Mastech HY3010E-3: "slave" side not working

[BradysDad]

Hello, all!

I just got a used Mastech HY3010E-3 and it appears to work fine in PARALLEL and SERIES modes but in INDEPENDENT mode, slave side does not function at all.

I do have the two pushbuttons popped all the way up to activate INDEPENDENT mode to no avail.

The free-standing 5V section works fine (4.89v on the meter).

Also, FWIW, I can't adjust the AMPS at all on either side, regardless of the mode.

I repair arcade games and pinballs as a hobby, so I'm hoping with some guidance or a schematic, I may be able to repair this.

UNLESS - it's not broken and I'm missing something. I have RTFM and there doesn't seem to be any mention of an overload reset procedure for this model and I have tried all the suggested settings (dials fully clock-wise, etc.). Does the slave side need a load to operate properly perhaps - no mention in manual either way.  I did try it under load to no change.

TIA!

[jchw4]

I have never seen HY3010E-3 inside (it is supposed to be switch-mode), but I repaired HY3005D-3 (a linear one).

There are stilll some similarities:

• Both are sold under many brands. You may be lucky searching for schematics under another brand.
• Both have single-channel versions. Googling suggests that people are using single-channel version HY3020E schematics as a base for debugging.
• Face photos suggest similar build quality.

Based on my tiny experience with these I think it's nearly impossible to find the exact schematics. But searching for sister models will give you enough data.

You will probably need to do some tracing. Just take PCB photos and do tracing either on printed photos or use your PC.

Build quality is not the best. In my case the worst part were several wires that got broken inside the insulation. I think one was broken at 2 spots. Device had about 10 years in service.

Your description suggests an issue around the modes switch. Could be a broken wire.

Can you share some photos inside the unit?

[Swake]

About the amps setting. The meter is showing what current the power supply is delivering. The knob to set the current is a 'maximum' knob. To set the current to a certain maximum value you short the output and turn the knob to the desired value. Obviously you remove the short after that and keep this procedure as quick as possible.

[BradysDad]

Good idea on the other brand's schematics.  Will try that avenue.

Also, while I'm sure the base is similar, the 3010E-3 has four daughter boards in it as well that the base model doesn't have - presumably two for the master and two for the slave. Without those schems/layouts, still kind of shooting in the dark.

Will check the wiring next time, too.  Good to know it's a problem point with these.

[BradysDad]

FWIW. . .

R204 and R203 were fried and Q202 and Q203 popped.

Replaced all and Q202 immediately popped again.  Q 203 tested and also bad again but not visibly damaged.

I assume the "2" series is the circuit for the SLAVE and the "1" series for the MASTER as they seem to be identical circuits. 

So, something in the SLAVE circuit is popping the lid off Q202.

Traces show that connects to Q203 and to a couple of transformers on the main board as well.  May try swapping out the identical circuit transformers to try and troubleshoot which one is bad.

Other suggestions welcome.

[Swake]

Share schematics please, and if you didn't find them you can retrace it partly yourself or at least share clear pics from all sides. We can't help without information.

From what I understand this is a SMPS not a linear version. If the output stage of such a thing goes bad it is not uncommon to have a whole series of semiconductors to die, not just one or two and maybe also some caps might have suffered. You'll really have to check everything.  Damage is seldom visible.

What are those transistors you mention? How do you know the parts you replaced them with where ok? If you sourced them from Ali-something expect these to be fake and potentially having very different characteristics from what it should be.

Why do you suspect the transformers? Not saying these are not damaged somehow but these things rarely go.

[BradysDad]

Closest schems I can find on it attached.  Q202 and 203 are the part number shown on the schems.

Parts ordered from a U.S distributor so presuming they are legit.

Suspecting transformers as they are next in circuit.

[Swake]

If that is a reputable source like Mouser or Digikey you're probably good. If it was a secondary distributor you'll have to check what you have at hand.

Check all components directly to the left of those 2 transistors. The 4 diodes but also the caps. Verify that traces are still working as traces.

Careful! some pretty high voltages in that area, make sure the caps ( especially C6/C7) are discharged. Eventually use a 100kOhm resistor to ground, do NOT short them. Else you're going to remember that zap for a very long time. Also UNPLUG the PS before checking, never trust the switch without double checking it effectively switched off.

[BradysDad]

Not the transformers.

All the 200 series diodes checked out of circuit, as well as the 6A10 diodes (there are 8 on this rig) to no avail. 

I do not have the proper caps to replace any of the larger 200 series ones but none test as "open" which I've found to be a pretty good indicator that a cap's bad.

So, right now I have the dedicated 5V port and one of the adjustable ports working, just not the final one (slave). 

[Swake]

Let's see if the TL494 and surroundings are alive. First check that Vcc is present (see H1 feeding D105 and C103/107 on the bottom of the schematic that is in fact coming from the transformer T101 on the top of the schematic).
Then verify there is a saw-tooth signal on pin 5 of the TL494.

If Vcc and signal on pin 5 are ok then check the output signals from C1 and C2 on pins 8 and 11 of the TL494. Follow this PWM signal over the inverters in the 4069, then over the transistor pairs Q301/303 and Q302/304 up till between pins 6 and 10 of the transformer T201.

Compare the measurements with the working channel. Preferably use a scope with floating inputs or a differential probe. If you do not have a differential probe then only connect your scope on the secondary side of T201; T201 and T202 else you'll have fireworks and blow up the scope.

The datasheet for the TL494 from Texas Instruments shows what kind of waveform to expect.