Adventure in fixing a Lisa DataPower PSU

[sigma7]

{AA, AB}    0.46, inf    CR18, CR19    AA:  0,0  AB: inf,0 

{7-9, 10-12}    0.46    Q2, Q1 e-c    0, 0 or 1
{9-7, 12-10}    inf    Q2, Q1 c-e    0,0
{8-9, 11-12}    0.46    Q2, Q1 b-c    0,0
{9-8, 12-11}    inf    Q2, Q1 c-b    0, 0

Please:

• confirm those measurements were made with the diode test function (if not, repeat using diode test), and
• repeat those measurements using the 200 ohm resistance mode of the DMM (so we have both the diode test and resistance measurements).

[berskyboy]

{AA, AB}    0.46, inf    CR18, CR19    AA:  0,0  AB: inf,0 

{7-9, 10-12}    0.46    Q2, Q1 e-c    0, 0 or 1
{9-7, 12-10}    inf    Q2, Q1 c-e    0,0
{8-9, 11-12}    0.46    Q2, Q1 b-c    0,0
{9-8, 12-11}    inf    Q2, Q1 c-b    0, 0

Please:

• confirm those measurements were made with the diode test function (if not, repeat using diode test), and
• repeat those measurements using the 200 ohm resistance mode of the DMM (so we have both the diode test and resistance measurements).

[/list]

Diodes   Fwd, Rev   Description   My PSU Measurements (200ohm)   Diode Test
{AA, AB}   0.46, inf   CR18, CR19   AA:  0,0  AB: inf,0     AA:  4 with beep, 4 with beep  AB: 3 with beep, 3 with beep


{7-9, 10-12}   0.46   Q2, Q1 e-c   0.6, 0.6   2 with beep, 2 with beep
{9-7, 12-10}   inf   Q2, Q1 c-e   0.4,0.4   3 with beep, 2 with beep
{8-9, 11-12}   0.46   Q2, Q1 b-c   0.6, 0.5   2 with beep, 2 with beep
{9-8, 12-11}   inf   Q2, Q1 c-b   0.4, 0.4   2 with beep, 2 with beep

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I was checking and found some replacement parts of the Q1 and Q2

https://canada.newark.com/webapp/wcs/stores/servlet/PFOrderCopy?orderId=RSyKGa2mSQ3syebQmY0AnBBWBThEJa2bnxY7%2fJ%2b0eR4%3d_IBM_2&langId=1&storeId=10196&catalogId=15003&URL=AjaxOrderItemDisplayView&CMP=e-email-sys-sendbask-GLB

[sigma7]

Unless you want to stock spare parts, it is probably best to determine exactly which components need replacement before ordering any.

To investigate further:

Desolder one end of CR18 and lift that end slightly from the circuit board. You only need to tilt it up enough that the end of the desoldered lead clears the hole in the board. One way to do this is to put a small screwdriver under one lead (on the component side of the board), and apply gentle leverage while heating the solder joint. If you use too much force, the component will break.

On this particular product, most of the component leads are bent over on the bottom before soldering. The lead that is less bent over will be easier to extract. In some cases, one needs to melt and remove as much solder as practical then straighten the lead where it is bent over on the bottom, then proceed to try to reheat and extract it.

If you have any trouble or are in doubt, post pictures of what you've got.

Once this is done, CR18 is only connected at one end, the other end is up in the air.

Then, using the diode test:

• On the component side, measure CR18 in both directions, and
• On the bottom side, measure between pads 10-12 (red-black), and
• On the bottom side, measure between pads 12-10 (red-black)

[berskyboy]

Once this is done, CR18 is only connected at one end, the other end is up in the air.

Then, using the diode test:

• On the component side, measure CR18 in both directions, and
• On the bottom side, measure between pads 10-12 (red-black), and
• On the bottom side, measure between pads 12-10 (red-black)

[/list]

1. On the component side, measure CR18 in both directions, and. = (Red to Black = 1, Black to Red 549)
2. On the bottom side, measure between pads 10-12 (red-black), = 0.5, and 2 with beep in diode mode
3. On the bottom side, measure between pads 12-10 (red-black), = 0.5 , 2 with beep in diode mode

[sigma7]

Excellent, that suggests CR18 is good. Leave it disconnected for now.

To further investigate Q1, on the component side of the board, beside CR18 locate Q1 (the silver part on a trapezoid shaped heatsink, (close to the big transformer with the copper wrap). Try removing the one phillips head screw attaching Q1 that is further from the edge of the board. If it just spins, stop trying and we will do something else.

If you can remove the screw, use the diode test to measure between 10-12 and 12-10 on the bottom side.

