Manson hcs 3202

[semerchet]

Re: Manson hcs 3202

Hello Longbow, What do you know; I got it up and running!!!!!
Replaced C38 and Q3,4,5, and 6. While replacing the transistors I -just to be sure- looked for a datasheet and it turned out that instead of the original types of transistors there were something like a 2sb805 of 8055 something like that (not readable). The transistors I replaced also have a different pin configuration. Well anyway I no have a working power supply. I real, really appreciated your afford and help. Have a nice weekend.

[Longbow]

Re: Manson hcs 3202

Good show. I wonder if you found anything wrong with C38? Any leakage or faults in the transistors? Also, I am glad to know that we were focused on the proper section of the supply.

I had a feeling that the PNP part of the switches was not the best design. Now others will have a good place to check when fixing Manson supplies.

I have this circuit with TL494, etc built up on my bench and will send some results when it is complete.

[semerchet]

Re: Manson hcs 3202

Hi, I don'y know if it was C38 or the transistors. However I did know that the fault had to be there somewhere, so I thought I am gonna replace the 4 transistors and C38 and see where that gets me. Btw in the beginning I already replaced the Tl494, but with no effect.
I did measured C38 but it looked ok, and now whenever I find smd parts I am just gonna replace them. They cost nothing.
Greetings from a snowy Amsterdam.

[Longbow]

Re: Manson hcs 3202

OK, for those who might be interested...a few facts I have gathered together on this particular driver design using the TL494 along with 2 sets of current driver transistors. Please refer to the main supply schematics given on the first page.

First observation is that the TL494 is a soft start device and has no reason not to be. Thus, the drive waveforms on pins 8 and 11 do not produce an initial rapid output rise time. This chip needs careful attention to pc board layout since it does many things that tend to interact without bypass capacitors right on the pins - those include Vcc, Vref, 1/2Vref dividers, error amp inputs, etc.

According to the data sheets, output pins 8 and 11 will pull low to about 2 volts active low. That's not the greatest, since many transistors will easily drop below 1 volt if given enough base drive. Here is what I found questionable about the design from the first. The output pins on the IC produce (as wired up on this supply) an active low, followed by an open collector for their output. The NPN transistor in the current amplifier pairs is pulled up via a base resistor to the Vcc, but since the lower PNP base only goes to 2 volts active, it is not clear how it turns on to cause current in the primary of TR2.

As I suspected, connecting a 10Kohm load in place of the primary coil, a reasonable square wave is produced by upper and lower transistor pairs. The waveform "low" is about 3 volts, and the waveform high is 10 volts. Since the common emitters of the 2 transistors never goes below 3 volts, the PNP part can turn on with a base voltage of 2 volts, created by the IC. Let's face it - this is a crummy design.

But in operation, the circuit does not drive a 10Kohm resistor. Proper operation involves a relatively high impedance situation that drives a transformer primary. My guess the primary is designed to be parallel resonant at the drive frequency which is about 55 KHz in this case. A parallel LC circuit has maximum impedance at resonance. Then there is reflected impedance from the TR2 secondaries that (most likely) adds to the total load on the transistor pairs. All of this operation absolutely depends upon normal circuit startup. In my opinion, startup operation in this supply is left to chance, which works most of the time. I don't care for that approach much.

If the supply tolerances are just right it won't start, at least right away. In that case the upper and lower transistor pairs on the primary of TR2 get to drive a resistive load of under 1 ohm. I tried a 100 ohm load, and the transistors smoked from high dissipation. Also, the drive waveforms at pins 8 and 11 become in phase (instead of anti-phase). Looking back in this post we can see a scope pattern showing this, and the reason is as above, no startup, and high current, low impedance load to the transistor pair - probably already smoked.

Conclusion, the proper operation of the drive circuit depends upon startup of the main switching section and proper tuning of the primary tank on TR2. Operation of the driver IC is left to chance and may destroy the transistors. The fastest way to troubleshoot a supply that won't start is to confirm that the drive to the primary coil is push-pull and not forced parallel operation. Compare that method to a recent post showing a Tek scope that pulses the main supply every 5 seconds until it does start. But, that's Tektronix. That's the way I see it, anyway.

[semerchet]

Re: Manson hcs 3202

Thanks for the explanation

[danielgadelha]

Re: Manson hcs 3202

Hi all,
I have the same power supply HSC-3202 but this is 18V and 22A.
It doesn't mater what is the Voltage that I set I will have only 4.5V in the output.
When I change the voltage in the rotary switche, I can see the number changin but as soon as I finish to change the voltage, the 4.5V comes back to the screen and I only hae 4.5V always.
Somebody had this problem before?
Thanks