Adventure in fixing a Lisa DataPower PSU

[berskyboy]

If you're having trouble getting consistent results, that seems like a good option. Then you've got two to compare if something looks odd.

As it is, unreliable measurements aren't very useful and it is hard to know how to proceed with troubleshooting. If you can figure out how to make the measurements repeatable/reliable say 10 times in a row, then post what you get, and explain what you figured out that you needed to do to get reliable results. (Without an explanation of what was wrong, future measurements remain suspect.)

ok sounds good.  Do you recommend a certain brand?

[berskyboy]

I got a new DMM let's try this again (I can try taking more measurements tomorrow). 

Q1
Red to Black. (diode test, 200 ohm test)
Lead 1 to case = 0L,0L
case to Lead 1 = 0.5, 0L
Lead 2 to case = erratic
case to Lead 2 = 0L

Q1
Red to Black. (diode test, 200 ohm test)
Lead 1 to case = 0L, 0L
case to Lead 1 = 0L, 0L
Lead 2 to case = 0L,0L
case to Lead 2 = 0L,0L

[sigma7]

I got a new DMM let's try this again

Excellent; to see how it behaves compared to the other one, try these measurements again using the diode test mode:

Diodes	Fwd, Rev	Description
{BA, BB}	0.13, inf	CR20a, CR20b
{DA, DB}	0.30, 0.37	CR25, CR23
.
Transistors	Red-Blk	Description
{1-2, 4-5}	1.25	Q4, Q3 c-b
{2-1, 5-4}	0.62	Q4, Q3 b-c
{1-3, 4-6}	0.70	Q4, Q3 c-e
{3-1, 6-4}	1.89	Q4, Q3 e-c
{2-3. 5-6}	0.64	Q4, Q3 b-e
{3-2, 6-5}	inf	Q4, Q3 e-b

And for each of Q1 and Q2 now out of circuit, also measure

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

Q1
Lead 2 to case = erratic

"erratic" implies a bad probe connection. Perhaps there is another explanation, but first try again and see if pressing the probes more firmly against the transistor makes the reading stable.

Also, avoid touching both points of contact while taking the measurement. eg. don't 'clamp' each of the probes against the transistor leads using thumb and finger touching the metal parts. You could squeeze one of the probes against a lead, but the other should not have a conductive path to you, as the current path through your skin can affect some readings. If you can avoid touching both, then thats the best option.

[berskyboy]

Excellent; to see how it behaves compared to the other one, try these measurements again using the diode test mode:

Diodes   Fwd, Rev            Description       Measurement
{BA, BB}   0.13, inf   CR20a, CR20b      BA: 0, OL BB: 0,OL
{DA, DB}   0.30, 0.37   CR25, CR23        DA: OL,OL DB:
.
I stopped because should I put Q1 and Q2 back into the PSU?

And for each of Q1 and Q2 now out of circuit, also measure

Q1
Red to Black         
Lead 1 to Lead 2.       0       
Lead 2 to Lead 1        0.1

Q2
Red to Black         
Lead 1 to Lead 2        0.8
Lead 2 to Lead 1        0.6

[sigma7]

Excellent; to see how it behaves compared to the other one, try these measurements again using the diode test mode:

I stopped because should I put Q1 and Q2 back into the PSU?

No, make these measurements with Q1 and Q2 removed, but that is a good question.

Diodes  Fwd, Rev            Description      Measurement
{BA, BB}  0.13, inf  CR20a, CR20b      BA: 0, OL BB: 0,OL
{DA, DB}  0.30, 0.37  CR25, CR23        DA: OL,OL DB:

And for each of Q1 and Q2 now out of circuit, also measure
Q1
Red to Black         
Lead 1 to Lead 2.      0       
Lead 2 to Lead 1        0.1

Q2
Red to Black         
Lead 1 to Lead 2        0.8
Lead 2 to Lead 1        0.6

Are those measurements using a "diode test" function? From the readings I'd guess it was a resistance mode.

So I can peruse the manual, what is the brand and model of DMM you are using now?

[berskyboy]

Are those measurements using a "diode test" function? From the readings I'd guess it was a resistance mode.

So I can peruse the manual, what is the brand and model of DMM you are using now?

Here's a photo of it. ASTrOAI CM2KOR
https://www.dropbox.com/scl/fi/2giwzufwhe0l051stcxix/ASTrOAI.HEIC?rlkey=b7got1wh776cwtdchmoxarybb&st=i8ld7461&dl=0

that was in diode mode.

[sigma7]

Here's a photo of it. ASTrOAI CM2KOR
https://www.dropbox.com/scl/fi/2giwzufwhe0l051stcxix/ASTrOAI.HEIC?rlkey=b7got1wh776cwtdchmoxarybb&st=i8ld7461&dl=0

that was in diode mode.

Test CR18 on the component side (one end still disconnected from the board) in both directions using the diode test mode.

Note the manual says on page 17 that to enter Diode Test mode, you have to press the "Func" button after rotating the switch to the diode test/continuity position. When in that mode, the diode symbol will be shown in the display.

[berskyboy]

Test CR18 on the component side (one end still disconnected from the board) in both directions using the diode test mode.

CR18 in diode mode
OL, OL

CR18 in resistance ohm mode
33.4, 0.45

[sigma7]

Test CR18 on the component side (one end still disconnected from the board) in both directions using the diode test mode.

CR18 in diode mode
OL, OL

Did you see the edit I made that says "Note the manual says on page 17 that to enter Diode Test mode, you have to press the "Func" button after rotating the switch to the diode test/continuity position. When in that mode, the diode symbol will be shown in the display."?

If not, try the test again in diode test mode.

[berskyboy]

thank you for that

CR18 in diode mode
0.462V, OL

[sigma7]

thank you for that

My pleasure.

Test Q1 and Q2 again, out of circuit, 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

[berskyboy]

Diodes	Fwd, Rev	Description
{BA, BB}	0.13, inf	CR20a, CR20b
{DA, DB}	0.30, 0.37	CR25, CR23
.
Transistors	Red-Blk	Description
{1-2, 4-5}	1.25	Q4, Q3 c-b
{2-1, 5-4}	0.62	Q4, Q3 b-c
{1-3, 4-6}	0.70	Q4, Q3 c-e
{3-1, 6-4}	1.89	Q4, Q3 e-c
{2-3. 5-6}	0.64	Q4, Q3 b-e
{3-2, 6-5}	inf	Q4, Q3 e-b

And for each of Q1 and Q2 now out of circuit, also measure

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

Now my new measurements:


Diodes  Fwd, Rev            Description      My Measurement
{BA, BB}  0.13, inf  CR20a, CR20b      BA: 0.126, climbing BB: 0.126,climbinng
{DA, DB}  0.30, 0.37  CR25, CR23        DA: 0.26, 0.277 DB: 0.267, 0.260

Transistors    Red-Blk    Description. My Measurement:
{1-2, 4-5}    1.25    Q4, Q3 c-b.  0.775, 0.767
{2-1, 5-4}    0.62    Q4, Q3 b-c.  0.572, 0.566
{1-3, 4-6}    0.70    Q4, Q3 c-e.  0.661, 0.681
{3-1, 6-4}    1.89    Q4, Q3 e-c.  1.583, 1.585
{2-3. 5-6}    0.64    Q4, Q3 b-e.  0.612, 0.618
{3-2, 6-5}    inf    Q4, Q3 e-b.  1.712, 1.725

Q1
Red to Black       
Lead 1 to Lead 2.    0v       
Lead 2 to Lead 1      OL

Q2
Red to Black       
Lead 1 to Lead 2      0v
Lead 2 to Lead 1      0v

[berskyboy]

Test Q1 and Q2 again, out of circuit, 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

Q1
Red to Black
Lead 1 to Lead 2 0v
Lead 2 to Lead 1 OL
Lead 1 to case 0v
case to Lead 1 0v
Lead 2 to case 0v
case to Lead 2 0v

Q2
Red to Black
Lead 1 to Lead 2 0v
Lead 2 to Lead 1. 0v
Lead 1 to case 0v
case to Lead 1 0v
Lead 2 to case 0v
case to Lead 2 0v

[sigma7]

Test Q1 and Q2 again, out of circuit, use the diode test:

Q1
Red to Black
Lead 1 to Lead 2 0v
Lead 2 to Lead 1 OL

Check this again, if it is a short circuit, it should be bidirectional.

With Q1 and Q2 and CR18 still out of circuit, do these again using the diode test (we are looking for additional problems):

Diodes	Fwd, Rev	Description
{AA, AB}	0.46, inf	CR18, CR19
{BA, BB}	0.13, inf	CR20a, CR20b
{CA, CB, CC, CD}	0.5, inf	CR1, CR2, CR3, CR4
{DA, DB}	0.30, 0.37	CR25, CR23
{EA, EB}	0.38, inf	CR26, CR24
{FA, FB}	0.41, inf	CR22, CR21
.
Transistors
Red-Blk		Description
{1-2, 4-5}	1.25	Q4, Q3 c-b
{2-1, 5-4}	0.62	Q4, Q3 b-c
{1-3, 4-6}	0.70	Q4, Q3 c-e
{3-1, 6-4}	1.89	Q4, Q3 e-c
{2-3. 5-6}	0.64	Q4, Q3 b-e
{3-2, 6-5}	inf	Q4, Q3 e-b

[sigma7]

Oh maybe you just did that... wait while I review