LisaList2

Quote from: berskyboy on Yesterday at 09:38:40 PMfound and bought from this site the 2N6308

Good choice!

It looks like there are very few TO-3 transistor packages still being made. The plastic case alternative will not be trivial to retrofit in the DataPower PSU.

I'm found and bought from this site the 2N6308

https://www.tedss.com/2028023156

Quote from: TorZidan on Yesterday at 06:24:06 PMmeasurement across two of their leads (forgot which ones) when they are soldered onto the board shows "a short", whereas, in fact, the transistors are fine. This is a major confusion when testing them.

Yes, that's a good point. In the DataPower PSU, the base drive for each of Q1 and Q2 comes from pulse transformers, with a winding connected between base and emitter. When attempting to check the b-e junction it looks like a short in both directions.

If I remember correctly, a continuity measurement across two of their leads (forgot which ones) when they are soldered onto the board shows "a short", whereas, in fact, the transistors are fine. This is a major confusion when testing them. Sorry, I have forgotten more details about this. I hope you can provide the details.

Quote from: berskyboy on Yesterday at 02:54:44 PMBut what about this value?:

C. ..

-no 0V, but I might not be putt the probe correctly

The fact that E - H show the SG3524 attempting to run indicates the soft-power circuit is working, so I think it doesn't matter if either you weren't able to probe it or my predictions were incorrect.

Quote from: berskyboy on Yesterday at 03:02:26 PMThis is what I found.

from AI or google:

Yes, the BUX48A can replace the 2N6308 in most high-voltage power supply

Neither AI nor google have any direct knowledge, they've only collected bits of information from elsewhere, and sometimes combine them incorrectly, so they can't be considered an authoritative or reliable source. eg. AI was previously telling you to replace a part that isn't there.

So I'm hoping there is a better source, if not, we will compare specifications in an attempt to confirm the suggestion is reasonable.

Quote from: sigma7 on Yesterday at 02:36:13 PMSo I suspect that replacing Q1 & Q2 (and ensuring there are no solder bridges remaining) is likely to be sufficient to repair the fault that blows the fuse.

The original 2N6308 transistors are no longer made, so finding a substitute is the usual option, although one could look for old-stock originals on eBay etc.

A few posts back, you referenced a Newark/Element14 cart with BUX48A transistors in it. Did you find references that indicate this is a suitable substitute?

Does anyone else have a recommendation for a currently available 2N6308 substitute that works in this PSU?

This is what I found.

BUX48A
TRANS, BIPOLAR, NPN, 450V, 15A, TO-3

https://canada.newark.com/multicomp-pro/bux48a/trans-bipolar-npn-450v-15a-to/dp/23AJ5969

from AI or google:

Yes, the BUX48A can replace the 2N6308 in most high-voltage power supply, inverter, and switching applications. It matches the package type, exceeds all critical maximum voltage and current limits, and provides equivalent or better switching speeds. Solitron Devices, Inc. +3

https://solitrondevices.com/datasheets/2n6306_8-ds.pdf

Quote from: sigma7 on Yesterday at 02:36:13 PMI'm assuming the "-" prefix in these readings doesn't indicate negative voltage... if it does then let me know.

that denoted a measurement.  Sorry I wanted to separate  it.

But what about this value?:

C. Turn off. Carefully (be careful the probe does not slip and cause a short circuit) hold the red probe to the lower end of R30 on the daughterboard (R30 is at the left edge/corner). The voltage should be near 4V.  Then while watching the voltage, turn on: the voltage should drop immediately to near 0. If the voltage remains high (around 4 VDC) then the soft-power circuit is suspect.

-no 0V, but I might not be putt the probe correctly

A pair of 2N6308 are used as Q1 & Q2 on the main board in the "DataPower" variant of the Lisa Power Supply, often referred to as the "1.8A" PSU due to the rating label.

This component does sometimes fail, but is not often a problem.

These transistors drive the rectified mains power through the primary side of the main transformer in a push-pull manner, controlled by the SG3524 on the daughterboard.

Quote from: berskyboy on Yesterday at 02:12:00 PM-1.631v to 9.72V then 1.63V (resistor to ground)

I'm assuming the "-" prefix in these readings doesn't indicate negative voltage... if it does then let me know.

The measurements E-H suggest the SG3524 on the daughterboard is attempting to drive the power circuit, so it is probably good. The other measurements suggest the ancillary circuitry is also working.

We haven't thoroughly checked the secondary side of the PSU, but since you have replaced the output capacitors, and we confirmed the rectifier diodes look like diodes, there is a good chance it is ok.

I suspect we found and corrected the original fault (a broken solder joint at the trimmer potentiometer R11), and the fault that caused Q1 & Q2 to fail, solder bridge(s).

So I suspect that replacing Q1 & Q2 (and ensuring there are no solder bridges remaining) is likely to be sufficient to repair the fault that blows the fuse.

The original 2N6308 transistors are no longer made, so finding a substitute is the usual option, although one could look for old-stock originals on eBay etc.

A few posts back, you referenced a Newark/Element14 cart with BUX48A transistors in it. Did you find references that indicate this is a suitable substitute?

Does anyone else have a recommendation for a currently available 2N6308 substitute that works in this PSU?

Quote from: sigma7 on Yesterday at 04:15:38 AMNormally, with Q1 and Q2 out of circuit (either completely, or with the 4 phillips head mounting screws removed such that their cases are disconnected), the main transformer will not receive any switching current.

In this state, the only output voltage will be +5Standby.

With the high power circuitry inactive, we can (hopefully) check some of the control circuitry without having a fault in the high power circuitry blowing the fuse.

