Date   

Re: OT!!! OT - WARNING OT! - Spark plug internal resistance -- OT OT OT ...with a later possible tie-in to Tek scopes!

william_b_noble
 

a couple of thoughts - 1) the plug gap seems wide - I don't have any books handy that go that new, but .030 is pretty typical. no, wait, I just found a 1986 Champion master application catalog (#5), and sure enough it has an entry for Ford, 1986 - the 302 V8 uses RE10LC, gap .050, the 351 uses RV12YC, gap .044

hope this helps a bit - I doubt the plugs are your issue, I'd suspect the distributor cap, wires or rotor


Re: OT!!! OT - WARNING OT! - Spark plug internal resistance -- OT OT OT ...with a later possible tie-in to Tek scopes!

Stephen Hanselman
 

Probably a dumb question, but when you set timing was the vacuum advance hose off? Also most of the time I did these things I used 0.014 for the points gap/

Regards,

Stephen Hanselman

On Jul 7, 2019, at 19:33, Leon Robinson <leon-robinson@sbcglobal.net> wrote:

Look at the ignition system in the dark with the engine running,
ANY BLUE GLOW is a problem area.

Leon Robinson K5JLR

Political Correctness is a Political Disease.
Politicians and Diapers should be changed
often and for the same reasons.

On Sunday, July 7, 2019, 8:36:56 PM CDT, Mlynch001 <mlynch002@gmail.com> wrote:

Plug wires should definitely have a measurable difference in resistance, proportional to the length, unless they are solid wire core, which has very little resistance. What type of wires are you running? I would do a compression test as a precaution. Low compression will cause variation in firing voltages at the plugs. NGK plugs typically use a 5K resistor for reduction of Electromagnetic Interference. This was the typical " standard" value that we saw in my 25+ years in the motorcycle business for resistor plugs. I would say that 20K was too much. NGK or ND Resistor plugs were standard in later years, since HONDA insisted on using real copper ignition wires, not resistance wires and the interference from non- resistor plugs caused all kinds of issues with electronics. Your spark energy will definitely vary from cylinder to cylinder, based on the plug resistance, wire resistance, compression and other factors. When we ran a SUN tester, years ago, we allowed 5% +/- from low to high between individual cylinder spark peaks. BTW, Interesting use of the scope!

--
Michael Lynch
Dardanelle, AR





Re: OT!!! OT - WARNING OT! - Spark plug internal resistance -- OT OT OT ...with a later possible tie-in to Tek scopes!

Leon Robinson
 

Look at the ignition system in the dark with the engine running,
ANY BLUE GLOW is a problem area.

Leon Robinson    K5JLR

Political Correctness is a Political Disease.
Politicians and Diapers should be changed
often and for the same reasons.

On Sunday, July 7, 2019, 8:36:56 PM CDT, Mlynch001 <mlynch002@gmail.com> wrote:

Plug wires should definitely have a measurable difference in resistance, proportional to the length, unless they are solid wire core, which has very little resistance.  What type of wires are you running?  I would do a compression test as a precaution.  Low compression will cause variation in firing voltages at the plugs.  NGK plugs typically use a 5K resistor for reduction of Electromagnetic Interference.  This was the typical " standard" value that we saw in my 25+ years in the motorcycle business for resistor plugs.  I would say that 20K was too much.  NGK or ND Resistor plugs were standard in later years, since HONDA insisted on using real copper ignition wires, not resistance wires and the interference from non- resistor plugs caused all kinds of issues with electronics.    Your spark energy will definitely vary from cylinder to cylinder, based on the plug resistance, wire resistance, compression and other factors.  When we ran a SUN tester, years ago, we allowed 5% +/- from low to high between individual cylinder spark peaks.  BTW, Interesting use of the scope!

--
Michael Lynch
Dardanelle, AR


Re: OT!!! OT - WARNING OT! - Spark plug internal resistance -- OT OT OT ...with a later possible tie-in to Tek scopes!

Mlynch001
 

Plug wires should definitely have a measurable difference in resistance, proportional to the length, unless they are solid wire core, which has very little resistance. What type of wires are you running? I would do a compression test as a precaution. Low compression will cause variation in firing voltages at the plugs. NGK plugs typically use a 5K resistor for reduction of Electromagnetic Interference. This was the typical " standard" value that we saw in my 25+ years in the motorcycle business for resistor plugs. I would say that 20K was too much. NGK or ND Resistor plugs were standard in later years, since HONDA insisted on using real copper ignition wires, not resistance wires and the interference from non- resistor plugs caused all kinds of issues with electronics. Your spark energy will definitely vary from cylinder to cylinder, based on the plug resistance, wire resistance, compression and other factors. When we ran a SUN tester, years ago, we allowed 5% +/- from low to high between individual cylinder spark peaks. BTW, Interesting use of the scope!

--
Michael Lynch
Dardanelle, AR


Re: T922 Power Supply Problem

Harvey White
 

OK, then there's several things to think of.

1) with no power on the other boards, and a decent (several K resistance) to ground on the power leads on the boards themselves, I'm not sure what's holding down the power supply lines on the boards.

2) I assume that without any boards plugged in, the main voltages are down.

with the main voltages down, and having replaced *every* capacitor (and <I'll never tell> all the capacitors in the right way), I'll assume that all the resistance readings are decent.  Then the question is:  *what* if shorted, would pull the voltages down.  You can tell if the voltages are down by looking at the current sense resistors (if any), measuring the voltage across them, and then seeing  what the current is from that.  If the current sense resistor is connected between the base and emitter of a transistor, any reading over about .6 to .7 volts indicates that the supply is trying to current limit.

That indicates that something is pulling too much current.  If the supply feeds another one, check that other supply too.

Harvey

On 7/7/2019 8:37 PM, dcane4@gmail.com wrote:
Forgot to mention, I also reflowed the solder on the connectors on the power supply board and interface board.




Re: OT!!! OT - WARNING OT! - Spark plug internal resistance -- OT OT OT ...with a later possible tie-in to Tek scopes!

Reginald Beardsley
 

FWIW I verified the 10 K resistance in the 1968 3rd ed of ""internal Combustion Engines" by Edward F. Obert which is a mechanical engineering textbook


Re: T922 Power Supply Problem

Mlynch001
 

On Sun, Jul 7, 2019 at 07:17 PM, @DC912 wrote:


Thanks Michael.

I removed and tested the transistors out of circuit. All are good.

I also removed the IC, and installed a new replacement IC in a socket. No
change. Same results as above.

Should I test just the 8v circuit on the power supply board out of the scope?
Dave





Dave,

I am certainly not an expert, but if it is possible to operate the LV supply without a load, it would help you to determine if the problem lies with the supply or one of the other boards in that scope. I have restored a couple of T922/935 scopes to operation, but never had any issues with the LV power supply. Have you checked the voltages at the various components in the supply against the schematic? How about VR746? This is a 9.1 Zener that tends to fail quite often. Any of those many diodes failing could cause problems. I have seen several ZENER and other diode failures in older equipment that I have repaired, most recently in my Type 576 Curve tracer. You replaced C738,758,778 along with C722, 742 and 743 ?

--
Michael Lynch
Dardanelle, AR


Re: OT!!! OT - WARNING OT! - Spark plug internal resistance -- OT OT OT ...with a later possible tie-in to Tek scopes!

Daniel Koller
 

Nope.  Was referring only to plug gap.   I don't know what the points gap is.  But it is irrelevant, as my *measured* dwell is about 30 degrees- what it's supposed to be.
  Dan

On Sunday, July 7, 2019, 07:34:08 PM EDT, n7qmm25 <n7qmm25@ykwc.net> wrote:

The distributor points are set at 0.019........ Spark plugs are around
0.032. If you set the distributor points at 0.036 no wonder you have a
rough idle.

