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485 power supply switching transistors Q1834 and Q1844

 

Have an 485 with both Q1834 and Q1844 shorted. So there may (probably?) be other issues. But at least will need these two replaced. I'd like help identifying current replacements.

They are 151-0368-00. Apparently oem were MJ13015 long obsolete. Though Sphere currently shows 2 new 2 used. I do not find a datasheet for MJ13015. Old threads mention a couple parts but the only thing that seemed 100% to work was BUX48A but it also is obsolete or at least I can't find it. The datasheet I find for BUX48A looks as if it was overkill for the application which might push any failure farther into the box.??

Thanks
 

John
The MJ13015 ( Looks like a? Motorola part #) crosses to NTE2319
DUX48A crosses to a NTE386, the data sheets are very similar.

Both of the NTE parts have data sheets on the NTE web site, and show inventory and several distributors

go here:?

Then enter your OEM part number? in the upper left hand corner in the "cross reference" search box to see the data sheets. Both parts are TO3 / 175W / 800V Vce /15A

While I have not used these particular parts I have had good luck on many occasions using NTE crossed parts. . Both of the NTE parts are also available on Evil-Bay and that retailer named after a river in South America. Sphere is always a good bet and very trustworthy, No affiliation to any of the above...? just satisfied customer

-DC
manuals@...

On 4/2/2018 6:29 AM, John Brown wrote:
Have an 485 with both Q1834 and Q1844 shorted. So there may (probably?) be other issues. But at least will need these two replaced. I'd like help identifying current replacements.

They are 151-0368-00. Apparently oem were MJ13015 long obsolete. Though Sphere currently shows 2 new 2 used. I do not find a datasheet for MJ13015. Old threads mention a couple parts but the only thing that seemed 100% to work was BUX48A but it also is obsolete or at least I can't find it. The datasheet I find for BUX48A looks as if it was overkill for the application which might push any failure farther into the box.??

Thanks


--
Dave
Manuals@...
www.ArtekManuals.com
 

Hi John:

My Tek Common Design Parts Catalog shows the Jedec part number as 2N6308. There are probably NTE replacements for the 2N6308. You should also replace all the associated diodes around the switching transistors with 1N4007 ones. They are rated 1KV at 1A, an overkill but a big safety margin. With an oscillator at about 21KHz test the resonant circuit components L1835 and C1835, they should display minimum impedance at resonance. Unsolder the anode end of CR1848 and go between TP1835 and pin 2 of P1960 to make this test. If resonance cannot be achieved at about 21KHz then one component of the resonant circuit is defective and a severe impedance mismatch exists between the power inverter circuit and T1960.

Reed Dickinson

On 4/2/2018 3:29 AM, John Brown wrote:
Have an 485 with both Q1834 and Q1844 shorted. So there may (probably?) be other issues. But at least will need these two replaced. I'd like help identifying current replacements.

They are 151-0368-00. Apparently oem were MJ13015 long obsolete. Though Sphere currently shows 2 new 2 used. I do not find a datasheet for MJ13015. Old threads mention a couple parts but the only thing that seemed 100% to work was BUX48A but it also is obsolete or at least I can't find it. The datasheet I find for BUX48A looks as if it was overkill for the application which might push any failure farther into the box.??

Thanks
 

On Mon, Apr 2, 2018 at 03:29 am, John Brown wrote:


So there may (probably?) be other issues.
You can almost bet on it. I detest that type of power supply when it is self oscillating, but they are efficient when they work.

So either the transistors are underdriven or overloaded. There is no snubber capacitance to be at fault, the circuit really doesn't have an inductive kick like single ended ones.

If it proves to be the drive, hope it is C 1841/1834 or the resistors across them. In fact they warrant a quick check before going to other trouble. And the load on CR 1832/1833, or the diodes themselves.

(one of my JURB techniques if not)

I would find an audio amp and feed T 1960 with it. Whichever winding you choose to backfeed depends on the power of the amp. About a 3 KHz square wave should drive it well enough and probably won't destroy the amp. If you can't drive it to the full voltages they should at least be proportionately low. Watch that amp for heat buildup, they are not made for 3 KHz square waves, if current doesn't get it dv/dt could.

If you get proportional outputs from that side of the PS look at the drive. There isn't much to slow it down. (take that both ways :-)

I see the thing has current limiting but sometimes they sit there too long running into a short and go poof, maybe from heat if nothing else.

I see it senses beam current, HV current and the cathode of the CRT, but that isn't necessarily used for protection. I didn't read the theory of operation, if you can find the right section it might be worth a look.
 

On Mon, Apr 2, 2018 at 04:16 pm, Reed Dickinson wrote:


If resonance cannot be achieved at about 21KHz
It would be nice to able to really drive it at that frequency. My idea should work though. Part of the thing is to get enough voltage up to see if the CRT is shorted.
 

Hi, when I repaired my 7904 I used two BU208A with good result. I guess 485 and 7904 supplies are similar.
And it works fine.
G?ran
 

I want to thank EVERYONE. Wow. I'm operating above my pay-grade working on these and between the manual (theory of operation) and your suggestions I will be awhile understanding what's going on. At least a little bit. But then that's why I enjoy this it's a learning exercise. I have some specific tech questions but want to mull things over some more and will ask in a new thread with an appropriate subject.

I actually have two 485 both inop. Both blew fuses but the other stopped with replacement of the big caps; this one obviously is still not happy. I think I'm going to button this one up for now (I'm short on space) and focus on the other.

Just for future Googlers:

2N6308 is listed obsolete and not in stock at Digikey or Mouser; but TEDSS.com has them reasonable and they're all over eBay. TEDDS sometimes has stuff and I've had good service. I may get a handful cause they're cheap and apparently oem so how bad can they be.
BU208A is listed obsolete if at all and not in stock but also eBay and plentiful.

So thanks again. I'll jot this all down in the notebook and be back with questions on the 'at least it don't blow the fuse up' scope after more book study.
 

The 2N6545 (8 amp 125 watt) is the general purpose replacement for
transistors in that series and is still produced. These can probably
be found cheap somewhere.

I am not sure where you found the MJ13015 part number but I suspect
the 10 amp 150 watt Motorola part is basically the same thing with
some refinements and tighter specifications. Motorola had a habit of
producing parts like this to cater to specific applications. They
probably have an application note for it.

The 7000 mainframes through the 7904 use the 5 amp and 110 watt 2N6308
and the 7844 uses the -01 part which is graded for Toff > 3us for some
reason. I have not gotten to tracking down the later ones yet.

It will be important to make sure transistor failure was not caused
externally. Possibly this is just a case of one dying and taking the
other out.

On Mon, 02 Apr 2018 03:29:19 -0700, you wrote:

Have an 485 with both Q1834 and Q1844 shorted. So there may (probably?) be other issues. But at least will need these two replaced. I'd like help identifying current replacements.

They are 151-0368-00. Apparently oem were MJ13015 long obsolete. Though Sphere currently shows 2 new 2 used. I do not find a datasheet for MJ13015. Old threads mention a couple parts but the only thing that seemed 100% to work was BUX48A but it also is obsolete or at least I can't find it. The datasheet I find for BUX48A looks as if it was overkill for the application which might push any failure farther into the box.??

Thanks

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