unfortunately, the 370/371 has proven to be extremely elusive. I have run across perhaps six or seven of these devices in over 15 years of looking, and of those that were available for sale (e.g. on eBay), all efforts to acquire them failed.

So, when I was contacted recently by Mr. Arnold Allen indicating that he had a Wang 360SE, Wang 370, and Wang 371 that had been sitting in storage for a very long time, I was intrigued. Mr. Allen graciously offered to donate the equipment to the Old Calculator Museum, which is greatly appreciated. 

Mr. Allen indicated that the machines had been in his possession for a long time, in excess of 20 years, and that they showed definite signs of age, and some signs of attempted repair.  The equipment was originally acquired by Mr. Allen as part of an auction lot that he purchased, with the Wang equipment being of secondary interest.  Fortunately, though, even though the primary reason the lot was acquired was for other items in the lot, Mr. Allen felt that this stuff was cool enough that he kept it around all these years.

The equipment was very well-packed and arrived at the museum without any problems.  Upon its arrival, the 370/371 was checked out.  The 370 is in darned good condition considering its age (the QA stickers indicate 1969).  There were indeed some signs that some non-professional repairs were attempted on the power supply circuitry of the 370 sometime during its life.  Also, one Nixie tube was missing.  The 371 was a little worse-off, but not too much so.  Someone at one point tried to replace the daisy-chain connector on the 371 card reader, and soldered it in with its placement just a bit off.  This resulted in the inability for the screws that retain the electronics circuit board in the card reader could not be installed, leaving the circuit board “loose” within the cabinet, retained only by the screws that hold the daisy-chain connector to the housing of the reader. 

The first order of business was to check out the power supply of the 370.  There are a total of N Logibloc circuit boards in the 370 that give it its local intelligence.  All of the boards were pulled, and inspected.  No signs of any catastrophic component failures, fortunately.  The was the usual layer of oxidation on the tin-plated edge connector fingers, which were cleaned using a contact cleaning brush and contact cleaner.  With all of the boards removed, some electrical tests of the power supply components were done.  The power supply transformed coils were tested for shorts and opens, with none found.  The rectifier diodes were also checked, with all of them testing good.  It appears that all of the diodes were replaced at some point, albeit a bit sloppily.  There is a 1000uf filter capacitor that was definitely a replacement also, and it looked good, and tested OK on the capacitor tester.  Two other can-type filter capacitors (3000uf) also looked like replacement units, and tested good.  The fuse was tested, and was good, so then AC power was applied via a Variac, with the line voltage slowly ramped up to 110V, while monitoring both the +11 and -11 volt DC supplies with digital volt meters.  The power supply voltages came up good, with the +11 reading +13.5V and the -11 at -11.9V.  Given that the supplies had no load on them, these voltages seemed reasonable. An oscilloscope was then used to view the power supply levels to check for excessive ripple, and, with no load, there was <1mv of ripple on either of the supplies, indicating that the rectifier diodes and filter capacitors were good.

After verifying that the power supply was working well, attention was turned to the backplane of the 370, to make sure that there were no bent pins or loose wires.  A detailed visual inspection showed that the backplane was in very good shape.  The cable/connector that goes from the 370 to the electronics package was ohmed out, and the connector inspected, and it looked to be in fine condition, with no broken or intermittent connections. 

The Logiblocs were re-installed in the 370, and power again applied (without the 370 being connected to an electronics package), and the power supply voltages checked under load.  The +11V supply was running at around +11.4V, and the -11V supply was running right on -11V.  Ripple was checked, and was only slightly more with the load in place, but still insignificant. 

Power was left on for a while, allowing the circuit boards to warm up, while the power supply voltages were monitored.  No signs of any problems occurred during this time. Without an electronics package connected, the 370 would not come up, as the high-voltage (180V) for the Nixie tube drive is supplied by the electronics package.The next step was to connect up an electronics package.  The museum’s trusty 360E electronics package was powered up with a 360K keyboard and tested to make sure it was still completely healthy, and it was found to be sound.    The 370 was then plugged into the 360E, and the 370 powered up, then the 360E powered up.  Some of the Nixie tubes started to light up – a good sign.  The PRIME key on the 370 was pressed to clear out everything, and zeroes started showing up on some of the Nixie tubes, and the + sign at the far left end of the display was also lit.  After letting the displays warm up for a while, there were two digit positions which refused to light up, but all of the other digits and the sign tube seemed to work.  Keyboard entry of digits gave the expected result, although after a little experimenting, it was found that the most-significant digit of the display had a problem. It would concurrently show the digit in that position, along with the digit in the 3rd digit from the left at the same time.  For example, if 1234567890 was in the display, the display would read +X2Y4567Y9Y, with the X being a “1 and 3” lit at the same time, and the Y’s being blank (with the least-significant digit having no Nixie tube in its socked). In spite of the display aberrations, performing math functions gave the expected results.  For the most part, the 370 was properly operating as a 360K keyboard/display unit just fine.

At this point, it was decided to focus on getting the display aberrations taken care of.  The two Nixies which didn’t light at all were removed from their sockets, and tested in space 320K keyboard that was known good.  They didn’t light up there, either, so the tubes were likely simply worn out.  These two tubes, and the missing tube, were replaced with spare, known-good tubes.  The 370/360E were powered up again, and this time, the display was completely lit, but the problem with the most-significant digit showing two digits at once still persisted.    Given the 300-series Wang machines’ propensity for edge connector finger and socket corrosion to cause problems, all of the cards were again removed from the backplane, and the edge connector sockets were cleaned carefully, but thoroughly.  After time for the contact cleaner to evaporate, the cards were reseated in their sockets, and the system was powered up again (again, without the 371).    This time, the most significant digit was displayed properly, with no “ghost” digits.  At this time, the full display was tested out, with all of the discrete neon decimal points checked out, and each digit ran through all of its combinations.  Everything worked perfectly.  The 370 is well on its way to recovery.

That’s all for this installment.  Check back for more on this story.

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