Compact Flyback Transformer: 157-6139?

[trag]

In my lackadaisical search for a source of flybacks for the compact Macs, I came across this part number. They list it as an Apple flyback transformer, but there is no other information listed (nor a datasheet) and the photo is one they use for dozens of other flybacks.

Anyone know if this part number (157-6139) indicates a usable substitute for the 157-0042 we all know and love?

I emailed the company and received zero response which would ordinarily cause me to resolve never to do business with them, but when someone might be the only remaining source for a part...

 

[wally]

http://www.dalbani.com/

They currently have a 157-0042B flyback in stock.

They also show a C version but currently out of stock.

 

[trag]

http://www.dalbani.com/They currently have a 157-0042B flyback in stock.

They also show a C version but currently out of stock.

Thanks, Wally. I've managed to miss finding them for the last several years. I still have a few flybacks in my parts supplies and I don't want to run down the supply for others. On the other hand, all these parts are at an age where sellers may scrap them without warning, so buy it now or never see it again is also a valid attitude. Hmmmm.

 

[wally]

Yes indeed. For example, MCM used to stock the one for the Mac, but best I can tell no longer.

 

[trag]

Any idea what the difference is between the 0042-B and the 0042-C?

Was the C the one that added the bleeder resistor?

 

[wally]

The simasimac page at

http://www.biwa.ne.jp/~shamada/fullmac/repairEng.html

has a nice chart of various flyback numbers and which have the bleeder. It appears that 157-0042 had the bleeder in all ABC versions. The numbers appear to be from Larry Pina Macintosh Repair and Upgrade Secrets 1990 page 95, with the addition of bleeder info from Appendix C/D and elsewhere. It looks like the B version was the recommended replacement in 1990. I know that the A version had a tendency to have herringbone pattern failures (Pina, Dead Mac Scrolls 1992 page 145) and he recommended the C version for replacements. Don't know what issues were addressed going from B to C. But I notice I have an A version on my spare reference analog board that was working just fine a few years ago, I would gladly use it as a donor to rescue one of my existing SE/30s if need arises. I'm sure C is better somehow, but a working A or B is a lot better than a paperweight. Elsewhere on the Internet I read today that the low cost of monitors has led to the collapse of the repair infrastructure and parts distributors for all but the most expensive monitors in the US. Cheaper to get a new one. This may explain the single digit prices for flybacks (presumably for smaller CRTs) from certain distributors while others hold out for $35 (presumably for giant CRTs).

 

[trag]

Ah, checking the chart that you referenced, I see that it was the -0026 which added the bleeder between the 'B' and 'C' revisions. That's probably where that memory came from.

Okay, well, I ordered ten of the 0042Bs, which should fulfill my personal needs unless I live a lot longer than people usually do.

I might email the company and ask them to contact me if they decide to scrap the remaining stock. Folks rarely remember to follow up on that kind of thing though.

And I'm already stocking reels of tantalum resistors for the Mac community... Still, it's tempting to stock up beyond my needs.

 

[stevep]

So will the -0047 work as a replacement for the -0026?

 

[wally]

According to Larry Pina (1990) Appendix C/D/E pages 333, 340, 344, the 157-0042B will replace all of the earlier models including the -0026, for the Macintosh Analog Board US Version, International Version, and on the Macintosh SE Analog Board (used on SE and SE/30). Pina's subsequent 1993 book page 55 mentions that flyback failure with -0042B and -0042C is relatively rare. So best I can tell from Pina, either the B or C part are excellent for repair purposes.

If you should decide to do a replacement, consider carefully Pina's recommendations to replace the switching transistor and the discrete diodes that connect directly to the flyback, to avoid the possible quick death of the replacement flyback :disapprove: when you apply power!

The 157-0047-A is another kind of part altogether, for which the answer is no. I believe it is a power transformer used on the International Version only, Pina (1990) page 340.

 

[stevep]

Thanks Wally!

Would you have the part numbers or board locations of these diodes and the transistor? The board I'm looking at is dated 1983 (820-0082B on the trace side, 630-0102 component side), and I think the transistor must be Q3 but I see 4 diodes that look to be directly connected to the flyback.

