Heathkit SO-4552 oscilloscope help needed

[Caleb]

Re: Heathkit SO-4552 oscilloscope help needed

The ring tester schematic is online as well, I built one for about 3$ mostly from junk box parts just had to order the 2 ic and the transistor (mouser has all the parts) I have found it very helpful in diagnosing inverter transformers.

I think popeye was saying you can connect the collector pin to the emitter pin with a light bulb in series to supply a current limited source for your hv transformer.

[wayne55]

Re: Heathkit SO-4552 oscilloscope help needed

I'm sorry I'm so slow, but do you mean to take a regular filament bulb and connect leads from the bulb to the emitter and collector holes where the transistor was mounted? Then turn the power on and if the bulb lights, does that mean the transformer is good?

[budm]

Re: Heathkit SO-4552 oscilloscope help needed

"I think popeye was saying you can connect the collector pin to the emitter pin with a light bulb in series to supply a current limited source for your hv transformer"
The DC resistance of the transformer will be very low, so the lamp will light up, it does not mean the transformer is bad, that is not real valid test due to low DC resistance of the transformer winding.
You can take the DC resistance of the transformer and see what you get.
When you feed the transformer with AC, the impedance of the winding will be the one that determine how much AC current will flow throug the winding.

[tom66]

Re: Heathkit SO-4552 oscilloscope help needed

A shorted turn would give the transformer very low effective resistance at AC frequencies, as well as at DC. I think the idea is that when the flyback is delivering power (and operating normally) it's got an effective AC voltage drop due to its inductance and the operating frequency, which draws considerably less than a shorted turn would.

[budm]

Re: Heathkit SO-4552 oscilloscope help needed

One or two shorted turn may not lower the DC resistance much if it has a couple 100 turns on it, putting lamp in place of the transistor will let the dc current flow through, the transfomer windig will act just like resistor, it has to be fed with AC. That's is why I ask for clarification of the lamp connection, may be the lamp in series with the transformer and with working transistor in place, not the lamp in place of the transistor.

[wayne55]

Re: Heathkit SO-4552 oscilloscope help needed

I got the parts quicker than I thought and after replacing the bad transistor, the filter capacitor, both HV diodes and the 237 8 pin chip, I'm now getting all the correct voltages in the power section. I get the +12, -12, +5 and +145 just as it calls for. This is with all components in place. I also get the AC voltages of 6.3 and 31 that feed from the main transformer to the CRT.

The bad news is that I still get nothing on the CRT display. The CRT rear end glows but no trace appears. At least now nothing seems to be getting too hot inside, but I did not think there would be more than 1 problem to deal with.

[budm]

Re: Heathkit SO-4552 oscilloscope help needed

You are going to need High voltage probe to find out if you do get 2KV or not from that high voltage section.

[wayne55]

Re: Heathkit SO-4552 oscilloscope help needed

I don't have a real high voltage probe, but I have a volt-pen that lights when it is near high voltage. I use it to check an electric fence. I do not think I'm getting high voltage, because it does not light up when I place it near the -2Kv checkpoint. Maybe the high voltage transformer is the problem afterall.

[wayne55]

Re: Heathkit SO-4552 oscilloscope help needed

One more thing to add, I do get the +12 volts at L162 and the -12 volts at L161 as shown on the schematic.

[Caleb]

Re: Heathkit SO-4552 oscilloscope help needed

Have you re-calibrated your vertical section? I had trouble getting my trace to appear on the crt (the position knobs weren't able to move it enough) until I re-calibrated the verticals, you also probably want to check the horizontal for correct voltages. I was able to measure mine with my dmm but my scope is only about 1100v (even though it says 1600v on the board) the manual says to expect about 1100v. Still hurts like a sob when you get too close.

[wayne55]

Re: Heathkit SO-4552 oscilloscope help needed

I contacted Pintek, the Taiwan maker of the scope. They said when the transformer went out, it normally took the transistor with it. Since the transistor was definitley bad, I assume that's what happened. There is a replacement transformer, but the cost of having it shipped and some kind of bank fee they charge make it cost prohibitive.