In the Macintosh restoration community, we're finding that some components are getting difficult to replace. One in particular is a 0.8A/30V/200uA fast SCR that has several old part #'s: E0102YA, E0122, CR400Y... but none of these are in production. The modern equivalent is the 2N5060 - it looks the same on paper - but it doesn't work. (In this case, it's part of a 'kickstarting' circuit of a switching power supply, the 2N5060 results in crowbarring, the E0102/E0122 don't)
My question is why would that be?
Here's the datasheet for the E1020YA:
https://datasheet.datasheetarchive.com/originals/scans/Scans-007/Scans-00148351.pdfHere's the datasheet for the 2N5060:
https://my.centralsemi.com/datasheets/2N5060_SERIES.PDFOne theory is that the gate current trigger test conditions are different for each... that the E0102YA tested at 10Ohms, the 2N5060 was tested at 100Ohms, a magnitude difference... but I can't find a datasheet to confirm that.
What am I missing?
Can you post a schematic of the circuit that it is in?
Unfortunately there's no official schematic for this circuit... it's for a Macintosh 128k / 512k/ Plus analog board, which includes a switching power supply and the video sweep circuit all on the same board. Some folks have attempted to reverse-engineer schematics... I've attached a screenshot from repair guide (
https://vintageapple.org/gamba2/images/plus_analog.PDF) that isolates the part of the circuit where the E0122 (at Q10) resides...
Try to select 2N3050 for the lowest Tq possible.
tq typical is 10µs.
Tq of E0102YA is not specified on the datasheet but must be lower than that.
Try to select 2N3050 for the lowest Tq possible.
tq typical is 10µs.
Exactly, going by the datasheets, the 2N3050 does not turn off as quickly as the original "fast" SCR. The E0102 is 10 microseconds maximum while the 2N3050 is 10 microseconds typical, so could be much slower.
If I was desperate, I might replace the SCR with a pair of fast high voltage bipolar transistors and some passives in the SCR configuration.
If you can't find a faster SCR, then maybe de sensitizing the crowbar circuit a bit is a viable option?
But instead of changing random stuff, modifications like this beg for some serious measurements with a scope to diagnose what is really happening.
If you can't find a faster SCR, then maybe de sensitizing the crowbar circuit a bit is a viable option?
It is not a crowbar circuit exactly. Other switching converters based on the blocking oscillator use a transistor switch in place of that SCR to do the same thing. That is duty cycle modulate the blocking oscillator.
It is a self-oscillating flyback converter that works on the same principle as some Philips oscilloscope power supplies.
When the current in transistor Q11 reaches around 1A, transistor Q9 conducts and triggers thyristor Q10 which blocks Q11.
Thyristor Q10 must have a very short extinction time (tq) so as not to remain in conduction at the end of the cycle when Q11 must again enter into conduction.
Although the BRY39 used as a fast thyristor in Philips power supplies is also difficult to find, but less so than the E0122, it could replace the E0122 with a simple modification.
https://www.eevblog.com/forum/repair/replacement-for-an-old-bry39-programmable-unijunction-transistor/msg3292608/#msg3292608
Thanks everyone. What you're all saying makes sense.
There is in fact an official schematic - I just found it this afternoon, so I've attached here in case there's more to say. I'll continue to look for a faster SCR with the right values.
Of note is also this post (
https://hackaday.io/project/168100-fat-macintosh-repair/details) where the author made some observations of the system with a scope and made some alterations that seem to hold - for curiosity's sake.
I've also found on ebay NOS ECG5589's and NTE5400's that considered replacements. But this of course is a short term win. You are correct, ultimately, once this old stock has dried up, other solutions will need to be found.
No way......
ECG5589 is a thyristor of
350A NTE5400 is not a fast scr, it will never work. (Tq is not even specified in the data sheet!)
Mis-type - I meant SK3950, but it is billed as a NTE5400 replacement. How do you know for sure the NTE5400 will not work - is the fact that tq is not on the datasheet proof?
Tq (or toff) is an essential parameter of a fast thyristor.
It is obvious that if this parameter is not even informed in the datasheet, it is not a fast thyristor.
Fast thyristors (including power thyristors) have a tq (or toff) generally between 5 and 50µs
Main's thyristors generally have a tq between 50 and 150µS.
Fast thyristors had been developed for inverters.
In this application, they were first replaced by GTOs (gate turn off thyristors, which was not a good technology) and they are now replaced by mosfets or IGBTs
Fast thyristors are absolete technology, which is why they are hard to find because they have not been manufactured for a long time.
Fast thyristors are absolute technology, which is why they are hard to find because they have not been manufactured for a long time.
I think you mean "obsolete".
Yes indeed, it is a google translation error
I am correcting in my 2 previous posts.
Thanks for this correction.
2N1595 : TO39 1.6 A 50 V tq=10 usec typ
I saw some available on surplus in USA and UK.
It is obvious that if this parameter is not even informed in the datasheet, it is not a fast thyristor.
OK - thank you. I'm a new hobbyist, and your clarifications are very helpful
2N1595 : TO39 1.6 A 50 V tq=10 usec typ
I saw some available on surplus in USA and UK.
Yeah, the 2N5060 has the same tq... apparently not fast enough
Yeah, the 2N5060 has the same tq... apparently not fast enough
I bet you will not find, ever made, a faster small scr with published tq <= 10 usec
Yeah, the 2N5060 has the same tq... apparently not fast enough
I bet you will not find, ever made, a faster small scr with published tq <= 10 usec
You loose: BR103 from Siemens has a published tq<
6µsDatasheet in one of my previous posts.
Yeah, the 2N5060 has the same tq... apparently not fast enough
I bet you will not find, ever made, a faster small scr with published tq <= 10 usec
And the OE part E0122YA has a tq MAX of 10us
It is a self-oscillating flyback converter that works on the same principle as some Philips oscilloscope power supplies.
Tektronix used it also and not just for power conversion. This might look familiar:
https://en.wikipedia.org/wiki/Blocking_oscillator