Replacement for an old BRY39 Programmable unijunction transistor - Page 1
Forum section: electronics / repair

author: gkmaia
author_rank: Frequent Contributor
timestamp: October 23, 2020, 04:55:01 am
content: Would anyone know a modern replacement for this little fella?https://datasheetspdf.com/pdf/123036/NXP/BRY39/1

author: Ian.M
author_rank: Super Contributor
timestamp: October 23, 2020, 07:22:21 am
content: I'd be delighted to be proven wrong, but I don't think there is any small signal PNPN four layer device with both anode and cathode gates brought out in current production.

author: gkmaia
author_rank: Frequent Contributor
timestamp: October 23, 2020, 09:03:27 am
content: I thought so... now I am gonna have to get a recycled from china and wait a month...But I am trying to figure out how this thing works so I can test it. Could you give me a hand understanding how this arrangement works.

author: srb1954
author_rank: Super Contributor
timestamp: October 23, 2020, 09:04:08 am
content: Quote from: gkmaia on October 23, 2020, 04:55:01 amI can let you have some BR101 Silicon Controlled Switches.These are a 4-layer device with similar construction to a PUT. Perhaps you could modify your circuit to use these instead.

author: gkmaia
author_rank: Frequent Contributor
timestamp: October 23, 2020, 09:14:49 am
content: thanks srb. I appreciate.I really don't want to modify the circuit as it is part of feedback circuit of a scope I am restoring. At the moment it is not switching and it is stuck.actually, there is a way I can test it.by connecting a, ag and kg as a PNP transistor on my tracerby connecting kg, ag and k as a NPN transistor on my tracer

author: aqibi2000
author_rank: Regular Contributor
timestamp: October 23, 2020, 09:20:43 am
content: Are you sure the grade of this component is critical to you? As long as it has high BW.By the way the thing is configured it’s almost like an inverter:

author: srb1954
author_rank: Super Contributor
timestamp: October 23, 2020, 09:25:11 am
content: Quote from: gkmaia on October 23, 2020, 09:14:49 amLooks like a Philips circuit.

author: Ian.M
author_rank: Super Contributor
timestamp: October 23, 2020, 09:29:24 am
content: The anode gate is effectively not used (although R6007 does reduce the sensitivity of the cathode gate a bit by killing the gain of the transistor action of the top three layers of the device (PNP) at low currents), which means you could probably substitute a sensitive gate TO-92 small signal SCR, however as this is part of the control circuit of a switched mode PSU, if the BRY39 is known to be faulty, exact replacement with one from a reputable specialist NOS supplier is strongly recommended.

author: gkmaia
author_rank: Frequent Contributor
timestamp: October 23, 2020, 09:43:58 am
content: It is a philips scope. Right on point.Also yes Ian, as you described it is either a NOS or an equivalent. But cannot find a equivalent.I am going to test it tomorrow and see if it is actually faulty.

author: akimpowerscr
author_rank: Regular Contributor
timestamp: October 23, 2020, 10:44:37 am
content: I believe you are looking in the wrong direction.It is a self-oscillating smps, so there may be a lot of reasons for it not to oscillate.You suspect the bry39 only because you don't understand how it works and it's probably a mistake.If it were faulty (other than anode-cathode dead short), the mosfet V6014 would burn immediately.Indeed, its function is to limit the peak current in the V6014 mosfet by blocking it as soon as the current has reached a certain value, which can be modified by the optocoupler current H6001

author: gkmaia
author_rank: Frequent Contributor
timestamp: October 23, 2020, 11:22:44 am
content: I've got quite a few faulty parts on this primary.V6004, V6002, V6018, C6011, v6112 were faulty. That is what I found so far.That is correct I do not understand how it works, but not really putting my bet on it. Hard to know if it is working with so many faulty components.So I lifted all secondary diodes and removed the voltage control opto to try to isolate the primary. But testing some of the key primary components before plugging the thing back.If I can get it to oscillate I will then bring back each of secondary rails at a time and the voltage control.Would it not be more likely that the V6018 would fry if V6014 were stuck on?

