Will advise on Bowens Monolite monoblocs

Discussion in 'Lighting Equipment' started by hans_p._strobl, Sep 19, 2004.

  1. If you need information, technical data or advice on the repair of
    Bowens Monolite 200, 400 and 800 series monoblocs, I will be glad to help.
  2. Do you know what the watt-seconds are on the Bo-Lite units? These appear to be small units with simple half-full control.
  3. Sorry, Steve, I never bothered to collect data on the amateur grade flash unit Bowens Bo-Lite. These appeared about 1980 and were really simple in design. I assume they had about 125 watt/seconds (Joule). The electrical circuitry must have been close to the Monolite 200 E since it also sported the " low 35 VDC sync voltage". The full/half power setting in the Bowens design at that time was obtained by switching in resistors in series with the flash tube and the modeling light. When set to half power the modeling light resistor produces a lot of heat. This creates a problem, when the unit is mostly used on the reduced setting. Have a look at the image following which show the problem on the Monolite 200 E, and I bet it's the same on the Bolite. Greetings from Wuerzburg, Germany. Hans
  4. Thanks for offering to give advice! There is also another guy who has posted a partial schematic of a Bowens monolite 400 on the web: http://eddy.uni-duisburg.de/akurz/foto/flash.html

    I do not have Bowens units myself, but I'm very curious about different flash circuits. Hans, you posted photos of the inside of a Bowens 800E under another topic in this forum. From these images, I see two 50W resistors mounted on one side. Are these the flash adjustment resistors you mentioned above, or are they used to limit charge current when recycling?

    Also, would you happen to have a schematic or service manual to any more modern flash unit (in digital format)? The brand is not important, as long as it is one with fast recycle to full power (<2s).
    I would be very interested in seeing how things are done in current
    designs. Best wishes from Paris, France
  5. Hello Markus, here is the resistor panel of the Monolite 800E from a head-on view. There are 3 resistors 68 ohm each in parallel to each other. These are for current limiting in the charging circuit. The other one is a 2.2 ohm resistor thru which the last bank of capacitors will discharge to arrive at 1/8 power.
  6. Sorry Marcus, this time I got your name right.
    The Monolite 400 circuit diagram which Eddy shows on his web site is of a flash unit built somewhere around the year 1975. These units have wire wound coils in series with the flash tube instead of resistors for power control and are still in use worldwide. But once they break down, it's not worth to repair them.
    The Monolite 400 Series E and D are totally different in design and they are worth every cent spent for replacement of parts and repairs.
    The reason I chose this topic about the older Bowens equipment is because I feel there is a need to provide information for those who own such oldies which are not supported thru Bowens anymore.
    Having worked for both Hensel and Bowens I feel competent enough to tackle any task in this field, however I may not pass on specific information on newer type equipment which is still supported by manufacturers and their service organisations.

  7. Hans, thanks for the info and the extra image!
  8. Hi, Hans. Greetings from Singapore. Badly need help on 2 Monolite 750 Specials bought off e-bay. One was working, one wasn't because of a dead flashtube. Replaced but now both are dead!

    The previously good flash fired up fine initially - even popped it about 5 times at full power (switch at lo) - not sure if I got it right. Then I tried the newly replaced flash - it started smoking!!! although the modeling light was working. Then the overheat indicator came on.

    Tried the previously good unit and now it smokes as well!!! Modeling light was working fine but then there was a 'pop' and a while later, the overheat indicator also came on.

    Do you know what happened? I mean, it was working fine for at least one unit. I'll be most appreciative of an answer. No one here wants to repair and I hope to make it work with your kind assistance.

    Thank you,
    TW Mok
  9. Hello TW Mok,
    I am sorry to say that the repair of your Monolites will be costly and therefore not economical to do so.
    Evidently, your at least 26 years old Monolites 750 S's (produced until 1978) had not been in use for quite some time, and the capacitors had become unformatted. That would have been no problem, if you would have been aware of this and taken appropriate steps to format the capacitors of the unit. Now you have to replace all power capacitors. It's to late now, but for the future you do best to heed the advice below.

