Heathkit Engine Ignition Analyser annoying fault! - UK Vintage Radio Repair and Restoration Discussion Forum

mole42uk · 18th May 2014, 12:43 pm

Hi,

I have a Heathkit CO-1015 engine analyser which I built from an old un-assembled kit a couple of years ago. I replaced all the resistors with new film ones and cleaned all the solder areas before assembling it.

Once built, it worked properly for a short time (a few minutes) and then the timebase stopped. It hasn't worked since and now I'm tearing my hair out trying to find the fault. It doesn't help that I can't find the assembly manual that came with the kit, so all I have is the circuit diagram. All the other functions seem to work as they should, but the CRT shows only a vertically oriented line which should be a nice sine wave display if the timebase worked. Both the timebase and the calibration signal for the Y axis are derived from the 50Hz mains.

Has anyone any knowledge of this device, or better yet a copy of the manual that I could borrow?

Richard

Bazz4CQJ · 18th May 2014, 5:01 pm

I'm not familiar with this device, but I wonder whether it is similar to the old analyser made by Hawk? That device actually measured the amount of hydrogen in the gas, but the amount of CO present is in direct proportion, so the meter scale is calibrated in units of CO.

The problem is that such devices pre-date catalytic convertors and don't work on cars with cats.

Anthony Thomas · 18th May 2014, 5:51 pm

Bazz I think Richard is refering to the test oscilloscope by Heathkit not the exhaust gas analyser instrument.

Tony

mole42uk · 19th May 2014, 7:07 am

Hi, Tony is correct - it's an ignition analyser, not a CO analyser.

I have a Sun CO analyser, and my car does not have a CAT!!

Richard

Station X · 19th May 2014, 9:31 am

The circuit is here (yes I know you have it).

http://www.vintage-radio.info/heathkit

Looking at the circuit, the horizontal deflection plates are driven by Q702 and Q703 which have a 250V DC supply. Test voltages are given, so it would be worth checking them.

If you have access to a scope you could check for a saw tooth? driving these transistors.

mole42uk · 19th May 2014, 10:37 am

Hi Graham,

The 250V is probably okay - I can move the spot fully left to right using the Horiz. Position control, and the vertical amp (also driven by the 250V line) is working just fine.

There is no sawtooth driving the transistors. That's what I'm finding a real problem because it seems to be derived from the AC sine wave by Q610 and fed through SW1 to Q304 when SW1 is in the 'Calibrate' position. I can see a square wave at the base of Q601, but it has no signal on the collector. Q601 tests good and has also been substituted as a belt-n-braces approach.

I am going to try and inject a suitable 50Hz signal into the base of Q702, the Horiz output transistor, make sure that moves the spot as I expect, then move back from there.

I have to do some paid work for an hour or two first though :-(

Richard

dave cox · 19th May 2014, 11:42 am

What's the voltage on Q601 collector?
Do you see a signal on Q601 collector when its NOT in the CAL position?

Working back the other way, Q701 is a level shifter. Does it show sensible voltages ?

dc

cmjones01 · 19th May 2014, 12:19 pm

If there's no signal on Q601 collector, what about the resistor R604 from its collector to the positive supply? If that was open-circuit it could cause this problem.

Chris

mole42uk · 19th May 2014, 1:45 pm

Q601 collector has about 34mV DC which is in accordance with the circuit.

There is a signal on Q601 collector when SW1 is NOT in CAL position. The signal is a 40mV p-p pulse alternately pos and neg at about 50Hz. It disappears as soon as the switch is put into CAL, but when the switch is in anything other than CAL the collector isn't connected to anything except the 100k resistor (R604)

Q701 was not showing anything sensible at all and testing the transistor out of circuit suggested it wasn't happy. I changed that but still no luck.

Applying a 600mV 50Hz sine wave to the base of Q702 makes the trace move side-to side in the expected manner. Putting a similar signal to the base of Q701 does not make the trace move, yet I cannot find a fault with Q701, or the zener or the 4k7 resistor.

Richard

dave cox · 19th May 2014, 3:25 pm

The zener (Q701 emitter) needs to be reverse biased into breakdown. You need to provide enough bias voltage to do this (Q701 base) with the sweep superimposed on top. If I'm reading it right, it will need LESS than14.4V less the zener voltage then less a bit more (your 600mV) to get Q701 into its operating region.

Next back in the chain is the FET follower then the ramp integrator, around C401 (?) and current source Q402.

dc

mole42uk · 20th May 2014, 10:18 am

Thanks to everyone who's helped so far. I still haven't made any improvement and after nearly two solid days I have to put the covers back on and take a break!

I'll be into it again when my head has recovered!

Richard

18th May 2014, 12:43 pm	#1
mole42uk Nonode Join Date: Aug 2010 Location: Resolven, Wales; and Bristol, England Posts: 2,613	Heathkit Engine Ignition Analyser annoying fault! Hi, I have a Heathkit CO-1015 engine analyser which I built from an old un-assembled kit a couple of years ago. I replaced all the resistors with new film ones and cleaned all the solder areas before assembling it. Once built, it worked properly for a short time (a few minutes) and then the timebase stopped. It hasn't worked since and now I'm tearing my hair out trying to find the fault. It doesn't help that I can't find the assembly manual that came with the kit, so all I have is the circuit diagram. All the other functions seem to work as they should, but the CRT shows only a vertically oriented line which should be a nice sine wave display if the timebase worked. Both the timebase and the calibration signal for the Y axis are derived from the 50Hz mains. Has anyone any knowledge of this device, or better yet a copy of the manual that I could borrow? Richard

18th May 2014, 5:01 pm	#2
Bazz4CQJ Dekatron Join Date: Apr 2009 Location: Oxfordshire, UK. Posts: 4,935	Re: Heathkit Engine Analyser annoying fault! I'm not familiar with this device, but I wonder whether it is similar to the old analyser made by Hawk? That device actually measured the amount of hydrogen in the gas, but the amount of CO present is in direct proportion, so the meter scale is calibrated in units of CO. The problem is that such devices pre-date catalytic convertors and don't work on cars with cats.