On 7/7/2019 3:26 PM, Daniel Koller via Groups.Io wrote:
Hi All,
    Warning!  this is OFF TOPIC.   However,  I am writing here because of the possible connection to the Tek 547 epoxy issue in the HV transformers, and a a Tek tie-in at the end.
    The problem:  I am getting my vintage 1967 Mustang on the road and I have a rough idle.  I am fixing issues in the ignition system and I am replacing the spark plugs. This particular car had the engine replaced in the 1980's with a 1978 vintage 302 (V8).  The spark plugs in it are Motorcraft ASF52.   Because it is a 1978 engine, but with a point-based ignition system, it has been recommended that I re-gap the points to 0.036", which I did.  I am also checking the resistance of the plug wires, AND the plugs themselves as these are "resistor plugs" designed to reduce radio interference.
     The plug wires all have a resistance of about 1 KOhm regardless of length.
     So, the plugs coming OUT of the car are worn, old, well used, and range between 4-8 KOhm resistance.  One of them was an outlier and had 250 Ohms resistance.    There was a fair amount of crud on the central electrode surface that I had to scrape off to make electrical contact, so I don't know what the effective resistance of this film was.
     But I also received a set of NOS (New Old Stock) plugs, in original boxes, fresh from ebay.   I re-gapped these plugs and then measured the resistances.  All of them are about 12.5 KOhm (+/-0.5 K) and one of them is 20 KOhm!  These are the same part number.  What gives!?!?   Did my original plugs start out at ~12 KOhms and wore down with use to where they are now, OR, did the NOS parts start out at 4 KOhm and the resistance ROSE to 12 KOhm sitting on the shelf for 40 years?  I am wondering now if this is not something akin to the epoxy issue in the Tek HV transformers.  These plugs have a "carbon ceramic" based resistor in them.  Is it possible that over 40 years moisture diffused into them and caused the resistance to rise?
....come to think of it, if they are indeed carbon resistors, they *will* rise with age, just like the carbon resistors sitting in the back shelf of the shop, no?  These too take on water over the eons.  Did I just answer my own question?
    For that matter, does anyone know what the resistance value of a resistor spark plug is *supposed to be*?    I browsed all over the interwebs and only found a few anecdotal references to what the plugs should be.  One website said to throw them out if they are over 5K and under 500 Ohms.  That's a big range.  But NOWHERE can I actually find specifications for the resistances of the spark plugs.  That's not even listed in my 1967 Ford shop manual re-print.   I can find every other detail of the plugs, just not the resistance.  The engineer in me really wants to know.   It's driving me nuts that this aspect of a car would be so under-specified.
    Ok, now for the actual Tek tie-in.   What started this is my attempts to figure out why my car would stall when I put it into gear, despite every other aspect of the carburetor and ignition working properly.   It turned out to be the ignition coil.  When it got hot, some time AFTER the engine fully warmed up, the primary resistance rose and the spark was not strong enough to take the extra load.  So in the process of trying to diagnose, I made some capacitive probes and connected them to my trusty 545.  A screen shot is attached (I'll eventually put a good picture up in a photo album, but I think there is enough description here that it's ok if this pic someday gets lost).   I triggered the sweep on cylinder one and displayed all of them in the attached image.  There are multiple traces and it's a bit jittery because the idle was jittery.   Left to right are displayed cylinders 1-5-4-2-6-3-7-8 in that order.   Note that the "firing line" for cylinder #6 is much higher than the others.   This is odd, because that plug read 6.4KOhms, so was NOT one of the higher ones.    The gap was also about the same.  So, is it possible that the surface crud on the electrode really matters?  I guess another possibility is a stuck valve, making this cylinder leaner than the others, which would also raise the firing line.
     Note that the vertical scale is uncalibrated on the 20V/div setting, so in reality it's ~~100-200 V/division.   There's also an ~~10,000:1 capacitive divider in the probe.  The actual plug firing voltages are very narrow peaks, not visible off the top of the CRT. What we are seeing here is the gas discharge during the time the plugs are firing.   The horizontal scale is ~12 mS per division  and the engine is running at ~1000 RPM. (The distributor turns at half the engine RPMs for a 4-stroke cycle).
    Another cool thing I was able to do is switch to delayed triggering, and I was able to use the delaying sweep to "step through" each of the cylinders in sequence, to look at them more carefully.   Unfortunately, due to the rough idle, the engine speed, hence the timing varies, so it's hard to see the trace easily beyond about cylinder 2 (the fourth one in order), much less photograph it.  But I can get a good quick look at them nonetheless.  I'm made myself a nifty ignition analyzer.
     The next steps are to replace the plugs with good ones, and repeat the measurements with a nice stable engine to see what a good firing sequence looks like, and hopefully all cylinders will have similar response with good plugs.  I will also use some chinese-made clip-on probes I picked up on Amazon or e-bay for about $15 each.
    But again, if anyone here has information on the correct spark plug resistance, and in particular, what it should be for a 1967 Mustang with point ignition, PLEASE let me know.
    Thanks,
    Dan




 




Re: OT!!! OT - WARNING OT! - Spark plug internal resistance -- OT OT OT ...with a later possible tie-in to Tek scopes!

Reginald Beardsley
 

I had a look in my 4th ed Bosch "Automotive Handbook" which is an automotive engineering handbook. The voltage available from a breaker ignition system goes down as the engine speed increases because the magnetic field has less time to build up.

I can find nothing about resistance and EMI reduction. Too narrow a gap will make smooth idling impossible, but 0.036 doesn't strike me as too narrow. Gaps typically range from 0.030 to 0.060.

Resistive paths in parallel with the gap will dramatically reduce the available spark voltage. A 500 K resistance will very nearly make it impossible to run the engine. A 1 M resistance will cut the available secondary voltage roughly in half. It doesn't take a lot of crud to create that level of resistance.

Using a wire brush to clean a spark plug is generally a bad idea as it can leave a metal film on the insulator. though I had success doing that on badly carbon fouled plugs back when I drove high mileage air cooled VWs.

