Fluke 1953A Counter/Timer

I just purchased a broken Fluke 1953A Counter/Timer off of eBay.

Fluke 1953A

Fluke 1953A

This one I bought as broken for $32 plus $12 shipping. The Kenwood TS-530S I mentioned in an earlier post was supposed to be completely working, so this time I figured that I would just buy a broken unit and see if I could repair it. Before purchasing, I did look at the schematics of the unit, to get a good idea of the repairability of the design. I also did some google searches to see if I could come up with common modes of failure. There are a lot of counter timers on ebay. The reason that I settled on this Fluke was that this one had a oven for frequency control and the price was right. The oven maintains the frequency source at a constant temperature, so that fluctuations in environmental conditions don’t affect the accuracy of the unit. I found one site that listed the original list price of these units at $2295, I figured my $44 purchase was quite a deal. You can buy Chinese made frequency counters for around $100, but they wouldn’t have two channels and oven based frequency source and I doubt that they would have the long term stability of a relatively ancient Fluke.

When I received the unit, I decided to open it and take a look at the internals, before powering on. Inspection of the internals didn’t reveal any obvious damage, so I decided to power it up. Turns out it powered right on, but the self test didn’t work right. The self test uses the internal frequency source to drive the display. This wasn’t working right, as the displayed value wasn’t a consistent power of 10. After a bit of poking around and a power cycle, the unit didn’t power on at all. Now I figured that I had two problems to deal with, the incorrectly operating self test and the intermittent lack of power.

I found a note on a forum about a person that replaced a power supply cap to get his Fluke 1953A eBay find working, so I suspected that I might have a bad cap. I decided I’d pull all the power supply filter caps and test them out of circuit. I tested capacitance and found that all the capacitors seemed to have better than rated value for capacitance. Next, I built a simple ESR tester and ran that test on them. The 1000uF cap did seem to have a somewhat unusual ESR behavior. After spending a few hours trying some more iterations of the same tests, I finally came to the conclusion that the other caps were almost certainly good. I decided to replace the possibly bad one and found an equivalent replacement at a nearby Radio Shack. I installed all of them and proceeded to try to power on again.

Once again no display. I started probing with an oscilloscope. What I found, is that I didn’t have any power to the capacitors at all. Probing upstream showed that no power could be found past the on/off switch. After unplugging the unit, I unscrewed the nut holding the switch to the back panel and tested the switch with an ohm meter and found it that was faulty. Luckily I had an equivalent switch in my scrap box.

Switches

Switches

The switch on the left is the original. Note the damage on the top side and the long toggle. I’m guessing that this switch took a hit on the toggle which destroyed the switch.

I put the new switch in and powered on. This time the unit came to life, and even the self test worked. I’m not sure if the self test was fixed with the power switch swap or the capacitor change, but as long as it continues to work, I’m not going to pursue it further.

Testing accuracy against my Marconi 2218A reveals that after the oven warms up, the accuracy of the two units is within 10 Hertz thoughout their range. Take a look at this side by side shot of the two units.

frequency test

frequency test

Not bad, for a unit that was last calibrated in 2002. At some point I’ll work on getting the Marconi calibrated by beating it against WWV, after which I’ll be able to calibrate the Fluke against the Marconi.

Update – I just realized the Marconi has a limit of resolution of 10 Hertz, so these two units are, in effect, in perfect calibration with each other. I guess buying quality equipment does make a difference!

Upcoming blog posts

Too many projects, not enough time. I have some ongoing retro tech projects that will be described in upcoming blog posts. A couple automobile repair jobs have distracted me from more enjoyable pursuits, but those are behind me now. Here is a summary of some upcoming retro blog posts.

  • SCELBI PROM PCBs have arrived, I’ll need to build a card, burn EPROMs, and fire up my reproduction SCELBI and see if I can get MEA running
  • I bought a broken FLUKE timer/counter off of eBay and will document the attempts to repair and operate it
  • As part of the timer/counter repair, I built a simple capacitor ESR (equivalent series resistance) test device. As part of this effort, I also kludged together a simple capacitance tester
  • I also bought a couple of broken external 400K floppy drives for my MAC 128K, and will describe repair efforts
  • Bob Bishop’s Apple 1 Trade In Deal – and just when did Apple II’s first ship

    Apple 1 and Apple II programmer, Bob Bishop recently passed away. Though I didn’t know Bob Bishop, I did exchange a few emails with him in June of 2013. From the few emails I exchanged with him, I got the impression that Bob was a good guy, and I feel it’s unfortunate that I never got to meet him in person.