author: Chris56000
author_rank: Frequent Contributor
timestamp: October 23, 2020, 11:47:08 am
content: Hi!If you register on the UK Vintage Radio Restoration Forum, or have already done so, submit a post in the "Parts & Service Information Wanted" section, you can request a BRY39 on there, they were used by the thousands on early Solid State CTVs as the Field Oscillator, failing that:–https://www.ebay.co.uk/itm/272971024354Chris WilliamsPS!What Philips scope is it? If I know which model no it is I can help go through it for you with repair advice!

author: akimpowerscr
author_rank: Regular Contributor
timestamp: October 23, 2020, 12:43:06 pm
content: It seems to be a PM3055What about to open a new topic on Philips PM3055 SMPS repair ?

author: jdragoset
author_rank: Frequent Contributor
timestamp: October 23, 2020, 12:57:10 pm
content: https://www.ebay.com/itm/BRY39/142326559329?hash=item212352f261:g:ZxQAAOSwzgBY1Av-

author: Ian.M
author_rank: Super Contributor
timestamp: October 23, 2020, 01:34:41 pm
content: Why would you trust an EBAY seller who cant even get the product photo right?BRY39 should be a four lead metal can TO-72 package, not a three lead TO-50 RF 'pill' package!

author: jdragoset
author_rank: Frequent Contributor
timestamp: October 23, 2020, 06:30:08 pm
content: The seller corrected the pic (re-check the link) and is willing to accept offers.Seems they do ship to NZ.

author: akimpowerscr
author_rank: Regular Contributor
timestamp: October 23, 2020, 06:32:48 pm
content: Why look for a BRY39 when you probably don't need to replace it ?It is easy to briefly test the BRY39 since it is only the equivalent to a set of two PNP and NPN transistors.We have access to the base-emitter junctions of each of these two transistors.If these two junctions are good (test with a multimeter, diode function), there is a 90% probability that the BRY39 is not defective.

author: Chris56000
author_rank: Frequent Contributor
timestamp: October 23, 2020, 06:34:44 pm
content: Hi!I read your post about 4 posts back in which you thought of trying to attempt to get it to work without the voltage feedback–DON'T!All you will do if you attempt this is very rapidly destroy replacement MOSFETs/switching transistors in milliseconds because you'll prevent the thyristor switching on to discharge the MOSFET gate charge at the switch–off point in each operation cycle – the reason is that when the MOSFET drain current reaches a high enough point to saturate the transformer core, the induced voltage from the feedback winding that normally swings negative to turn off the MOSFET/transistor pair is prevented from being developed by transformer saturation, resulting in the devices being left turned on across the rectified mains h.t. supply, and they'll go bang, spectacularly!The control regulation works by using the opto to sense when the output from the appropriate secondary of the transformer reaches the desired value set by the preset output control and the designed o/p voltage, the opto will then conduct sufficiently between the emitter and collector of it's photo–transistor to pass a gate trigger current into the gate/cathode junction of the thyristor, causing it to fire, which then short–circuits the gate charge and the base current from the switching devices V6014 and V6018, which switch off and the primary current falls to zero. When the magnetic field in the windings of the supply transformer has collapsed, no further feedback voltage is supplied from the windings, however, a very small bleed current from the positive mains h.t. rail is then fed into the gate of V6018 and the base of V6014 via resistors R6002 and R6003, causing the switching devices to commence to conduct, and a rising current flows in the primary of the power supply transformer, producing a gradually rising positive voltage across the feedback winding again, until the point is reached where the opto H6001 starts to conduct again, and the cycle repeats with the thyristor firing as before!It's never necessary to attempt to run this design of self–oscillating power–supply open loop – if the transistors, thyristor and the feedback opto are all in good condition along with all the small components in the loop, the feedback loop is quite fast enough to take control of the switching stage before any damage to the transistors occurs!Properly repaired, these thyristor controlled blocking–oscillator supplies will come on quite safely with no need for any special precautions other than that provided by Philips for normal surge–limiting purposes!They are also capable of withstanding a short–term momentary output short–circuit, under these conditions the operating frequency drops to a very low value, causing a very obvious loud rattle or squealing noise from the power supply transformer, that immediately gives away an overload or short–circuit fault!The correct way to repair these type of power supply circuits is ONLY by checking each item meticulously against the maker's diagram for burnous, shorts or open–circuits as you go along!You can also use the plastic T0-92 case BRY55/BRY56 or the X0102DA thyristor in this circuit as the anode gate terminal is not used in this circuit – it is simply connected to the anode via R6027 to keep the junction held off!If you try one of the plastic–case thyristors, you want one advertised as "200V 0.8A fast switching sensitive–gate type", connect the anode lead to the Main FET gate/test point T45, the gate lead to the junction of R6010/R6011/R6012 and pin 4 of H6001, and the cathode to power supply H.T. – line (negative side of h.t. reservoir capacitors C6007/C6008) or common negative for the mains rectifier diodes.A common cause of failure of this type of self–oscillating power supply is the high–resistance feed from the positive rectified mains h.t. going open circuit or high resistance – this feed is provided by the two series resistors R6002 and R6003 – you can replace these with 390k standard values provided you fit ±1% tolerance components!If the chopper FET V6014 and/or the series switch transistor have been destroyed, you will need to source the correct replacement devices for this circuit (eBay) and check carefully all the small diodes and resistors around these two transistors against the diagram, replacing any damaged or open/circuit items.The LED part of the opto–coupler H6001 can go low–emission to the point where the control is no longer effective to control the h.t. output from the power supply, and it will try and increase the drive more and more to try and restore the missing feedback until something goes bang, but replacement with a new one will eliminate any doubt on that score!As long as you use the correct transistors for V6014 and V6018, take care over replacement of the thyristor V6006 with the exact type or a suitable replacement of the type I suggest, and pay careful attention to all the smaller components throughout the primary circuit, you will be rewarded with success – I have repaired many hundreds of monitors and other items of equipment using this type of design over a good few years!Don't forget, you MUST also replace all the Electrolytic Capacitors on the output side of the power supply transformer and the smaller capacitors in the primary side of the power supply once you have replaced all the damaged components!Chris Williams

