Hello All,
It took a while, but today I was able to update my DSA 56A and perform a first test.
In my unit, one of the reference diodes are defect on the original 5001-0048b reference board. I decided to install a new reference board, based on the LM399. The new reference board fits in the same small box like the old one, and uses the same connections. To be able to use the original reverence supply I did adjust the output voltage to 18V, but this was not enough, as the old reference board was consuming less power then the new one especial at startup when the LM399 heater powers up. To be able, to get enough power at startup I modified the power regulator for the reference by decreasing the resistor responsible for current limitation. Original 16R was installed, now replaced by 3.3R.
On my Unit the CSA is also defect, and so I generated also a replacement for this board, based on the LTC2057 and the original output configuration with 2N2219 and 2N2905. Both schematic's are attached to this posing. Here I think is not mutch to say, have a look at the schematic - it is relay simple. as connection pins I used sub-d type male turned contacts, that have the same diameter than the contacts from the original CSA.
I did also an update on the power input port. I removed the direct connected line cord and made a cut-out for for an IEC input with integrated fuse holder. The internal line wiring, the transformer connection and the line switch have been insulated now. The line filter I left untouched for the moment.
First test after assembly looks promising. Next step will be a real performance check.
Please have also a view on the attached PDF documentation and photos.
Guido
Edit: spelling