Having struck out on the Bosch handbook which is incredibly good, I looked for another reference.

According to"Modern Automotive Technology" by James E. Duffy, resistance plug wires have a resistance of 10 K per foot. Resistor plugs also have a 10 K internal resistance. This is a 1994 trade school text. By the time I bought it, I'd already rebuilt a 1967 VW bus engine in a truck stop parking lot after losing a valve stem and driven 90 miles back home on 3 cylinders when a wad of blank shop tickets in the fan of a Ghia melted a hole in #3. I pulled the rocker arm, removed the pushrods for #3 and went on my way. I bought it because it was very thorough. I don't recall that I ever used it for anything before, but I think finding the answer to the plug and wire resistance question confirms it was a smart addition to my library.

I'd appreciate details of your test probe. I'd like to make one for myself.


Re: T922 Power Supply Problem

@DC912
 

Forgot to mention, I also reflowed the solder on the connectors on the power supply board and interface board.


Re: T922 Power Supply Problem

@DC912
 

Thanks Harvey. I replaced all of the electrolytics on the power supply board for safe measure, although they all tested okay. I also checked all of the electrolytics on the other boards, and the one tantalum I saw. None were shorted and they all test okay for capacitance and esr on my LCR meter. I’m stumped, but would really like to get this scope back in working order. Dave


Re: T922 Power Supply Problem

@DC912
 

Thanks Michael.

I removed and tested the transistors out of circuit. All are good.

I also removed the IC, and installed a new replacement IC in a socket. No change. Same results as above.

Should I test just the 8v circuit on the power supply board out of the scope?
Dave


Re: T922 Power Supply Problem

Harvey White
 

One immediate suggestion would be to check the capacitors on the 8 and -8 volt bulk supplies, then check the capacitors in the supplies that the -8 and 8 feed.

That you have several K ohms on the other boards to ground suggests that they're ok.

Harvey

On 7/7/2019 2:58 PM, Mlynch001 wrote:
On Sun, Jul 7, 2019 at 01:37 PM, @DC912 wrote:

Hello.

With power on, the power lamp does not light or blink.

I measure negative 700mv at the -8 test point on the power supply board.

I measure positive 700mv at the +8 test point on the power supply board,

The secondary on the power transformer for the 8v supply tests good.

I measure 82 volts at the +100v test point on the power supply board.

With the power supply board in the scope, resistance between -8v test point
and ground is 180 ohms, 200 ohms between the +8v test point and ground.

With the power supply board removed from the scope, resistance between the -8v
test point and ground is 35k ohms, 20k ohms between the +8v and ground.

I also removed the vertical and horizontal boards to check the resistances on
the 8v and -8v rails to ground on those boards. None of the rails on the two
boards measured lower than several kohms.

Any suggestions on where to go from here would be greatly appreciated.

Thanks. Dave.
I would check the items listed in the service manual under Service Information. U742 is part of both +8 and -8 power supplies. Service manual also mentions several other transistors. -8V check Q772-774-776 +8V Check Q752-754-756.


Re: OT!!! OT - WARNING OT! - Spark plug internal resistance -- OT OT OT ...with a later possible tie-in to Tek scopes!

n7qmm25
 

The distributor points are set at 0.019........ Spark plugs are around 0.032. If you set the distributor points at 0.036 no wonder you have a rough idle.

