Replacing old SCR's - Page 1
Forum section: electronics / projects

author: desertrout
author_rank: Contributor
timestamp: November 16, 2020, 03:11:28 pm
content: 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?

author: bdunham7
author_rank: Super Contributor
timestamp: November 16, 2020, 03:23:19 pm
content: Can you post a schematic of the circuit that it is in?

author: desertrout
author_rank: Contributor
timestamp: November 16, 2020, 05:26:33 pm
content: 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...

author: akimpowerscr
author_rank: Regular Contributor
timestamp: November 16, 2020, 05:44:06 pm
content: 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.

author: David Hess
author_rank: Super Contributor
timestamp: November 16, 2020, 06:03:02 pm
content: Quote from: akimpowerscr on November 16, 2020, 05:44:06 pmExactly, 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.

author: Doctorandus_P
author_rank: Super Contributor
timestamp: November 16, 2020, 06:31:34 pm
content: 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.

author: David Hess
author_rank: Super Contributor
timestamp: November 16, 2020, 07:24:54 pm
content: Quote from: Doctorandus_P on November 16, 2020, 06:31:34 pmIt 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.

author: akimpowerscr
author_rank: Regular Contributor
timestamp: November 16, 2020, 08:14:23 pm
content: 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

author: desertrout
author_rank: Contributor
timestamp: November 16, 2020, 09:45:47 pm
content: 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.

author: akimpowerscr
author_rank: Regular Contributor
timestamp: November 17, 2020, 06:30:13 am
content: QuoteFast thyristor technology is absolete and even for power inverters it has become difficult to find spare parts.I believe that you have no chance to find any other alternative than those given to you in this topic.But if you feel like wasting your time, it's your right.Buy 10 x 2N3050, try them in the power supply, some will probably work, some will not.I found one: BR103 from Siemens.https://www.ebay.de/itm/5x-30V-0-8A-Thyristor-BR103-Siemens-Halske/281011512080?epid=1169291962&hash=item416d976310:g:-AUAAOxyZqhRiQic

author: desertrout
author_rank: Contributor
timestamp: November 17, 2020, 08:39:02 pm
content: 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.

author: akimpowerscr
author_rank: Regular Contributor
timestamp: November 17, 2020, 11:09:49 pm
content: No way......ECG5589 is a thyristor of350ANTE5400 is not a fast scr, it will never work. (Tq is not even specified in the data sheet!)

author: desertrout
author_rank: Contributor
timestamp: November 18, 2020, 05:16:39 am
content: 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?

author: akimpowerscr
author_rank: Regular Contributor
timestamp: November 18, 2020, 08:49:59 am
content: 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 50µsMain'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 IGBTsFast thyristors are absolete technology, which is why they are hard to find because they have not been manufactured for a long time.

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: November 18, 2020, 01:25:45 pm
content: Quote from: akimpowerscr on November 18, 2020, 08:49:59 amI think you mean "obsolete".

author: akimpowerscr
author_rank: Regular Contributor
timestamp: November 18, 2020, 01:52:20 pm
content: Yes indeed, it is a google translation errorI am correcting in my 2 previous posts.Thanks for this correction.

author: mag_therm
author_rank: Frequent Contributor
timestamp: November 18, 2020, 05:11:26 pm
content: 2N1595 : TO39 1.6 A 50 V tq=10 usec typI saw some available on surplus in USA and UK.

author: desertrout
author_rank: Contributor
timestamp: November 18, 2020, 05:57:17 pm
content: Quote from: akimpowerscr on November 18, 2020, 08:49:59 amOK - thank you. I'm a new hobbyist, and your clarifications are very helpful

author: akimpowerscr
author_rank: Regular Contributor
timestamp: November 18, 2020, 07:21:44 pm
content: For more informations about turn off time of scr, see page 30, 31 and 32 : 3.4.2.4 turn off time tqhttps://www.infineon.com/dgdl/Infineon-AN20012_01_Bipolar_Technical_Information-ApplicationNotes-v01_00-EN.pdf?fileId=db3a304412b407950112b40ec42b126a

author: desertrout
author_rank: Contributor
timestamp: November 18, 2020, 08:29:28 pm
content: Quote from: mag_therm on November 18, 2020, 05:11:26 pmYeah, the 2N5060 has the same tq... apparently not fast enough

author: mag_therm
author_rank: Frequent Contributor
timestamp: November 19, 2020, 01:19:52 am
content: Quote from: desertrout on November 18, 2020, 08:29:28 pmI bet you will not find, ever made, a faster small scr with published tq <= 10 usec

author: akimpowerscr
author_rank: Regular Contributor
timestamp: November 19, 2020, 01:57:41 am
content: Quote from: mag_therm on November 19, 2020, 01:19:52 amYou loose: BR103 from Siemens has a published tq<6µsDatasheet in one of my previous posts.

