I won a local auction for an Apple Lisa!!!

[berskyboy]

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

Q2
Red to Black
Lead 1 to case = inf
case to Lead 1 = inf
Lead 2 to case = inf
case to Lead 2 = inf

These two sets of readings don't agree with each other.

The diode/continuity test says these are a short circuit, and the ohms test says these are an open circuit.

Can you figure out why? I presume the issue is my instructions are ambiguous in some way.

I see the meters from that company do contain fuses, so perhaps the fuse is in the ohms circuit... if you touch the DMM leads together does it show a short circuit in both diode test and 200 ohms resistance modes?

two leads together beeps and shows 002 in diode tests

and 0.3 in 200 ohm (no beep)

[sigma7]

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

Q2
Red to Black
Lead 1 to case = inf
case to Lead 1 = inf
Lead 2 to case = inf
case to Lead 2 = inf

These two sets of readings don't agree with each other.

The diode/continuity test says these are a short circuit, and the ohms test says these are an open circuit.

Can you figure out why? I presume the issue is my instructions are ambiguous in some way.

I see the meters from that company do contain fuses, so perhaps the fuse is in the ohms circuit... if you touch the DMM leads together does it show a short circuit in both diode test and 200 ohms resistance modes?

two leads together beeps and shows 002 in diode tests

and 0.3 in 200 ohm (no beep)

Perhaps one of the DMM leads is intermittent? Inspect them for damage, and in diode test mode, while connected together, wiggle and apply tension to all parts of the leads around to see if you can get the reading to change.

[berskyboy]

Q2
Red to Black. (diode test, 200 ohm test)
Lead 1 to case = inf, inf
case to Lead 1 = inf , inf
Lead 2 to case = inf Beep , inf
case to Lead 2 = 4 Beep, inf

case meaning the top of the can?

having a hard time with the measurements

[sigma7]

Q2
Red to Black. (diode test, 200 ohm test)
Lead 1 to case = 3B, inf
case to Lead 1 = 3B , inf

These don't agree... diode test shows short, 200 ohms says not short.... if not the DMM leads, perhaps the rotary switch of the DMM doesn't always make good contact?

[berskyboy]

Today at 06:35:45 PM
Last Edit: Today at 06:45:36 PM by berskyboy
Q2
Red to Black. (diode test, 200 ohm test)
Lead 1 to case = inf, inf
case to Lead 1 = inf , inf
Lead 2 to case = inf Beep , inf
case to Lead 2 = 4 Beep, inf

case meaning the top of the can?

having a hard time with the measurements

[sigma7]

case meaning the top of the can?

Case meaning the silvery part of the transistor, so not the black heatsink (if still attached), not a surface with the thermal grease on it (if any is showing). The case is any part of the silvery domed cylinder and the trapezoid plate with screw holes it is attached to.

Perhaps there is oxidization or corrosion or some other contamination on the surface that you need to scratch through to make good contact.

[berskyboy]

Q2

Red to Black. (diode test, 200 ohm test)
Lead 1 to case = 2 beep, 0.6
case to Lead 1 = 3 beep, 0.6
Lead 2 to case = 3 beep,1.6
case to Lead 2 = inf, inf

[sigma7]

Lead 2 to case = 3 beep,1.6
case to Lead 2 = inf, inf

Again, the lack of symmetry between short and open circuit measurements indicates a measurement problem.

Dunno what to say... keep fiddling with it until you figure out how to get consistent results... it may be the DMM, the leads, poor contact between the probes and the device...

[berskyboy]

Q1

Red to Black. (diode test, 200 ohm test)
Lead 1 to case = inf beep, inf
case to Lead 1 = 2 beep, 0.4
Lead 2 to case = 3 beep,1.2
case to Lead 2 = 2beep, 0.5

[berskyboy]

I can try and buy another DMM, this one might be cheap?

[berskyboy]

Q2

Red to Black. (diode test, 200 ohm test)
Lead 1 to case = 5 beep ,1.2
case to Lead 1 = 6 beep, 1.6
Lead 2 to case = 3 beep ,0.7
case to Lead 2 = 3 beep,1.5

[sigma7]

I can try and buy another DMM, this one might be cheap?

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.)

[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.