author: srb1954
author_rank: Super Contributor
timestamp: October 23, 2020, 11:39:54 pm
content: Quote from: gkmaia on October 23, 2020, 09:43:58 amI checked the circuit diagram for my PM3394 scope and it has an almost identical PSU circuit except that it uses a BRY62 silicon controlled switch in place of the BRY39. The specs of these two devices look quite similar so you may be able to use the BRY62 as a replacement for the BRY39. It will require some bodge wires as the BRY62 is in a surface mount SOT143B package.Another interesting thing is that my Philips databook has two entries for the BRY39. In one listing it is described and characterised as a programmable unijunction transistor while the other listing describes and characterises it as a silicon controlled switch. In the scope PSU circuit I believe that they are using it as a silicon controlled switch.

author: gkmaia
author_rank: Frequent Contributor
timestamp: October 24, 2020, 11:12:10 am
content: Yes it is a Philips PM3055.Thanks for the tips. I feel so much of a beginner... electronics are so complicated. i wish i had the formal background as it would help to read these circuits better.I will give a good read to all your answers and see what i can learn from it

author: Ground_Loop
author_rank: Frequent Contributor
timestamp: October 24, 2020, 11:13:09 am
content: If you get stuck and really have to have a silicon controlled switch replacement I have an old frequency counter parts mule with about 50 of those in it. Let me know.

author: gkmaia
author_rank: Frequent Contributor
timestamp: October 25, 2020, 08:16:49 am
content: I have ordered some of the parts from china. Will wait till they arrive that will take a couple weeks.I will keep lifting and testing the other components.On that is badly burned out is R6001. I identified it as a thermistor 82ohms at 25C. Is that correct?https://nz.rs-online.com/web/p/thermistor-ics/1857851/possible replacement?As the thing is a complete carnage and blows fuses one after the other I cant even scope it anymore. And if what you said is true, if opto is faulty or one of the feedback transistors the thing will keep blowing.There is not really troubleshooting on this one. But taking it pretty much apart and testing one by one and only turning it on if sure all components are fine.So I will test each of these components.

author: Yansi
author_rank: Super Contributor
timestamp: October 25, 2020, 09:58:54 am
content: https://www.aliexpress.com/wholesale?catId=0&initiative_id=SB_20201025025832&SearchText=BRY39