    Electrolytic power/storage capacitors begin to change their characteristic values after a certain period of time of non-use. This process, called "unformatting", begins to be measurable after about 2 weeks. Practically, this means that the capacity and, more troublesome, the maximum voltage it can operate on is greatly reduced. So, after long periods of non-use, and whenever you are not certain how long the unit has been idle, you have to take specific steps to avoid the unit going up in smoke.

    The following procedure applies to Bowens Monolites only, because the power capacitors of these units are always, regardless of power setting, charged to maximum voltage.

    Determine the exact type first, and select the correct procedure, A or B:

    A. Formatting of power capacitors for Bowens Monolite 200, X 200, 400, X400 and 750 S only (the ones with the silver grey housing and the slow charge feature).

    1. Do not connect the unit to the mains as yet.
    2. Make sure that the power switch is in the off position (so it's NOT pointing towards the flash tube symbol)
    3. Connect the unit to the mains. Do not turn it on as yet.
    4. Now, the next exercise is to turn the unit on for the duration for TWO SECONDS only.
    So take a deep breath, throw that switch ON and turn it OFF after 2 seconds, and leave it OFF !
    5. Wait for approx. 5 minutes.
    6. Now repeat step 4. But this time, leave the unit on for FOUR SECONDS. Then turn it off.
    7. After 5 minutes, turn the unit ON. It should start out in SLOW CHARGE and change to READY after 8 seconds. Leave it on for at least ? hour before you trigger the flash.
    There is no need to trigger the flash needlessly! The discharge of the capacitors always puts a strain on them, especially right after the formatting procedure. So, avoid popping off needless flashes----the gas in the tube doesn't need formatting--- it just makes dealers peddling replacement tubes happy.

    B. Formatting of power capacitors for Bowens Monolite 200 B+E+D, 400 B+E+D, 800 B+E, (the ones with the black housing and without the slow charging feature):

    1. Do not connect the unit to the mains as yet.
    2. Make sure that the power switch is in the off position (so it's NOT pointing towards the flash tube symbol)
    3. Connect the unit to the mains. Do not turn it on as yet.
    4. Now, the next exercise is to turn the unit on for the duration for ? second -ONE HALF SECOND- only. This means "on" and "off" real quick!!!
    So take a deep breath, throw that switch ON and OFF, and leave it OFF!
    5. Wait for approx. 5 minutes.
    6. Now repeat step 4. But this time, leave the unit on for ONE SECOND. Turn off.
    7. After 5 minutes, turn the unit ON. The READY light should come on after 2 seconds. Leave the unit on. Do not trigger the flash before at least half an hour has gone by. Like I wrote before, there is no need to trigger the flash needlessly!

    Different flash units call for a modification of procedure.

    Hans P. Strobl
  10. The 1/2 showed up as ? in the text. Under section A it should read: 1/2 hour; under B it should be: 1/2 second.
    Sorry, I wrote the text in MS Word and missed it.
  11. Dear Hans,

    Thank you very much for taking the time and trouble to answer with such detailed advise. Bless your heart.

    What a shame though, that my 2 Monolites should literally go up in smoke in my ignorance. I thought I had a good deal and was looking to save up for better lights. To think that I've also bought 2 new spare flashtubes as well.

    I'll certainly keep those instructions of yours handy. You've been more than helpful. That was a lesson in itself.

    Thank you again & have a great day ahead,
    TW Mok
  12. Hello TW Mok, save the flash tubes. They can be used on all other Monolites up to 800 E. The rest is good for spare parts, especially the power setting switches. Next time you buy a used flash, drop me a note first.
    What I would like to know is, how much did you pay for the flash units and the replacement tubes, and where did you buy them?


    Hans P. Strobl
  13. Hi, Hans. Thank you for your advise. Will follow your good advice. The pair of Monolite 750 Specials cost me around US$250 including sea shipment. The spare flashtubes (both new) cost me around US$50 each. Bought them from 2 separate sources off e-bay (one from US, the other in Canada).

