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jaquinn@ihug.co.nz http://twitter.com/jaquinn| Fixing the FT-101ZD Digital Frequency Display |
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| Written by Administrator |
| Tuesday, 26 February 2008 17:59 |
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In my previous post I talked about my "new" Yaesu FT-101ZD. I had purchased it knowing that the digital frequency display was faulty and the seller included a Jaycar frequency counter kit. I wanted to keep the rig a bit more original and was planning to build my own frequency counter using an AVR (or similar) microcontroller and use the existing 7 segment displays (or replacements if they provided to be faulty). My ZD is a -16 serial number so was in the first batch to use the new frequency counter based on the MSM9520RS chip. From comment on www.foxtango.org it appears that failure of this chip is not uncommon. There is also a kit for a PIC based replacement from Teruhiko Hayashi (JA2SVZ). Having more than enough projects in the queue I decided to go with Teruhiko's kit rather than reinvent the wheel. Having ordered, built and installed the kit I have no hesitation recommending this to anyone wanting to replace the MSM9520RS in their transceiver. The kit arrived promptly (Japan to my rural QTH in NZ took 4 days), was very well packed, included printed instructions (even through they were available on the internet) plus extra data on pin mappings, voltages and resistance to be expected which would be a great help fault finding plus Teruhiko appears genuinely concerned that you will be successful with the kit... we had a number of emails conversations where he provided hints and suggestions... particularly around removing the MSM9520RS which with 40 pins can be fun to unsolder.... the easiest option (and what I did) assuming you don't want to keep the chip for a museum is to cut the leads to remove the chip and then clean the cut legs from the holes. If you are going to build the kit you need a fine tipped soldering iron (it makes assembling the PIC/MSM9520RS adapter board without solder bridges so much easier if you iron is fine tipped), a solder sucker (to clean out holes on the PB-2086 frequency counter board) and a set of side cutters (so remove the MSM9520RS and to trip excess leads from newly inserted components). Here are some photos showing assembly steps: 1. The assembled adapter board that allows the PIC to be used in place of the MSM9520RS.  2. The PB-2086 Frequency Counter board with MSM9520RS and other misc components removed and ready for replacements to be inserted.  3. The PB-2086 Frequency Counter board with replacement components (excluding the PIC) and ready for installation. Initial install was done without the PIC so voltages on the adapter board could be checked with no risk of damage.  4. .... And the end result..... a working frequency display. I still need to calibrate it which requires adjustment of the trimmer on the PB-2086 so will do this in the coming week by visiting a friend with an accurate frequency generator. Looks good eh!  As shown in the picture there is a slight mismatch between the counter and the VFO dial... I am sure this will be corrected once the alignment is done. My next project after consultation with more experienced operators of the 101ZD is to replace the electrolytic capacitors on the PB-1968 rectifier board. These are getting on a bit and failure might have some significant downstream effects. The Fox Tango web site has some very interesting 101ZD information and one PDF of particular interest is a re-review by G3LLL. . I found this interesting because it makes specific mention to check that the fuse that is installed is correct (3 amp quick blow for 234 Volts in NZ) so any failures have less chance of doing real damage. I checked mine and found the fuse was 7 amp! Remember to check yours....... The project list after the PB-1968 board is done includes.....
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