author: desertrout
author_rank: Contributor
timestamp: November 19, 2020, 09:27:53 pm
content: Quote from: mag_therm on November 19, 2020, 01:19:52 amAnd the OE part E0122YA has a tq MAX of 10us

author: David Hess
author_rank: Super Contributor
timestamp: November 20, 2020, 12:37:46 am
content: Quote from: akimpowerscr on November 16, 2020, 08:14:23 pmTektronix used it also and not just for power conversion. This might look familiar:https://en.wikipedia.org/wiki/Blocking_oscillator

author: desertrout
author_rank: Contributor
timestamp: November 21, 2020, 06:59:59 pm
content: Quote from: akimpowerscr on November 18, 2020, 07:21:44 pmThank you. I also was looking at this document, which suggests the turn off capability of an SCR can be improved in various ways, including adding a heatsink (not possibly in this case), or a low RGKresistor (see page 19). Are any of these possibilities in the circuit I'm working with?

author: David Hess
author_rank: Super Contributor
timestamp: November 21, 2020, 11:12:28 pm
content: Quote from: desertrout on November 21, 2020, 06:59:59 pmSCRs normally include the gate shunt resistor internally as part of the construction which serves to remove charge over the entire gate area. An external resistor only connects to the gate at one spot and is less effective. Sensitive gate SCRs lack this internal shunt resistance.An SCR can be made from a PNP and NPN transistor and this allows access to the internal nodes allowing the performance to be tailored. I have never tried this but I think a pair of schottky diodes could be included to Baker clamp the transistors considerably improving turn-off speed.

author: akimpowerscr
author_rank: Regular Contributor
timestamp: November 22, 2020, 09:14:41 am
content: How many fast thyristors equivalent to the E0102YA do you need ?There are 4 more BR103 Fast Thyristors available at 4.99 € / pc on ebay, why don't you buy them?(see link in my previous post)If you are looking for a long term supply solution, you will not find it because of fast low current thyristors, it is not manufactured any more for a long time.

author: desertrout
author_rank: Contributor
timestamp: November 23, 2020, 02:04:31 pm
content: I did buy 5 of the BR103's from eBay for my immediate and future needs (should be arriving soon so I can verify they'll work), but in the future others and I will probably need a solution for when these old fast SCR's are simply no longer available, and that's what I'm curious about. David Hess's idea of using a couple of bipolar transistors and some resistors to 'make' an SCR is intriguing, or something like this which does something similar, using a modern replacement for the E1022YA then modifies the circuit with an NPN transistor, a Schottky and some passives:https://hackaday.io/project/168100-fat-macintosh-repair/details... But it would require an oscilloscope for specifics so this is all academic at this point.

author: akimpowerscr
author_rank: Regular Contributor
timestamp: November 23, 2020, 02:42:10 pm
content: You can also select 2N3050, trying them in circuit to see if the power supply works or not.No need of an oscilloscope to do this.

author: desertrout
author_rank: Contributor
timestamp: November 23, 2020, 04:14:14 pm
content: Quote from: akimpowerscr on November 23, 2020, 02:42:10 pmPerhaps an ignorant question, but what do you mean by 2N3050? The only info I see is for the 2N3055 transistors I've seen in amplifiers...?

author: akimpowerscr
author_rank: Regular Contributor
timestamp: November 23, 2020, 06:31:44 pm
content: Sorry, 2N5060

author: desertrout
author_rank: Contributor
timestamp: November 23, 2020, 08:21:34 pm
content: Ah lol that makes more sense

author: akimpowerscr
author_rank: Regular Contributor
timestamp: November 23, 2020, 09:22:58 pm
content: This is the kind of mistake that happens when you do two things at the same time, responding on the forum and having a conversation on the phone.Responding to a forum takes a lot of time, it's volunteering, it is difficult to devote yourself to it exclusively and full time, some topic starters often forget it.

author: desertrout
author_rank: Contributor
timestamp: November 24, 2020, 12:59:31 am
content: I, for one, appreciate it. Cheers.

author: desertrout
author_rank: Contributor
timestamp: December 07, 2020, 10:15:23 pm
content: Just to tie a bow on this, I've tested the BR103 in circuit and it works. Thanks everyone. Now to design a fast SCR replacement with modern components....