I experienced a strange, yet subtle problem, while adjusting ranges on the Datron when I had access to a Fluke
5700A 5720A series calibrator last month. The problem was unknown to me until the adjustment/calibration attempt. The instrument would accept the new adjustment then, when I wasn't looking, it would revert back to its previous value or something similar (
REVISED SENTENCE). You can imagine how frustrating this was after spending several hours meticulously adjusting each range and documenting the results to discover that the values were completely different after verification. Sometimes the value would even hold after a reboot! At first, I thought it might have been how I exited the calibration menu where it asks for the next calibration date (options being ENTER or QUIT). My hypothesis was that the digital board had some sort of malfunction in storing calibration constants. Although potentially unrelated, I should have taken more care in diagnosing the scrambled screen issue described in the initial post. I thought that the board might have been shorted because the card slot was damaged and the protective sheet under the digital board was a piece of tape and some card stock. Well, that was only part of the problem.
In a retaliatory manner
![Evil >:D](https://www.eevblog.com/forum/Smileys/default/xevil.gif.pagespeed.ic.tdrs7Uj5gu.png)
, I decided to replace all of the socketed components on the digital board to address the problem (what a beautiful design feature of the older Datron models). This is because I was unable to repeat the issue with a simple cause-and-effect process and I figured it wasn't that expensive to replace these components anyways. A Hong Kong-based eBay seller sold me nearly all of the obsolete parts required to do this swap (40 USD total with shipping). The rest were purchased new from DigiKey. Attached is a list of the socketed components that were replaced. I compared my older Datron to TheSteve's Wavetek model from what I could piece together from reference pictures.
Part of the replacement process involved programming 27C010, GAL16V8B, and GAL20V8B chips with the TL866II Plus and XGPro. I bought the TL866II Plus specifically for the GALs because my other universal programmer isn't that universal after all. Attached is a compressed file I used for the EPROMS and GALs organized into the socket designations. SHA256: 835656a4939d1b52c8f5afac1887858536df383ed417720487bb1cf1da4a9730 (checksum)
Another feature of the XGPro software package is that it can test some of the components through Device -> Logic IC Test, which can be rather helpful for isolating the program. I was able to rule out the 74245, 74374, 74165, 7404, 74260, and 74165 chips this way. The ROMs can be simply reprogrammed and then verified that they match a predetermined data dump.
At this point, I have adjusted my Datron to a well-determined Fluke 732A 10 V output and have not noticed a change in value since yesterday. The measurement error range is maybe +/- 0.2 ppm, at most, and is likely caused by thermal drafts. My next plan is to perform a fully automated test that will include a front input short (i.e., zero volts) and a reverse polarity test of a reliable voltage standard using the rear inputs (ChA and ChB) over several weeks at 23 °C.
![Fighting :box:](https://www.eevblog.com/forum/Smileys/default/fighting0030.gif.pagespeed.ce.H3HVtgjLEV.gif)