 

[wally]

Don't have that exact board for reference, and Pina says the reference designators do change between Mac US, Mac International, and SE|SE/30 versions. So perhaps you will have to do some reverse engineering to figure out your analogous designators. On the SE analog board Pina says change CR2, Q2, CR3, and CR5 to be safe. These parts are in places where if stuff goes wrong the current flow could be big.

CR2 MR854 anode grounded, cathode goes to flyback pin 2

Q2 BU406 collector goes to flyback pin 1 and the anode of CR4 which is not on Pina's recommend to change list.

CR3 MR854 cathode goes to flyback pin 3

CR5 1N4937 anode goes to flyback pin 8

The flyback pins are numbered 1 thru 8 counterclockwise from the solder side, and on the component side look for pin 1 designated in silkscreen. Pin 6 is a no connect.

In Tom Lee's Classic Mac Tech Docs v2.0 figure 10, these parts correspond to CR5, Q3, CR1, and CR10. Tom also says GI854 is same as MR854. The CR4 on the SE analog board corresponds to CR11 on Tom's figure 10.

You also might consider changing two electrolytics, if not all of them. On Tom Lee's figure 10, consider the infamous C1 if it has not already been upgraded to film, and also the capacitor with no reference designator (220uf/16V) that connects from the anode of CR1 to flyback pin 4. Both of these have to block DC and pass a respectable amount of AC current at the same time. They could be trouble also. Also C14 (22uf/50V): normally not much power, but if it shorts, not good.

Hope this helps

 

[trag]

It looks like Pina says you can use an MR824 in place of the GI854/MR854. It looks like they are 400V/5A vs. 600V/3A respectively.

 

[wally]

Right, I missed that. Furthermore, in Dead Mac Scrolls, page 147, he goes further than the 1990 book and says the MR824 is the preferred heavy duty replacement part if a GI854 part is failed shorted. I looked briefly at the datasheets and the 824 is definitely beefier, similar in reverse recovery speed, but has somewhat higher junction capacitance. But if Pina says no raster glitches have been observed using the MR824, maybe beefier is better...

 

[stevep]

Thanks guys for the info! My flybacks arrived today, so out comes the soldering iron

 

[stevep]

WooHoo....

Just powered up my repaired board and it works I am amazed to be quite honest.

A few adjustments to be made to centre the picture etc and glue the white backer card in place and it's done.

Happy New Year!

 

[trag]

Just powered up my repaired board and it works I am amazed to be quite honest.

A few adjustments to be made to centre the picture etc and glue the white backer card in place and it's done.

That's great.

BTW, Radio Shack used to carry the double side sticky foam that is used to put the white card in place. They probably still do carry it, but I don't want to claim that they do when it's been so long since I purchased any there. It comes in three or four inch long strips.

 

[stevep]

BTW, Radio Shack used to carry the double side sticky foam that is used to put the white card in place. They probably still do carry it, but I don't want to claim that they do when it's been so long since I purchased any there. It comes in three or four inch long strips.

I miss Radio Shack - here in Canada they are now called The Source, but they are just like any other electronics retailer now; mostly consumer stuff and very few parts and other supplies like they used to have.

 

[techknight]

Lets face it. We are a dying breed. ever since the electronics production has went overseas, the "electronics hobby/repair" as we know it is toast. Pretty soon we will be extinct except for china. lol.

I was born "gifted" in this area. (at least i think so.. hehe.) and have certifications and degrees in electronics. But, its a dying breed. Still no employment at least in my area, So i just became partners with a buddy of mine trying to run a computer/electronics repair business. which is struggling.

So its not surprising what radioshack has done. as theres hardly any market for it anymore, they move towards basic consumer crap which theres a booming market in as they moved away from the electronics hobbyist market which is dying off. no need for electronics hobbyists as the manufacturing, service and other related "jobs" required in that field are slowly going bye bye

 

[trag]

Well, they seem to be out of stock now. Sigh. I hope they didn't scrap the remainder with the new year or something. I hope they actually sold out.