    I was able to find some photoflash suppliers in Taiwan and China. Wonder if they are any good. Will remove the covers to one of my 750s, discharge the capacitors anyway (just to be safe) using my 10W 24 Ohm resistor and see if I can manage to find any Chinese equivalents. The only thing is that they only sell in quantity.

    It was also interesting to find out as well that there are shops in Shanghai selling new flashes of the Bowen design. Most of them use the new 'S' reflector mounting, though but might be worth a try just to allow me to use the same flashtubes.

    Of course, the other way is to look out for some 400s or 800s like you recommended elsewhere. Only difficulty seems to be to find those running at 240Vac.

    Have a great day,
    TW Mok
  14. Hi, Hans,

    Need your expert advise again. Took apart my Monolite 750 and found the capacitors to be Daly PF K4 63/10/6 BTD. They are 38mm diameter & 78 mm tall. There are 7 of them just taped together and soldered in multiple series. Would you happen to know the values, pls? I've tried to find Daly capacitors or their equivalents to no avail. I've got photos of them if that should be helpful to you.

    Anyway, I've managed to locate generic 850uF 370Vdc photoflash capacitors 35mm diameter & 90mm tall. I can figure out how to pack them in but can you advice if these are usable replacements, pls?

    I don't mind not getting the full 750 watt seconds of output but just desparate to get the flash working to at least earn some money for newer lights. Or perhaps to even just pay for them first & break even for the price of the spares as well.

    Thank you very much for your trouble,
    TW Mok
  15. Hello TW Mok, are you sure you counted just 7 capacitors in the Monolite 750SP?. There must always be even numbers like 2, 4, 6 or 8 for the different power values. This is because 2 capacitors are connected in series be able to operate at 640 VDC. The balance between the the top and the lower bank of capacitors is very important. Even with the right number of capacitors is hard enough to achieve electrical balance due to varying capacitances of each one . With uneven number you are bound to have trouble. The capacitors are originally Daly's with 1000 mF and 350 VDC rating. The 850 mF/370 VDC should be ok if they are specified for photoflash use. The 35 mm diameter is perfect. The image shows a pack of 8 capacitors also with 35 mm diameter for replacement in the 750 SP. I marked the plus (+) pole with red paint. In the second row you will find the minus(-) pole of the left capacitor connected to the plus (+) pole of the capacitor on the right. This is ok . Remember that bank 1 is in series with bank 2 ! To form the pack you have to arrange the capacitors on a flat surface and wrap them with tape so they can not move anymore. Following this you cut and bend pieces of thick insulated solid wire from which you remove the insulation in the appropriate places (where the solder lugs are). Don't solder as yet, make sure everything fits before you start to take the iron to it. It should be at least an 80 Watt type for hot and quick work. It's best to tack the wire lightly to the lugs first, allowing small adjustments in position if need be, then solder properly with more solder material applied. Don't bend the lugs up too much, just raise them about 1 mm above the lid. Use a strip of thin cardboard underneath the lugs when you solder. There is no need to route the wire thru the eyes of the lugs, it's more important that the insulation between the connections is not impaired. When the pack is finished, put double-sided tape on the bottom of it and put it into position between the 4 aluminium rods, applying pressure so it will stick on the plastic support. Stabilize the pack so it can not move mechanically. Now you can connect the stranded wire according to the image.
  16. As to your flash tubes, they can be used with Monolites 200 to 800 series only. Next time you invest in used Monolites, stay away from old 200, 400, 750's. They were produced as early as 1968. They have reached the end of their useful life. I wonder about the price people are still willing to pay for these. I think that they are worthless in trade. They have a 200 VDC sync voltage and will fry the sync circuitry of modern digital cameras unless used in combination with a Wein Safe Sync. Younger Monolites 200E, 200D, 400E, 400D, 800E, 800D are of different electrical design and are ok to buy. They have sync voltages of 35 VDC. The Bowens Monolite 200 B, 400 B and 800 B were made for Bogen, USA and run on 110-120VAC only. Sync V is 200VDC ! By the way, you can't discharge a flash unit with a 24 Ohm 10 Watt resistor! This will draw a powerful arc and will destroy the tip of your test lead, not talking about the possibility that you may be jumping out of your pants when you hear that cacophonious sound that the arc will produce. You need at least a 4.7 KILOOHM resistor, wirewound and with a rating of 10 Watt minimum. Enclosed is an image of a device that I made for discharging capacitors.
  17. Take a photo of the defective pack and post it or send it to me. Perhaps there is an alternative to new capacitors by removing bad ones out of the pack.

