Hickok 440 Curve Tracer Repair Help

Have you replaced any and all electrolytic capacitors and verified that the resistors are on spec?

Capacitors are bigger suspects than the semiconductors...

John :-#)#

ing, even though it is a relatively simple circuit.

ion. It looks like noise comes and goes and distorts it. I have replaced mo st of the semiconductors. The 15v power supply is a bit low at about 13.9v, though the regulator transistor and zeners have been replaced.

I changed the two electrolytics in the 15v supply, and one polyester that i s used in the base generator section (though it tested OK out of circuit). I did a quick run through on the resistors while in circuit, and they test within spec with nothing unusual.

In older equipment it is always to suspect the electrolytic capacitors first. For older tube equipment the 1/2 and 1 watt carbon resistors often seem to go up in value and are the next thing after the capacitors I check for equipment that is sort of working,but not up to specifications.

ing, even though it is a relatively simple circuit.

ion. It looks like noise comes and goes and distorts it. I have replaced mo st of the semiconductors. The 15v power supply is a bit low at about 13.9v, though the regulator transistor and zeners have been replaced.

So the short answer is Yes.

OK, caps and resistors all good.

Then I'd scope the existing power supply to make sure it is clean & stable.

If you have a good bench power supply see if using a different +15VDC source clears up the issue.

John :-#)#

ooting, even though it is a relatively simple circuit.

ration. It looks like noise comes and goes and distorts it. I have replaced most of the semiconductors. The 15v power supply is a bit low at about 13.

e.

I can do both. I did not think of an external power supply, will report bac k and post results.

Thank you

Typically, there's a monostable making a current pulse into a capacitor for each step. If the capacitor is an electrolytic, it may be leaky now (but run the staircase overnight before you replace parts, it may be that some ON-time will reform the oxide layer). If the monostable has a capacitor, it is also a suspect (unstable times).

Resetting the staircase there's a charge-dump (transistor?) that could be leaky, or its drive might be picking up noise. Hanging an o-scope probe onto the step generator to show the rise/plateau qualities will tell where the problem lies.

oting, even though it is a relatively simple circuit.

or each step.

ircase

rm

ct (unstable times).

leaky, or its

generator

Yes, this is the way it works. I should attach the schematic and circuit de scription. It charges a ceramic non electrolytic capacitor, with a diode in line that keeps it from discharging each pulse. But since ceramics rarely fail I did not change it, but maybe I should. And from previous scope probi ng I saw various qualities of pulses but did not really understand what was normal and what was not.

Thank you.

You can't attach things here. Bama probably has it but I can't confirm it r ight now because of this wonky MODEM that is going back to SBC with stab wo unds, three bullet holes and half burned by a Bernzomatic torch. I am serio usly about to jump ship but the only other thing I can get here is Hughesne t and in this area since there is a temporary rain forest to the south ever y year it is going to drop when it rains south of here just like the Dish T V thing.

But you probably got it online, just throw up a link.

I suppose I don't have to tell you to scrutinize every small signal PNP in there right ?

Nice thing is they all work the same. You should be able to put a low value resistor on the base drive and derive current that way. the noise and what ever have to be there. You can leave that on one channel of the scope and j ust start going backwards with the other. Unless you already have, if you a re sure it is at the beginning of the "chain".

Nice to have it localised of course but when things get old they get weird failure modes. I have seen PC boards that worked for more than a decade and then came to me and looking for a bad connection on the board bending thin gs a huge piece of solder simply came off the copper. It wasn't clean enoug h when they wave soldered it but it took all that time to manifest itself.

I think on this unit you are probably down to the small caps. some of them like to be a piece of wire sometimes.

More later, I am going to go shoot the MODEM. Don't worry I got another one .

They don't.

I looked everywhere for it and ended up buying the hard copy. So I need to scan it and link it.

Here is a photo gallery that I created with the schematic and circuit description: