LisaList2

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.

Quote from: sigma7 on September 18, 2026, 05:08:49 PMOnce 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

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

Quote from: sigma7 on September 18, 2026, 04:51:46 PMAB 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

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

Quote from: sigma7 on September 18, 2026, 04:35:39 PMSo 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

Quote from: berskyboy on September 18, 2026, 04:17:38 PMwith 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.

Quote from: dmac1267 on September 18, 2026, 03:28:32 AMI am using LisaEm 1.2.7

Since Ray (the LisaEm original author) died, development has moved to
https://github.com/arcanebyte/lisaem ; It is 161 commits ahead of what you are using, so you are missing a lot of good stuff.

Quote from: sigma7 on September 18, 2026, 04:13:20 PMThe 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

Quote from: berskyboy on September 18, 2026, 04:10:09 PM

Quote from: sigma7 on September 18, 2026, 03:54:44 PMIf 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.