  18. Hi! I've been reading your excellent advice about Bowens Monoblocs and thought that you might be able to help me with my issue.

    I've come into possession of 2 Bowens Monolites, one 400CX and one 400B. I have absolutely no idea what the difference between the two is - they look identical from the outside besides the model number markings.

    Anyways, the 400CX seems to work fine, but the the 400B seems to fire only at 1/4 power no matter which setting the power-slector knob is turned to. I saw your responses about the failure of the knob and thought that might be my problem.

    I had taken it in to be fixed, but I got an exorbitant quote of like $400 Canadian...

    I would really appreciate hearing any thoughts you might have. Thank you!
  19. Hi Ben,
    the main difference between Bowens 400CX and 400B is in the model suffix, the "CX" stands for the Canadian version, and the "B" for the US version imported by Bogen Photo of New Jersey. Both have the same control PCB (printed circuit board). The charging circuitry is based on a voltage quadrupling circuit, raising the 120 VAC mains to 620 VDC for charging the power capacitors. Both units have a voltage of approx. 200 VDC at the sync jacks, therefore I recommend the use of a Wein Safe Sync on the camera when using a sync cable, or one on the master flash unit to be triggered when using a remote triggering device (to protect the receiver part).
    When the power selector switch goes bad on the Monolite 400 you will have no output at all or 1/4 power, depending on where arcing and burn-off occurred. Because you say the unit fires at low power in all positions of the rotary switch, I assume that the damage to the switch is such as to make the energy of the power capacitors go thru the complete chain of tapped power setting resistors always. If I am correct in my assumption, installing a bridging wire in the correct place will get you FULL power. In order to regain control over partial power settings a new rotary switch would have to be installed. The problem is that the original switch is not made anymore and that there is no direct replacement unless you use one from a salvaged unit.
    Do you have any qualifications to work with electrical equipment? Or do you have someone who does?
  20. Thank you for the quick answer! It's nice to know the meaning of the model number suffixes, and very good to have the tip on using a sync safe. Full power will certainly be more useful than 1/4 power, so I will go find an electrician to install the bridging wire (I'm not confident in working among big capacitors myself). It's too bad there aren't any replacement switches, though.

    Thanks again!
  21. Hi, I've just posted a question for you Hans under the title of Bowens monoblocs on the Lighting forum, Regards Phil.
  22. Hi All,
    after my tech has said that he can't find replacement caps for my 800e, i embarked on a bit of googleage to find some, and have come across, possibly, a supplier. www.epcos.de supply flash caps. however if both the 800e and the 750 special take 350vdc 1000mF caps, they supply item no. B43416A8108A000 rated at 330vdc and 1000mF, or the no. B43416A9118A000 which is 360vdc and 1100mF. which of these two options is more suited, and less likely to cause overheating? these are miniature compared to the originals, and made for photoflash applications. any tips would be appreciated.

  23. are you still around?
  24. I am, but no progress to report.

  25. Hi Hans.
    I am the happy owner of a Monolite 400, unfortunly it has some bad capacitors, the pre-charge stays on. But the ones in my unit, as you can see on the picture, are DALY PSFT X34 63/10/6CW, thise are 5 cm Ø and not 3,5cm. like the ones mentioned above.
    Is this an earlier model or?
    Can I still use the 330V 1000 µF from epcos.de ?
    Kind Regards. Lars Hansen
  26. Lars, the Bowens Monolite 400 you own is of the very first series of mono bloc flash units ever made by Bowens of London, matter of fact, they claim they are the very first ones to put a compact flash unit on the market in 1968. The Daly capacitors DALY PSFT X34 63/10/6CW you show are probably at least 31years old and the electrolyte may have dried up to an extent and the oxide film on the anode aluminium foil may have deteriorated very much, decreasing capacity and increasing the leakage current. However, you can not necessarily deduct from the fact that the pre-charge neon on the Monolite 400 stays on that the capacitors are bad. That symptom is also present in numerous other faults in the control circuitry; replacing the flash capacitors without knowing the true fault may be throwing money out of the window. Therefore, you should have a technician with experience in the repair of flash units take a look at the Monolite to find out what is really wrong. Perhaps it is just the transistor that is sitting next to relay 2 or3? That's a 25 Cent part!

