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8116A Code 42

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MarkL:
Analyzing this a little more closely, I want to correct something I said:

--- Quote from: MarkL on February 01, 2024, 04:14:56 pm ---...
And looking at the unit's final output, clearly it's stuck above 0V when the waveform should be more or less symmetric around 0V.  So something is wrongly dragging the output high.  Q502 is one of the intermediate drivers trying to pull the output low, so it's not a surprise it's hot.  It's probably fighting against something that's keeping the output high.
...

--- End quote ---
First, we've determined Q501 and Q502 just run hot, when comparing to a working unit.  So the elevated temperature of Q502 may not be a useful clue.

Second, I was not taking into account the inverting stage in this amplifier (which happens at Q505 and Q506).  So, when the collector of Q501 goes high, the output is forced low.  Therefore, the collector of Q501 might actually be doing the right thing by being pinned high, as instructed by the feedback.  It could be trying to correct for whatever is dragging the output high.

I'd like to add Q507 to the list of measurements.  It sits conveniently between the inverting gain stage (Q503/Q505 and Q504/Q506) and the output driver (emitter follower) stage consisting of Q508/Q510/Q512 and Q509/Q511/Q513.  It may at least help divide the schematic in half for your troubleshooting focus.

Let's also take a look at voltages around Q508 and Q509, since that's where you had to replace them and their associated collector resistors (R559 and R560).  Maybe there's something else dead in the output driver section that you didn't catch.

Note that Q510/Q512 are essentially in parallel with each other, as is the pair Q511/Q513.  They should be sharing currently equally and a quick check should show the emitters in each pair to be at the same voltage, within a mV or so.

I should have some time later today to update my diagram with measurements for these nodes and will repost.

Mick B:
I didn't read the above post yet. I'll be Back.

2/9/24

Hello again Mark, these are the newest measurements. Your schematic idea is brilliant. I was going to edit yours, but I have Adobe Acrobat Pro X, and it doesn’t have the fonts (LibreOffice) has.
I’m having a major issue with my Saab someone stole the ECU. And now I have to learn how to work a Tech 2 Scanner, and the software it uses THAT ONLY WORKS IN XP! Had to bone up on VMware. The updates need to be downloaded (I don’t think XP will access the internet, so I must find the files on the internet and figure out how to get them to load in the software in XP. You can just buy an ECM and reprogram it USING your OLD ECM. See the problem?
 This part is supper complicated, and I’ve only scratched the surface. 
The ECM must be married to the ECM apparently through the security system I have been reading into all hours of the night. For the moment until a few more hours are added into the day is it OK if I forgo the schematic until I get caught up and just post the results.

I used the settings & Gnd. locations noted.

+24v:    +24.0140
-24v:     -24.0123
+15v:    +15.0319
-15v:     -15.0273

U501.7: +14.04263

Q501:    E +066.501mv     B +0.6592v     C +023.8454v
Q502:    E -069.3mv          B -0.7245v     C -08.868v NOTE: these are fluctuating up & down.

R518.R519:  -016.9463mv

CR501:   A +0.65984v      C -035.46mv
CR502:   A -0.2474v         C -034.67mv

U501 . 6:  +013.5805v NOTE: yours is neg.
Q514

Q515: E +012.8370v NOTE: yours is neg.

U502. 6:   -21.2336mv NOTE: yours is pos., and this starts out at -100 and drops to 21. And then starts climbing.

VR501:   A +023.1866v     C +023.9821v
VR502:   A -021.3346        C -08.8716v

Q503:   E +02.23366v       B +23.9812v       C +02.6464v
Q504:   E -020.5156v        B -021.2258v      C -023.6773v

Tempts FREAKEN HOT!! Using UNI-T:  uti260B
U33:  78c
U37:  80c
Q501:  32c
Q502:  53c
R530,31,32:   76c
U401:  74.5c

NOTE: a lot of the voltages were fluctuating,
I also tried jumping R516 w/10K no changes,
Removed Q501 Using a small transistor tester, it tests good. This a 2N2369A
I have NOS   Q501 and 2 transistors coming- it couldn’t hurt.
Thanks Mark

MarkL:
Attached is the schematic with added measurements on the output driver side.  If it would be helpful, I can post the LibreOffice Draw file instead of the PDF.  I can also use a different font if it's picking some weird substitute font.

Let me take a look at your latest measurements and I'll post back.  The pinned output on U501 immediately stands out.  As long as you have waveforms off, I don't see how anything should be fluctuating.

Are you referring to the U33 and U37 on the A3 board where the processor sits, or on the A2 control board?  HP duplicated the U designations on these two boards (how nice of them).  I was referring to the A2 board in my previous post about them being ECL.  But in either case, your U33 and U37 are still too hot, ECL or not.  At the moment I don't think it has anything to do with the distorted output, but it's certainly is something to keep in mind.  Let's focus on the output amp for now and come back to that.


Good luck with your ECM.  I experienced a similar thing with the module security code stuff trying to fix my Toyota Prius about 15 years ago.  After many, many wasted hours, I finally got it to work only to find out the problem was something internal to the motor generator in the engine anyway.  I just take my cars to the dealer now.  I don't give up easily, but they win.

MarkL:
And to answer your question about forgoing the schematic, feel free to use text if that's easier.  I put the measurements in the schematic because it's easier to visualize what's going on, but don't let fancy delivery be an impediment to getting the data out there.

MarkL:
Ok, based on your latest measurements there's some issues with and around Q503.

Note that the Q503 B-E junction is nowhere near 0.7V, and the collector should be around +23.3V or more.  It should be +24V - one diode drop from CR503, or R533 could pull the collector voltage even closer to +24V.

So, Q503 appears dead (open B-E junction, >0.7V), CR503 is also dead (open, >0.7V forward voltage, A to C), and R533 too (open, since at those voltages it would be dissipating about 23W and glowing).

I would double check your voltage readings on Q503, and if confirmed pull it out and verify it out of circuit, as well as CR503 and R533.

When double checking voltages, I would also make sure you can see the +24V rail on the upper side of R533 and the anode of CR503.  It's not beyond possibility that there's a fried trace.

If Q503 is indeed bad, it also wouldn't be a bad idea to check R534 and Q505.  The current that killed it had to go somewhere.

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