Zone VI VC Head, trouble

[dajaab]

Hi Everybody,

I own a Zone VI VC cold head but sadly one of the bulb, the green, doesn't work anymore.
Does anyone have an idea of where I can repair this head or at least have the schematic ?
The bulb is not broken, I think it's an electronic trouble but values on IC are erased ;-(

I can not resign myself to giving up this head, any help would be welcome

Thanks

[Eric Woodbury]

A schematic would be great. I've never seen one of these. I did own an Aristo VC head for a bit. It wasn't very complicated, but I don't know that Fred's is the same. You said no part numbers on the ICs, so you've looked under the hood. Perhaps post a few pix. One of the outside to see the controls and a few of the guts.

EW

[Luis-F-S]

PM Richard Ritter, hopefully, he can chime in. Also, the company that bought out Aristo has some replacement bulbs for some of their heads. Google is your friend. L

[dajaab]

I asked Richard Ritter, he said he wasn't at Zone VI/Calumet when this lamp was designed. He don't know.
LightSources sells remplacement bulbs but I'm pretty sure it's not the bulb, I think it's an electronic trouble. Maybe I'm wrong ?

Here some pictures

[Eric Woodbury]

Dajaab, Does one lamp work and not the other? I don't see any obviously burnt parts. Do you? Does it smell? Those are signs of major failure, but from what I see, it looks ok. People sand off part numbers to hide their design, but those 14p packages surrounded by resistors are probably quad opamps of the cheapest kind. I doubt they are damaged either, as once they are in a circuit, they are pretty tough.

Ask LightSources if they have a schematic.

Does this unit have photo diodes monitoring the lamp intensity? You would be able to see these mounted near the tubes in the lamp house. If so, that would account for some of the circuitry. It seems like a lot of parts for what it does.

Somebody here should have some insight. Obviously I'm worthless without a schematic or unit in front of me.

[Chuck Pere]

If each head is driven by similar circuitry maybe you can figure out some comparison checks between the working and non-working circuits. Start at the tubes and work back? You would need the proper test equipment plus be careful with high voltages.

[Eric Woodbury]

If you put a meter on the high voltage, make sure the meter can take it. Most meters are limited to 600V. It should be noted on the front of the meter. You can put a voltage divider at the front end with a couple (or more) of 10 Meg resistors. This will protect the meter. If you aren't familiar with any of this, then find ham radio neighbor or EE student.

Oh, you should check any wires from the pots (potentiometers) and switches Make sure none broken.

[Leigh]

Speaking as one with limited experience with Z VI heads, but LOTS of experience with vintage electronics...

The components with the highest probability of failure are the two blue electrolytic capacitors at bottom center of the first photo. These commonly fail at 10 to 20 years of age. Those in your head are much older.

They're relatively easy to replace, with two leads soldered to traces on the underside of the board. These caps are polarity sensitive. Normally the negative side is identified with dashes in that black line on the side. The lead closest to that line is the negative; the other is the positive.

Electrolytic caps have two values that the replacement must match, the capacitance and the voltage.
Capacitance is usually in microfarads, like 22uF (22mfd) or 47uF. Voltage is DC volts like 200DCV.

Your replacements must also match mechanically, specifically the diameter and lead spacing.
You may have some leeway in the height (length).

You can get replacements from Mouser Electronics:
https://www.mouser.com/Passive-Compo...z0yp7wZ1z0z7l5
They show capacitance units as uF, same as mfd.

Here some pictures

- Leigh

[Eric Woodbury]

Leigh, I agree, but I'll guess that those two caps are ok. If they failed it would take out the whole unit, not just the green tube, as they appear to be part of the plus/minus power than runs the entire board. Also, if they had failed, the tops would be puckered (typically). It is capacitor heating that kills caps, not time. It is the current in and out, heating the ESR of the cap. This unit doesn't seem to have a lot of hours on it, based on the fine condition of the chassis box.

Without more info and/or schematic, everything is speculation. I sure hope a schematic is found.

[dajaab]

Thanks to all for your interest

Some news:

I checked the two photo diodes, they go from 300K to 500Kohms when they are facing the lights
Same behavior for both, I think they are ok

I reversed the wiring of the lamps, the wires that went on the blue now go on the green.
And now, he green bulb works instead of the blue bulb.
So this first high voltage transformer works, and when I increase or reduce with the Hard control potentiometer on the control box, the intensity changes.

I checked the input voltages, both of these two transformers are well fed in 110V,
They each have a red and black cable, of small section, the control circuit I guess ?

I reversed these two control circuits, I still have the green lamp which works. But this time I can reduce or increase its intensity with the Soft control button on the control box.

I conclude that:
the two high voltages are supplied with 110v in primary section, (I can't check output)
the two control circuits red and black work,
the two bulb work if I reverse the wiring of the lamps,

it can only be the high voltage that is absent on the second transformer ? Transformer HS ?

What do you think ?
An idea where can I find this part?