    If there is the need to replace capacitors you may have a problem to accommodate them physically. The old ones are 50 mm in diameter and are mounted by a stud, and new ones in capacitances around 1000 µF will be 38 mm in diameter, and without stud. This calls for adapter plates and spacers to keep them in place securely.
    "Can I still use the 330V 1000 µF from epcos.de"
    I'm afraid not. You need the 350V types at least, or better yet, the 360 V ones. The working voltage of the old Monolite 400 is 640 VDC unregulated, therefore the flash capacitor pack is made up of 2 banks in series connection to be able to operate at that voltage. If capacitors connected in series change their electric properties, especially their capacitance, the imbalance in the set up may drive one or more capacitors into over voltage condition. Using 330 V capacitors in a 640 V series connection set up in an unregulated charging circuit as found in the old Monolites is literally asking for trouble. When the voltage applied exceeds the insulation capability of the anode foil, liquid electrolyte and the separating paper layer the capacitor will react violently and may explode with a loud bang.
    Hope this helps
    One last note:
    How about closing this thread and opening new ones with more specific titles. Would make manoeuvring easier. Thanks
  27. Hi Hans,
    I have just bought a Monolite 800E (130$ with a strong Manfrotto stand) without user manual. It strobes at all powers and seem to have not any troubles, but I've some doubts:
    1. the READY 'red lamp' always is blinking (initially slow and then gradually stronger, but it never becomes 'fixed red').
    2. The botton with 'flash icon' (on the right of control panel) seems to have not an effective ON / OFF role.
    Is this normal or signs of looming troublesomes ?
    For its maintenance, is it a good idea to sometime repeat your 'capacitors formatting procedure' ?
    Its sync connection is by a 'peanut'; can I use instead an inexpensive Wireless STUDIO Flash RT-16 TRIGGER
    IMPORTANT INFO: If somebody is still looking for a spare flashtube, he can find it here (£ 66 + VAT):
    All further suggestions or advice would be appreciated.
    Thanks for any answer.
  28. Hallo Hans,
    i have a question?
    On my Hensel(same as Bowens Mono) the ac powerjack is broken![​IMG]
    And i want to change it. The question is how do i get there?
    Do i need to discharge the flash? Someone told me that I can discharge the Flash by pushing the test flash button immediately after turning the flash down (does it works?)
    i saw your photo with open Monolite:
    as i understand to get to the power jack i need to take off , all the back wit all the dials?
    i will be deeply grateful!
    ich werde Sehr dankbar sein!!!
    rgds Toms
  29. Hi Toms,
    it is not a safe place to go. getting at the back of the chassis involves removing the whole case, annoyingly. you can't just remove the back. Discharging the unit is best done with a large resistor on aligator clips attached to the tube contacts (once removed). but as I said and Hans has pointed out, these are dangerous high-voltage units. I have a habit of leaving the resistor in place across the caps whilst working on a unit.
  30. Hi T Feltus,
    thanks for your response! I just bought 4700 Ohm resistor, 11 w, and alligator clips! Is it save for a flash tube, to attach a resistor on tube contacts? When I will connect the resistor would I fell or see in some way that the flash is discharging? I have the volt meter but its cat 3 till 250v, can I use this one or the flash is at higher voltage?
    brgds, Toms
  31. Hi Toms,
    no no, take off the tube. there are two small screws near the modeling light, the reflector and tube assembly comes off, exposing three contacts labelled as "high voltage", so clip the resistor on there (and put the resistor inside a box so you don't touch its wires).
    the operating voltage, according to Hans, above, is 640vdc, so i would leave the resistor on for a couple of minutes before checking. The 400 should have a good dump circuit, but it is never worth risking even with a disposable flash.
  32. Hi T Feltus , I wonder if I may ask for some help ,During the recent cold spell in the Uk two of my Bowens Monolight 400's became unusable as tempratures fell well into minus .