On 7/7/2019 3:26 PM, Daniel Koller via Groups.Io wrote:
Hi All,
  Warning!  this is OFF TOPIC.   However,  I am writing here because of the possible connection to the Tek 547 epoxy issue in the HV transformers, and a a Tek tie-in at the end.
  The problem:  I am getting my vintage 1967 Mustang on the road and I have a rough idle.  I am fixing issues in the ignition system and I am replacing the spark plugs. This particular car had the engine replaced in the 1980's with a 1978 vintage 302 (V8).  The spark plugs in it are Motorcraft ASF52.   Because it is a 1978 engine, but with a point-based ignition system, it has been recommended that I re-gap the points to 0.036", which I did.  I am also checking the resistance of the plug wires, AND the plugs themselves as these are "resistor plugs" designed to reduce radio interference.
   The plug wires all have a resistance of about 1 KOhm regardless of length.
   So, the plugs coming OUT of the car are worn, old, well used, and range between 4-8 KOhm resistance.  One of them was an outlier and had 250 Ohms resistance.    There was a fair amount of crud on the central electrode surface that I had to scrape off to make electrical contact, so I don't know what the effective resistance of this film was.
   But I also received a set of NOS (New Old Stock) plugs, in original boxes, fresh from ebay.   I re-gapped these plugs and then measured the resistances.  All of them are about 12.5 KOhm (+/-0.5 K) and one of them is 20 KOhm!  These are the same part number.  What gives!?!?   Did my original plugs start out at ~12 KOhms and wore down with use to where they are now, OR, did the NOS parts start out at 4 KOhm and the resistance ROSE to 12 KOhm sitting on the shelf for 40 years?  I am wondering now if this is not something akin to the epoxy issue in the Tek HV transformers.  These plugs have a "carbon ceramic" based resistor in them.  Is it possible that over 40 years moisture diffused into them and caused the resistance to rise?
....come to think of it, if they are indeed carbon resistors, they *will* rise with age, just like the carbon resistors sitting in the back shelf of the shop, no?  These too take on water over the eons.  Did I just answer my own question?
  For that matter, does anyone know what the resistance value of a resistor spark plug is *supposed to be*?    I browsed all over the interwebs and only found a few anecdotal references to what the plugs should be.  One website said to throw them out if they are over 5K and under 500 Ohms.  That's a big range.  But NOWHERE can I actually find specifications for the resistances of the spark plugs.  That's not even listed in my 1967 Ford shop manual re-print.   I can find every other detail of the plugs, just not the resistance.  The engineer in me really wants to know.   It's driving me nuts that this aspect of a car would be so under-specified.
  Ok, now for the actual Tek tie-in.   What started this is my attempts to figure out why my car would stall when I put it into gear, despite every other aspect of the carburetor and ignition working properly.   It turned out to be the ignition coil.  When it got hot, some time AFTER the engine fully warmed up, the primary resistance rose and the spark was not strong enough to take the extra load.  So in the process of trying to diagnose, I made some capacitive probes and connected them to my trusty 545.  A screen shot is attached (I'll eventually put a good picture up in a photo album, but I think there is enough description here that it's ok if this pic someday gets lost).   I triggered the sweep on cylinder one and displayed all of them in the attached image.  There are multiple traces and it's a bit jittery because the idle was jittery.   Left to right are displayed cylinders 1-5-4-2-6-3-7-8 in that order.   Note that the "firing line" for cylinder #6 is much higher than the others.   This is odd, because that plug read 6.4KOhms, so was NOT one of the higher ones.    The gap was also about the same.  So, is it possible that the surface crud on the electrode really matters?  I guess another possibility is a stuck valve, making this cylinder leaner than the others, which would also raise the firing line.
   Note that the vertical scale is uncalibrated on the 20V/div setting, so in reality it's ~~100-200 V/division.   There's also an ~~10,000:1 capacitive divider in the probe.  The actual plug firing voltages are very narrow peaks, not visible off the top of the CRT. What we are seeing here is the gas discharge during the time the plugs are firing.   The horizontal scale is ~12 mS per division  and the engine is running at ~1000 RPM. (The distributor turns at half the engine RPMs for a 4-stroke cycle).
  Another cool thing I was able to do is switch to delayed triggering, and I was able to use the delaying sweep to "step through" each of the cylinders in sequence, to look at them more carefully.   Unfortunately, due to the rough idle, the engine speed, hence the timing varies, so it's hard to see the trace easily beyond about cylinder 2 (the fourth one in order), much less photograph it.  But I can get a good quick look at them nonetheless.  I'm made myself a nifty ignition analyzer.
   The next steps are to replace the plugs with good ones, and repeat the measurements with a nice stable engine to see what a good firing sequence looks like, and hopefully all cylinders will have similar response with good plugs.  I will also use some chinese-made clip-on probes I picked up on Amazon or e-bay for about $15 each.
  But again, if anyone here has information on the correct spark plug resistance, and in particular, what it should be for a 1967 Mustang with point ignition, PLEASE let me know.
  Thanks,
  Dan







Re: OT!!! OT - WARNING OT! - Spark plug internal resistance -- OT OT OT ...with a later possible tie-in to Tek scopes!

Daniel Koller
 

Hi folks,

  The photo I took is here:

https://groups.io/g/TekScopes/photo/92873/0?p=Created,,,20,2,0,0



  Dan

On Sunday, July 7, 2019, 06:27:51 PM EDT, Daniel Koller via Groups.Io <kaboomdk=yahoo.com@groups.io> wrote:





Hi All,
  Warning!  this is OFF TOPIC.   However,  I am writing here because of the possible connection to the Tek 547 epoxy issue in the HV transformers, and a a Tek tie-in at the end.
  The problem:  I am getting my vintage 1967 Mustang on the road and I have a rough idle.  I am fixing issues in the ignition system and I am replacing the spark plugs. This particular car had the engine replaced in the 1980's with a 1978 vintage 302 (V8).  The spark plugs in it are Motorcraft ASF52.   Because it is a 1978 engine, but with a point-based ignition system, it has been recommended that I re-gap the points to 0.036", which I did.  I am also checking the resistance of the plug wires, AND the plugs themselves as these are "resistor plugs" designed to reduce radio interference.  
   The plug wires all have a resistance of about 1 KOhm regardless of length. 
   So, the plugs coming OUT of the car are worn, old, well used, and range between 4-8 KOhm resistance.  One of them was an outlier and had 250 Ohms resistance.    There was a fair amount of crud on the central electrode surface that I had to scrape off to make electrical contact, so I don't know what the effective resistance of this film was.
   But I also received a set of NOS (New Old Stock) plugs, in original boxes, fresh from ebay.   I re-gapped these plugs and then measured the resistances.  All of them are about 12.5 KOhm (+/-0.5 K) and one of them is 20 KOhm!  These are the same part number.  What gives!?!?   Did my original plugs start out at ~12 KOhms and wore down with use to where they are now, OR, did the NOS parts start out at 4 KOhm and the resistance ROSE to 12 KOhm sitting on the shelf for 40 years?  I am wondering now if this is not something akin to the epoxy issue in the Tek HV transformers.  These plugs have a "carbon ceramic" based resistor in them.  Is it possible that over 40 years moisture diffused into them and caused the resistance to rise?
....come to think of it, if they are indeed carbon resistors, they *will* rise with age, just like the carbon resistors sitting in the back shelf of the shop, no?  These too take on water over the eons.  Did I just answer my own question?
  For that matter, does anyone know what the resistance value of a resistor spark plug is *supposed to be*?    I browsed all over the interwebs and only found a few anecdotal references to what the plugs should be.  One website said to throw them out if they are over 5K and under 500 Ohms.  That's a big range.  But NOWHERE can I actually find specifications for the resistances of the spark plugs.  That's not even listed in my 1967 Ford shop manual re-print.   I can find every other detail of the plugs, just not the resistance.  The engineer in me really wants to know.   It's driving me nuts that this aspect of a car would be so under-specified.
  Ok, now for the actual Tek tie-in.   What started this is my attempts to figure out why my car would stall when I put it into gear, despite every other aspect of the carburetor and ignition working properly.   It turned out to be the ignition coil.  When it got hot, some time AFTER the engine fully warmed up, the primary resistance rose and the spark was not strong enough to take the extra load.  So in the process of trying to diagnose, I made some capacitive probes and connected them to my trusty 545.  A screen shot is attached (I'll eventually put a good picture up in a photo album, but I think there is enough description here that it's ok if this pic someday gets lost).   I triggered the sweep on cylinder one and displayed all of them in the attached image.  There are multiple traces and it's a bit jittery because the idle was jittery.   Left to right are displayed cylinders 1-5-4-2-6-3-7-8 in that order.   Note that the "firing line" for cylinder #6 is much higher than the others.   This is odd, because that plug read 6.4KOhms, so was NOT one of the higher ones.    The gap was also about the same.  So, is it possible that the surface crud on the electrode really matters?  I guess another possibility is a stuck valve, making this cylinder leaner than the others, which would also raise the firing line.
   Note that the vertical scale is uncalibrated on the 20V/div setting, so in reality it's ~~100-200 V/division.   There's also an ~~10,000:1 capacitive divider in the probe.  The actual plug firing voltages are very narrow peaks, not visible off the top of the CRT. What we are seeing here is the gas discharge during the time the plugs are firing.   The horizontal scale is ~12 mS per division  and the engine is running at ~1000 RPM. (The distributor turns at half the engine RPMs for a 4-stroke cycle).
  Another cool thing I was able to do is switch to delayed triggering, and I was able to use the delaying sweep to "step through" each of the cylinders in sequence, to look at them more carefully.   Unfortunately, due to the rough idle, the engine speed, hence the timing varies, so it's hard to see the trace easily beyond about cylinder 2 (the fourth one in order), much less photograph it.  But I can get a good quick look at them nonetheless.  I'm made myself a nifty ignition analyzer.  
   The next steps are to replace the plugs with good ones, and repeat the measurements with a nice stable engine to see what a good firing sequence looks like, and hopefully all cylinders will have similar response with good plugs.  I will also use some chinese-made clip-on probes I picked up on Amazon or e-bay for about $15 each.     
  But again, if anyone here has information on the correct spark plug resistance, and in particular, what it should be for a 1967 Mustang with point ignition, PLEASE let me know.    
  Thanks, 
  Dan


OT!!! OT - WARNING OT! - Spark plug internal resistance -- OT OT OT ...with a later possible tie-in to Tek scopes!