[berskyboy]

If you can remove the screw, use the diode test to measure between 10-12 and 12-10 on the bottom side.

between 10-12 and 12-10 = 0 coz the screw is removed.  The screw to remove should be closest to CR18?

with the screw closes to CR18 removed

between 10-12 and 12-10 = 2 with beep, and 2 with beep

[sigma7]

If you can remove the screw, use the diode test to measure between 10-12 and 12-10 on the bottom side.

between 10-12 and 12-10 = 0 coz the screw is removed.  The screw to remove should be closest to CR18?

The screw to be removed is farther from CR18, even better if you can remove both screws without difficulty, then use the diode test to check 10-12 and 12-10.

[berskyboy]

The screw to be removed is farther from CR18, even better if you can remove both screws without difficulty, then use the diode test to check 10-12 and 12-10.

with the screw removed you are not testing to a contact. (open circuit gives 1 on DMM).  Did you mean 10 to 11?  10-11 gives 2 with beep

[sigma7]

with the screw removed you are not testing to a contact.

With the screw removed, you should see: an empty hole, and around the hole is a solder ring, with a copper trace (under the green solder mask) that makes a short dog-leg to another solder pad about 0.5" or 1cm away. The solder ring around the hole is where the probe should make contact.

The intent is to measure what remains once Q1 is partially removed from the circuit.

So I expect that's what you did and when you measured 10-12 and 12-10, you found it was open circuit, that's fine. (Correct me/re-measure if I'm mistaken).

Then measure from 10 on the bottom side to the silver metal case of Q1 on the top side.

[berskyboy]

So I expect that's what you did and when you measured 10-12 and 12-10, you found it was open circuit, that's fine. (Correct me/re-measure if I'm mistaken).

Then measure from 10 on the bottom side to the silver metal case of Q1 on the top side.

correct open circuit DMM = 1
from 10 to the case (Red 10 to Black case) = 2 plus beep , 10 (Black to case) beeps and sporadic measurements

[sigma7]

Ok, let's compare with Q2.

Try removing the phillips screw closest to the edge of the board that is attaching Q2.

Then using the diode test, measure:

AB in both directions
7-9 in both directions

[berskyboy]

AB in both directions
7-9 in both directions

AB in both directions = 561, 1 (inf?)
7-9 in both directions = 2 with beep, 2 with beep

[sigma7]

Ok, it looks like both Q1 and Q2 are bad. You should remove them and test them out of circuit entirely.

Start by marking the cases of Q1 and Q2 with a marker or tape so you can keep track of which is which.

With all 4 phillips screws removed, each of Q1 and Q2 has 2 leads soldered to the board.

Once the leads are desoldered, slowly/carefully remove one of the transistors. If the heatsink comes with it, you can leave it stuck together; watch out for insulating nylon washers under the heatsink's screw holes. Otherwise (if the heatsink remains attached to the circuit board), there is a thin mica insulator stuck between the transistor and the black heatsink. The insulator is fragile and there is a thin coating of thermally conductive grease on both sides; it may remain stuck to the heatsink or come off with the transistor, or be stuck to both of them and be at risk of breaking. If you can keep the grease clean, then you won't have to do as much work to reassemble, so avoid touching it.

Once the transistor is removed, use the diode test and check all 6 permutations:

Red to Black
Lead 1 to Lead 2
Lead 2 to Lead 1
Lead 1 to case
case to Lead 1
Lead 2 to case
case to Lead 2

After the measurements, put the transistor and mica insulator back on the heatsink and circuit board (with insulating nylon washers if present) and insert the screws (slightly tight) to keep everything clean and not lose anything.

Repeat with the other transistor and measure it out of circuit the same way:

Red to Black
Lead 1 to Lead 2
Lead 2 to Lead 1
Lead 1 to case
case to Lead 1
Lead 2 to case
case to Lead 2

[berskyboy]

Once the transistor is removed, use the diode test and check all 6 permutations:

Red to Black
Lead 1 to Lead 2
Lead 2 to Lead 1
Lead 1 to case
case to Lead 1
Lead 2 to case
case to Lead 2

After the measurements, put the transistor and mica insulator back on the heatsink and insert the screws (slightly tight) to keep everything clean and not lose anything.

Repeat with the other transistor and measure it out of circuit the same way:

Red to Black
Lead 1 to Lead 2
Lead 2 to Lead 1
Lead 1 to case
case to Lead 1
Lead 2 to case
case to Lead 2

Q1
Red to Black
Lead 1 to Lead 2 = 2 beep
Lead 2 to Lead 1 = 2 beep
Lead 1 to case = 3 beep
case to Lead 1 = 3 beep
Lead 2 to case = 3 beep
case to Lead 2 = 4 beep

Q2
Red to Black
Lead 1 to Lead 2 = 3 beep
Lead 2 to Lead 1 = 3 beep
Lead 1 to case = 4 beep
case to Lead 1 = 4beep
Lead 2 to case = 3 beep
case to Lead 2 = 4 beep

[sigma7]

To me, it is odd that all 3 leads are shorted together, please re-check using the 200 ohm resistance mode.

One of the transistors is enough to confirm.