    the units were not used for a month , on use units were swiched on and left to warm with Modelling lamp on ,on switching to flash charge and ready lamp worked fine but unit will not flash by either test button or wireless trigger ,there was no smoke no bang no nothing ,any pointers would be very greatly appreciated ,unit is now totally stripped and nothing found ,are the circuit diagrams available anywhere .
    Thanking you Paul.
  33. I might have them for the 800E which is a little different. I have no idea how the cold could have affected the unit however. if the charge light is coming on, then i expect that the caps are charging ok. did you (carefully) measure the voltage at the tube contacts? The first thing to try, I think, is to check tube voltage, then also check the sync voltage to make sure that it is not the trigger circuit that is gone. the sync voltage should be 35VDC.
  34. thanks for the response ,two units gave up ,I assume during this spell as the room they were in became very damp as well ,just decided not to flash ,will try as you say tube voltage etc .one component I assume is suspect is marked RCA 7647 :D3202U and I think feeds a power reg transistor , ah ! it's all coming back to me ,slowly I hope .
  35. Hi,
    A friend of mine tried to use his studio lights on a diesel generator. Both burned out instantly.
    One is a Bowens Mono Gold and the other one is a Hensel Compact-B 1000. Both of them have the capacitors from the voltage doubler swollen and leaking.
    The Bowens capacitor is marked with:
    24uF RED HT
    NP 224 350
    H00 BSS
    and the Hensel capacitor is marked only with an internal cod: HENSEL SK 3
    My problem is that I don't know the values for the Hensel capacitor, but also for the Bowens, everything I found on the market are really small capacitors (meaning dimensions) and I don't think that they are good replacement.
    Does anybody knows what value the Hensel capacitor is and can you please direct me to a store where I can find these kind of flash capacitors. I've searched the net and I found some stores, but they have only the big (value) capacitors for the main bank.
    Thank you
  36. Hello Hans!
    This initiative of yours is very kind.
    I have occasional problems with my Monolite 800E monoblocks. Sometimes one of them just refuses to fire. Manually or with synchro cell or cable, it is the same. It charges, the "ready" light is blinking normally, but it just doesn't fire.
    I have this guy that took a look at them and he doesn't know what is wrong. He just resolders some points that seem suspicious to him and the flash works well again ... for some time.
    He asked me if I could find a circuit scheme. Can anibody help me finding it somewhere?
    Thank you in advance.
    Regards from Croatia.
  37. Hi there,
    I have a couple of old Bowens 750w Silver monos that I think haven't been used in a while.
    What would the formatting process for the capacitors in these be?
    I'm thinking the "B" one as the housing is black but am aware this model wasn't specifically mentioned. Could anyone put my mind at rest please...
    Thank you
  38. Hi Guys,
    Hans seems to have vanished, sadly. And also I have not really got very far with my Bowens units, in fact, I have 4 in a box dismantled.
    Aaron, I am not aware of a black 750 existing: the 750 I knew of was one of the older designs, with pressed aluminium caps on the casing... If your black one is like these, I think the design is a lot simpler than the later black ones. Said this, I have two silver 200s that I have not got working, as some of the peculiar proprietary components baffle me.
    Dag, I do have a partial schematic, but it is of the 400e, and obviously of the pre-charge component that the 800e does not have, so it is of little use. I never found a full schematic of any of these units.
  39. Thank you T Feltus, I have only 800 Ws units.
  40. Hans - thank you for info posted long ago on old Bowens heads. I was about to dump my old bo-lite but thought to look for spare parts and/or info before burial. Nothing to lose I went through a version of the 1/2 second - 1 second - 5 second power up routine and amazingly after 15 mins charge I got a pop on test button. It's not very powerful but the barn doors and grid have made it very useful to me - it has been a key light in many a set-up so deep gratitude to yourself - made my day. Derek Simpson

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