18th May 2014, 5:51 pm	#3
Anthony Thomas Hexode Join Date: Jan 2013 Location: Ålesund, Norway Posts: 361	Re: Heathkit Engine Analyser annoying fault! Bazz I think Richard is refering to the test oscilloscope by Heathkit not the exhaust gas analyser instrument. Tony

19th May 2014, 7:07 am	#4
mole42uk Nonode Join Date: Aug 2010 Location: Resolven, Wales; and Bristol, England Posts: 2,613	Re: Heathkit Engine Analyser annoying fault! Hi, Tony is correct - it's an ignition analyser, not a CO analyser. I have a Sun CO analyser, and my car does not have a CAT!! Richard

19th May 2014, 9:31 am	#5
Station X Moderator Join Date: Jan 2003 Location: Ipswich, Suffolk, IP4, UK. Posts: 21,289	Re: Heathkit Engine Analyser annoying fault! The circuit is here (yes I know you have it). http://www.vintage-radio.info/heathkit Looking at the circuit, the horizontal deflection plates are driven by Q702 and Q703 which have a 250V DC supply. Test voltages are given, so it would be worth checking them. If you have access to a scope you could check for a saw tooth? driving these transistors. __________________ Graham. Forum Moderator Reach for your meter before you reach for your soldering iron.

19th May 2014, 10:37 am	#6
mole42uk Nonode Join Date: Aug 2010 Location: Resolven, Wales; and Bristol, England Posts: 2,613	Re: Heathkit Engine Analyser annoying fault! Hi Graham, The 250V is probably okay - I can move the spot fully left to right using the Horiz. Position control, and the vertical amp (also driven by the 250V line) is working just fine. There is no sawtooth driving the transistors. That's what I'm finding a real problem because it seems to be derived from the AC sine wave by Q610 and fed through SW1 to Q304 when SW1 is in the 'Calibrate' position. I can see a square wave at the base of Q601, but it has no signal on the collector. Q601 tests good and has also been substituted as a belt-n-braces approach. I am going to try and inject a suitable 50Hz signal into the base of Q702, the Horiz output transistor, make sure that moves the spot as I expect, then move back from there. I have to do some paid work for an hour or two first though :-( Richard

19th May 2014, 11:42 am	#7
dave cox Nonode Join Date: Jan 2009 Location: Bristol, UK. Posts: 2,062	Re: Heathkit Engine Analyser annoying fault! What's the voltage on Q601 collector? Do you see a signal on Q601 collector when its NOT in the CAL position? Working back the other way, Q701 is a level shifter. Does it show sensible voltages ? dc

19th May 2014, 12:19 pm	#8
cmjones01 Nonode Join Date: Oct 2008 Location: Warsaw, Poland and Cambridge, UK Posts: 2,679	Re: Heathkit Engine Ignition Analyser annoying fault! If there's no signal on Q601 collector, what about the resistor R604 from its collector to the positive supply? If that was open-circuit it could cause this problem. Chris __________________ What's going on in the workshop? http://martin-jones.com/

19th May 2014, 1:45 pm	#9
mole42uk Nonode Join Date: Aug 2010 Location: Resolven, Wales; and Bristol, England Posts: 2,613	Re: Heathkit Engine Ignition Analyser annoying fault! Q601 collector has about 34mV DC which is in accordance with the circuit. There is a signal on Q601 collector when SW1 is NOT in CAL position. The signal is a 40mV p-p pulse alternately pos and neg at about 50Hz. It disappears as soon as the switch is put into CAL, but when the switch is in anything other than CAL the collector isn't connected to anything except the 100k resistor (R604) Q701 was not showing anything sensible at all and testing the transistor out of circuit suggested it wasn't happy. I changed that but still no luck. Applying a 600mV 50Hz sine wave to the base of Q702 makes the trace move side-to side in the expected manner. Putting a similar signal to the base of Q701 does not make the trace move, yet I cannot find a fault with Q701, or the zener or the 4k7 resistor. Richard

19th May 2014, 3:25 pm	#10
dave cox Nonode Join Date: Jan 2009 Location: Bristol, UK. Posts: 2,062	Re: Heathkit Engine Ignition Analyser annoying fault! The zener (Q701 emitter) needs to be reverse biased into breakdown. You need to provide enough bias voltage to do this (Q701 base) with the sweep superimposed on top. If I'm reading it right, it will need LESS than14.4V less the zener voltage then less a bit more (your 600mV) to get Q701 into its operating region. Next back in the chain is the FET follower then the ramp integrator, around C401 (?) and current source Q402. dc Last edited by dave cox; 19th May 2014 at 3:26 pm. Reason: clarification

20th May 2014, 10:18 am	#11
mole42uk Nonode Join Date: Aug 2010 Location: Resolven, Wales; and Bristol, England Posts: 2,613	Re: Heathkit Engine Ignition Analyser annoying fault! Thanks to everyone who's helped so far. I still haven't made any improvement and after nearly two solid days I have to put the covers back on and take a break! I'll be into it again when my head has recovered! Richard