Double check that Q1 and Q2 are disconnected (4 screws removed) or completely removed from the circuit board.

Ensure a good fuse is installed.

Connect the test jig load circuit to the card edge, and turn its small switch "off".

The small switch should still be in the OFF position, and the power strip will be on. Check the DC and AC voltages from pin 3 of the daughterboard connector to ground. This should be about 16 to 18V DC, and should have an AC voltage of less than 1V; if the DC and AC voltage are in that range, continue with the next step. If not, stop here, remove power, and report what you observed. If the DC voltage is about half or double, investigate whether the 115/230V jumpers are not installed correctly or damaged or not making proper contact. If the DC voltage was zero, check the fuse.

-DC: 17 V
-AC:  0.111 V

-Fuse OK

Remember to set the meter back to DC volts after measuring the AC volts.

Check the DC voltage across R33 (from one end to the other, not to ground)

-161V

 & across R2.

-161V

(These are two large resistors beside the large black capacitor C8.) They should be about 150-170 V each (positive or negative, depending on which way you probe them): if so, continue with the next step. If not, then the primary rectifier, line filter, and associated components are suspect - stop here, remove power, and report what you observed.

Check the DC voltage at pin 12 of the daughterboard connector to ground. This should be about 5V:

-4.97V

if so, continue with the next step. If not then Z2 on the daughterboard is suspect - stop here, remove power, and report what you observed.

Make sure the interlock switch has been engaged. Set the small switch (on the test jig connected to the card edge) to the ON position. There should not be any smoke, flashes, odours, blown fuse or other dramatic evidence of something happening. If something does, stop here, disconnect the power and report what you observed.

-ok

Collect measurements from the following steps A - H and report what you observe. As before, stop, disconnect power and report observations if anything happens that isn't expected.


These measurements are much more easily done if the black lead of the DMM can be secured to ground, freeing up a hand to operate the switch. eg. clip the black lead to the grounded side of a load resistor. If nothing else is available, inserting the black probe into the grounded mounting hole near the card edge connector and leaving it leaning against the edge may work. Be careful to not dislodge the probe while power is on; you might want to tape it in place. Turn off the power strip if you need to fiddle with this connection.

On/Off in the following refers to the small switch on the test jig attached to the card edge. The power strip can remain on (the behaviour of some of the following measurements is different if the power strip is turned off/on instead of the test jig's switch).

A. Turn off, locate pin 13 of the daughterboard connector (at the CR15 end), then while watching the voltage at pin 13, turn on: the voltage should rise from a low voltage about 0.5V to about 4.8V over a few seconds.

-0.388V to 4.64V (then stays at 4.6V)

B. Turn off, then while watching the voltage at pin 8 of the daughterboard connector, turn on: the voltage should rise briefly, from near 0 to near 5V, then return to 0. This takes less than a second but should be visible. If it is stuck at 0, double check the interlock switch has been bypassed.

-0.01v to 4.6V then down to 0.025v

C. Turn off. Carefully (be careful the probe does not slip and cause a short circuit) hold the red probe to the lower end of R30 on the daughterboard (R30 is at the left edge/corner). The voltage should be near 4V.  Then while watching the voltage, turn on: the voltage should drop immediately to near 0. If the voltage remains high (around 4 VDC) then the soft-power circuit is suspect.

-no 0V, but I might not be putt the probe correctly

D. Turn off. Carefully (be careful the probe does not slip and cause a short circuit) hold the red probe to the + (plus) side of C14 on the daughterboard (not far from R30). Then while watching the voltage, turn on: the voltage should rise over a few seconds from near 0 to near 4.8V. If stuck (around 0 VDC), then the brownout circuit is suspect.

-4.63V

E. Turn off, then while watching the voltage at pin 10 of the daughterboard connector, turn on: the voltage should drop from about 2.4V to about 1.4V for a noticeable but brief period (less than a second). If you don't see the brief drop, turn off, switch the DMM to AC Volts and when you turn on again, you should observe the AC voltage briefly rise from 0V to perhaps 1V (the value will depend on the DMM), then return to 0 before you turn off again. If no activity is observed, then Z2 on the daughterboard is suspect. Set the DMM back to DC Volts.

-goes 2.25v to 1.43v then back to 2.25v

F. Turn off, then while watching the voltage at pin 11 of the daughterboard connector, turn on: the voltage should drop from about 2.4V to about 1.4V for a noticeable but brief period (less than a second). If you don't see the brief drop, turn off, switch the DMM to AC Volts and when you turn on again, you should observe the AC voltage briefly rise from 0V to perhaps 1V (the value will depend on the DMM), then return to 0 before you turn off again. If no activity is observed, then Z2 on the daughterboard is suspect. Set the DMM back to DC Volts.

-2.25v then 1.84v then 2.25v

G. Turn off, locate R7 on the main board. R7 is on ceramic standoffs beside a silvery heatsink plate. One end should measure around 16-18V. While watching the voltage at the other end, turn on, the voltage should rise briefly, from about 1.6V to 5-15V (varies depending on the speed of your DMM), then return to 1.6. If no activity is observed, then Q4 or T5 is suspect.

-1.621v to 11.3V then 1.63V (resistor to ground)


H. Turn off, locate R5 on the main board. R5 is on ceramic standoffs near the center beside R4. One end should measure around 16-18V. While watching the voltage at the other end, turn on, the voltage should rise briefly, from about 1.6V to 5-15V (varies depending on the speed of your DMM), then return to 1.6. If no activity is observed, then Q3 or T4 is suspect.


-1.631v to 9.72V then 1.63V (resistor to ground)