    Back in June of 2013, while refining the Apple 1 Registry, I noticed that at one time, that Bob had an Apple 1. I sent him an email, asking if he still had his unit. Bob replied, saying that he had traded it in. This was about the time that Fred Hatfield’s Apple 1 was sold at auction. There was much in the press about Fred’s Apple 1, which included a letter from Jobs, offering a trade in deal. This was a deal which Fred had refused. Bob was a little concerned that the trade he made, wasn’t as good as what Fred and others were offered.

    Here is the story of that trade in, in Bob’s words. The article he mentions, was a New York Times article that included some mention about how aggressively Apple pursued the Apple 1 trade in program.

    When I read that article, I was a little upset (and said so on my weekly radio show) to discover that the company had “an aggressive trade-in program, offering Apple II’s and sometimes cash incentives in exchange for Apple-1’s.” When I wanted to do MY trade-in, I had to go to apple and ask THEM if they would be willing to do it. They said YES… but only if I paid THEM some additional money! But I guess that was before they had fully started their trade-in program. So it may be that I have the dubious distinction of having been the very first person to trade-in my Apple-I for an Apple-II (since the serial no. of the Apple-II that I got was 0013). 🙂

    But now that you’ve showed me the original letter from Fred, It looks like the NY Times article may have gotten their information a little mixed up. According to the letter, it appears that Fred had to pay THEM the $400 — and not the other way around (just as in my case).

    I don’t remember exactly how much I had to pay when I made my trade-in, but I think it was about the same amount ($400). And I made the trade-in around late June of 1977, but Apple didn’t ship the computer to me until July. (I remember that they said it would be delivered to my home in the next few days. So on July third, I sat around anxiously waiting for delivey. The next day was going to be the Fourth of July, and if it didn’t come today, I would have to wait two more days to get it! Well, it didn’t come… so I had a very miserable Fourth of July that year. But around 10AM on July fifth, it finally arrived! 🙂

    – Bob –

    By the way, surviving evidence indicates that though Apple 1 trade ins occurred, it wasn’t a real great deal. Several surviving Apple 1’s that came through the hands of early Apple employees, were probably trade-in’s, but there aren’t that many of them. The only person that I know of, that actually acknowledged that he traded in an Apple 1, was Bob Bishop.

    SCELBI PROM PCB Update

    diode in copper

    diode in copper (crop of image by Jack Rubin)

    Last Friday, I thought I froze the layout for the final time. I took a few looks at it, checking for correctness over the last week, finding nothing to fix or improve upon. Today, I planned on kicking off the build, after doing a final check. However, during this “last” check, I noticed that the diode symbols were missing on the front copper layer. The are not obvious, as they are obscured by the actual diodes. I’ll have to add them in, recheck the layout, regenerate the Gerbers and do some final checking (yet again). Hopefully the PCB will be ready to order by Monday. After that, it will take about four weeks, plus or minus, to be manufactured, shipped, built and tested.

    Amateur Radio General License Exam

    In the USA, there are currently three classes of amateur radio licenses, Technician, General and Extra. Each advancement in class gives the license holder additional broadcast privileges.

    Yesterday, I passed my Amateur Radio (AKA HAM) General License exam. This gives me permission to broadcast RTTY data on a number of additional frequencies over the Technical License that I already held. Though I’m not entirely set up with the software and the hardware I need for RTTY, getting the General License is another step toward getting “on the air”.

    Since passing the General test, allows you free attempt at the Extra test in the same test session, I gave it a try. Out of 50 questions, I had 29 correct, 8 short of what I needed to gain an Extra license. Since I’ve gone this far, and am apparently pretty close to knowing enough to obtain an Extra license, I figure I might as well continue studying for a couple more months and see if I can obtain the Extra license.

    Posted in HAM

    Memory Test for the 8008 Posted on my 8008 Software Page

    This was ported to the 8008 from my 6502 memory test program by Mark Arnold. I have made some modifications to his port, so any problems are solely my fault.

    It contains a couple of enhancements over the 6502 version.

  • It does not stop on error
  • It keeps a running count of errors that is displayed every pass
  • http://www.willegal.net/scelbi/apps8008.html

    By the way it’s been running for the last hour, checking out the 12K of memory installed on my reproduction 8B, without reporting any errors.

    I suppose someone who needed a good 8080 memory test could port it to the 8008 or Z80 without too much trouble.