EB-1
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 p.1 #16 · whats a good cheap Flashs? | |
I'd like to correct some misinformation.  I have serviced and repaired 283/285 many times since the late 1970's. Unfortunately the service manuals are not immediately accessible, but I do still have them.  There were quite a few versions of the 283 made with changes to each of three main circuit boards, but nothing in the past >25 years uses direct high voltage to the synch contacts. The original version could have developed ~330 volts across the trigger terminals. Most DVMs will measure less than that because there is a voltage drop caused a high series resistor value (3.3meg?). The 600V reading reported was either a test artifact common with measurements of high impedance circuits, or perhaps the main capacitor was weak and parasitic oscillations were causing measurable spikes, etc. It not a normal static voltage at full charge. Later V283 models used a similar trigger circuit to the V285 in which the voltage was limited by a zener, usually 8.4V IIRC. AFAIK the V285 was electronic from the very beginning. However, I did not receive the very first version, so it is at least possible that some are not (I'd be willing to bet $$ against that though). I do still have one original (non-HV) V285 that has the low voltage synch circuit, so I know for sure that some of them did. Of course it is correct that the HV was low voltage.
A general note here is that voltage measurements should be made with the shortest possible leads to the device to reduce capacitance and static effects. Proper handling methods should be used when working with potential high voltages. Discharge the main flash capacitor with a 100-1000 ohm 10W resistor before proceeding to service the unit.
EBH
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