Daniel Koller
 

Hi All,
  Warning!  this is OFF TOPIC.   However,  I am writing here because of the possible connection to the Tek 547 epoxy issue in the HV transformers, and a a Tek tie-in at the end.
  The problem:  I am getting my vintage 1967 Mustang on the road and I have a rough idle.  I am fixing issues in the ignition system and I am replacing the spark plugs. This particular car had the engine replaced in the 1980's with a 1978 vintage 302 (V8).  The spark plugs in it are Motorcraft ASF52.   Because it is a 1978 engine, but with a point-based ignition system, it has been recommended that I re-gap the points to 0.036", which I did.  I am also checking the resistance of the plug wires, AND the plugs themselves as these are "resistor plugs" designed to reduce radio interference.  
   The plug wires all have a resistance of about 1 KOhm regardless of length. 
   So, the plugs coming OUT of the car are worn, old, well used, and range between 4-8 KOhm resistance.  One of them was an outlier and had 250 Ohms resistance.    There was a fair amount of crud on the central electrode surface that I had to scrape off to make electrical contact, so I don't know what the effective resistance of this film was.
   But I also received a set of NOS (New Old Stock) plugs, in original boxes, fresh from ebay.   I re-gapped these plugs and then measured the resistances.  All of them are about 12.5 KOhm (+/-0.5 K) and one of them is 20 KOhm!  These are the same part number.  What gives!?!?   Did my original plugs start out at ~12 KOhms and wore down with use to where they are now, OR, did the NOS parts start out at 4 KOhm and the resistance ROSE to 12 KOhm sitting on the shelf for 40 years?  I am wondering now if this is not something akin to the epoxy issue in the Tek HV transformers.  These plugs have a "carbon ceramic" based resistor in them.  Is it possible that over 40 years moisture diffused into them and caused the resistance to rise?
....come to think of it, if they are indeed carbon resistors, they *will* rise with age, just like the carbon resistors sitting in the back shelf of the shop, no?  These too take on water over the eons.  Did I just answer my own question?
  For that matter, does anyone know what the resistance value of a resistor spark plug is *supposed to be*?    I browsed all over the interwebs and only found a few anecdotal references to what the plugs should be.  One website said to throw them out if they are over 5K and under 500 Ohms.  That's a big range.  But NOWHERE can I actually find specifications for the resistances of the spark plugs.  That's not even listed in my 1967 Ford shop manual re-print.   I can find every other detail of the plugs, just not the resistance.  The engineer in me really wants to know.   It's driving me nuts that this aspect of a car would be so under-specified.
  Ok, now for the actual Tek tie-in.   What started this is my attempts to figure out why my car would stall when I put it into gear, despite every other aspect of the carburetor and ignition working properly.   It turned out to be the ignition coil.  When it got hot, some time AFTER the engine fully warmed up, the primary resistance rose and the spark was not strong enough to take the extra load.  So in the process of trying to diagnose, I made some capacitive probes and connected them to my trusty 545.  A screen shot is attached (I'll eventually put a good picture up in a photo album, but I think there is enough description here that it's ok if this pic someday gets lost).   I triggered the sweep on cylinder one and displayed all of them in the attached image.  There are multiple traces and it's a bit jittery because the idle was jittery.   Left to right are displayed cylinders 1-5-4-2-6-3-7-8 in that order.   Note that the "firing line" for cylinder #6 is much higher than the others.   This is odd, because that plug read 6.4KOhms, so was NOT one of the higher ones.    The gap was also about the same.  So, is it possible that the surface crud on the electrode really matters?  I guess another possibility is a stuck valve, making this cylinder leaner than the others, which would also raise the firing line.
   Note that the vertical scale is uncalibrated on the 20V/div setting, so in reality it's ~~100-200 V/division.   There's also an ~~10,000:1 capacitive divider in the probe.  The actual plug firing voltages are very narrow peaks, not visible off the top of the CRT. What we are seeing here is the gas discharge during the time the plugs are firing.   The horizontal scale is ~12 mS per division  and the engine is running at ~1000 RPM. (The distributor turns at half the engine RPMs for a 4-stroke cycle).
  Another cool thing I was able to do is switch to delayed triggering, and I was able to use the delaying sweep to "step through" each of the cylinders in sequence, to look at them more carefully.   Unfortunately, due to the rough idle, the engine speed, hence the timing varies, so it's hard to see the trace easily beyond about cylinder 2 (the fourth one in order), much less photograph it.  But I can get a good quick look at them nonetheless.  I'm made myself a nifty ignition analyzer.  
   The next steps are to replace the plugs with good ones, and repeat the measurements with a nice stable engine to see what a good firing sequence looks like, and hopefully all cylinders will have similar response with good plugs.  I will also use some chinese-made clip-on probes I picked up on Amazon or e-bay for about $15 each.     
  But again, if anyone here has information on the correct spark plug resistance, and in particular, what it should be for a 1967 Mustang with point ignition, PLEASE let me know.    
  Thanks, 
  Dan


Re: 2445 CH2 Amplitude is 1/3 of expected value

Chuck Harris <cfharris@...>
 

Probes die new in the box. Don't let appearance do the diagnosis.
Try the probe on the other inputs. If it doesn't work everywhere,
try disassembling it into modules, and reassembling the modules...

