Re: FG502 doesn't start at some specific settings


durechenew@...
 

For Mark,
I do not say it's not possible, but I believe no capacitor will warm up in a minute. Plus, there are conditions when it starts right-away (lower/higher frequencies).
There are (usually) two other plugins (DC502 and DM501A, great instruments - after some improvements) that always start and work without problem.
There is no IC in that stage.
A transistor with leakage current - one of the ideas I have in mind and didn't verify yet (specially Q204, Q210).

For Ozan,
Are +17V, "+17V (DCPL 1)", -17V, "-17V (DCPL 1)" on sheet <1> stable when cold (not working)?
Always stable (working or not) and (well) within spec, including ripple (I did a full calibration)

In the happy non-working state what are the voltages (partial list is OK if you don't have them all):
1) at the gate of Q200, and collector of Q292. As following: 1.124V at Q200-G, 1.116V at Q292-C (might be higher at gate of Q200, as I'm introducing in the circuit the input resistance of MM - 10 mohms; MM is a Fluke 179)
2) bases of Q230A and Q230B: -0.045V both
3) bases of Q290 and Q292: -9.01V both
4) emitters of Q140 and Q175: -6.47V at Q175-Base and 6.54 at Q140-Base (I don't have measurements for E, worth checking; but why would start at higher frequencies, same devices)

In case gate circuit is acting funny: Voltage at collectors of Q325 and Q315: I didn't verify if it's acting funny, but that circuit should have no influence as long as that input is without signal; and, again, why it starts at other ranges of frequencies?

What are the test points for the different traces?
Ch1: output of plugin (scope it's AC coupled, but no difference if in DC)
Ch2: Q292-C
Ch3: Q230B-B (Q230A and Q230B are pair in the same capsule, in my plugin; seems other SN had separated ones)
Ch4: Q230A-C (AC coupled, DC level is around -9V)
Thanks for comments, got something to think about and do tomorrow
TT

Join TekScopes@groups.io to automatically receive all group messages.