The ringing on the leading and trailing edges of the square wave
indicates a mismatch somewhere... like a blown attenuator.

It is extremely popular for new scope users to blow out the input
attenuator on an oscilloscope. They do things like hook them up
to TV flyback circuits, transmitters, or HV circuitry.

Probably the second most popular thing to do (in the never ending
search for things to look at), is to connect the ground clip on the
probe to the hot side of the power line, and burn up the ground clip,
the probe shield, and the green/yellow bonding ground wire inside of
the scope...

- Chuck Harris

Jay H. via Groups.Io wrote:

Hi,

I'm new here and appreciate any advice or direction you can give.

I've acquired a 2445 in excellent cosmetic condition and am at "Amplitude Check" only to find that CH2 is reduced by a factor of 3. It reads 133mV, versus CH1 properly reading the calibrated square wave as 400mV. I've tried DC Leveling and Automated Diagnostics. That multiple of three reminds me of an op-amp.

Also both the start (400 mV) and end (0 mV) of the square wave have a small, leading sine wave imposed over it. I've assumed that it's just a failing lead, but the lead is new (from an unopened package) and now I'm starting to wonder.

I have photos and will try to upload them. But I'm new here and appreciate any guidance.


Re: 2445 CH2 Amplitude off by a factor of 3

Chuck Harris <cfharris@...>
 

It is probably one of four things:

0) A bad probe... check to see if the problem follows the probe.
1) corrosion on the BNC female pin... a little deoxit will help.
2) a burned out attenuator... replacement is usually the only fix.
3) a burned out preamplifier... replacement is usually the only fix.

The attenuator and preamplifier (hybrid) are fairly easy to fix,
but do require a complete recalibration afterwards.

If the signal is right at other positions of the attenuator, then
the problem is the attenuator.

If the signal is wrong at any setting of the attenuator, then it is
likely the BNC pin, or the preamp.

A great place to start is to download a copy of the manual from
BAMA, or Didier's website.

-Chuck Harris

Jay H. via Groups.Io wrote:

Hi,
Thanks in advance for your input.
I just received a barely used 2445; it even came with a probe still in the original, unopened package! It smells new in a 1960's plastic sort of way.
Walking through the "Steps and Adjustments - Amplitude Check", I have found that CH2 displays the calibration waveform with an amplitude of 133mV versus CH1 which properly shows 400mV.
Digging around has left me wondering where to begin. A simple DC Balance (twice now) makes no difference. And that multiple of 3 nags at the back of my mind, like dejavu.
If you have a moment to share your thought, I'd be grateful.
Cheers,
Jay




2445 CH2 Amplitude off by a factor of 3

jcholsap@...
 

Hi,
Thanks in advance for your input.
I just received a barely used 2445; it even came with a probe still in the original, unopened package! It smells new in a 1960's plastic sort of way.
Walking through the "Steps and Adjustments - Amplitude Check", I have found that CH2 displays the calibration waveform with an amplitude of 133mV versus CH1 which properly shows 400mV.
Digging around has left me wondering where to begin. A simple DC Balance (twice now) makes no difference. And that multiple of 3 nags at the back of my mind, like dejavu.
If you have a moment to share your thought, I'd be grateful.
Cheers,
Jay


2445 CH2 Amplitude is 1/3 of expected value

Jay H. <jcholsap@...>
 

Hi,

I'm new here and appreciate any advice or direction you can give.

I've acquired a 2445 in excellent cosmetic condition and am at "Amplitude Check" only to find that CH2 is reduced by a factor of 3. It reads 133mV, versus CH1 properly reading the calibrated square wave as 400mV. I've tried DC Leveling and Automated Diagnostics. That multiple of three reminds me of an op-amp.

Also both the start (400 mV) and end (0 mV) of the square wave have a small, leading sine wave imposed over it. I've assumed that it's just a failing lead, but the lead is new (from an unopened package) and now I'm starting to wonder.

I have photos and will try to upload them. But I'm new here and appreciate any guidance.

--
Jay H.

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