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Macintosh Plus Analog Board Q12 replacement
Posted by: macalle69 on 2017-02-25 10:42:52 Hello after burning i'm looking for a replacement of SCR E0122 YA 8 located in Q12 international , i founded in the forum a discussion in which suggested replacement with equivalent SCR 2N5060 , i try with it but does not work. Any suggestion , or somebody has original spare parts ?
Posted by: techknight on 2017-02-25 13:52:37 There was another thread on this somewhere and turns out that this part is pretty picky, it wont go into regulation with modern substitutes.
Posted by: macalle69 on 2017-02-26 02:17:01 There was another thread on this somewhere and turns out that this part is pretty picky, it wont go into regulation with modern substitutes. Hi Tech! Yes you're right, unfortunately I've tried with a modern 2N5060, apparently with the same features but it does not work properly
Posted by: techknight on 2017-02-26 04:07:12 Well modern substitutes have a reverse pinout as well. Do keep this in mind.
Posted by: Ferrix97 on 2017-02-26 11:37:30 There was another thread on this somewhere and turns out that this part is pretty picky, it wont go into regulation with modern substitutes. Here it is: https://68kmla.org/forums/index.php?/topic/26604-macintosh-128k-issues/page-2
Posted by: macalle69 on 2017-02-26 12:06:40 May the Force be with you Ferrix!
Posted by: marcelv on 2018-02-11 13:43:37 Am also looking for a replacement for the E0122YA _ _ \| x \| \|_ _\| \| \| \| \| \| \| 1 2 3 E0122YA (K G A) tested the foillowing replacements: BT169D (K G A) flupping set P0102DA (K G A) flupping set BRX49 (A G K)reverse! mac starts but is not stable According to the other post, it may be possible to tweak the power supply (alter some resistors) to accept the replacement. Think it's R50 but can someone let me know and the value to change it to? Altered the schematic from Larry Pina's book to the international version of the analog board. R45 390 R46 4,7 R47 1K R48 39 R49 1,5 R50 2k2 R51 220 R53 1,2 R54 15 R55 33k C42 470uF C45 470uF Q10 2SC3153 BCE Q11 2N3906 EBC Q12 E0122YA KGA
Posted by: techknight on 2018-02-11 16:24:31 I dont understand the early circuit topology enough to attempt to modify the design. I tried giving some input on this awhile back with Ferrix but I dont think it went anywhere honestly. You have to think, Switching power supplies were still in their infancy when this circuit was designed. Only thing the SCR can do is crowbar. once it latches, it hangs up until zero-cross. or the voltage completely depletes. Not to mention the schematic is drawn in such a weird uncommon way for todays standards to understand. It almost has to be re-drawn to understand the circuit better.
Posted by: Ferrix97 on 2018-02-12 02:42:50 The best thing to do is to try a bunch of BRX4x, It took me ages to find a working replacement. Best thing is to order an old part manufactured in the late 80s-90s and try that. Newer ones will not work.
Posted by: marcelv on 2018-02-12 13:37:20 Thanks for your replies. Put a 10K potmeter in place of R50, the mac is stable at 1K, so I replaced R50 with a 1K resistor. Problem is I have very little regulation on RPx to adjust the 5V, voltages are 5.2V and 12.35V Mac is working ok but don't know if this is the best solution.
Posted by: Ferrix97 on 2018-02-12 13:42:58 5.2V and 12.35V are on the limit of acceptable, I'd usually stay a tiny bit lower (like 5.1V), either way that shouldn't cause any damage
Posted by: marcelv on 2018-02-12 14:07:24 Ok , changed R50 to 1K1 (2x 2K2 piggyback) Voltages are 5.1V and 12.25V Have to find the sweet spot... :mrgreen:
Posted by: marcelv on 2018-02-14 15:02:25 tried some other resistors, 1K5 is too much (unstable), 1K , voltages too high. 1K1 and 1K2 work this is using a BRX49, don't have other BRX4x to test. You have to regulate the 5V to get as close as possible to the desired 5V value, too high or too low => crowbar.. 🤔 Still looking for a beter solution...suggestions...
Posted by: macalle69 on 2018-02-15 04:39:54 Hi Marcel thanks a lot for your support ! Will try and update you meanwhile I solved the problem finding another working analog board .
Posted by: marcelv on 2018-02-20 12:59:35 Maybe the following can help to understand the circuit better, is part of the powersupply schematic does anyone have the schematics for the international version of the analog board?
Posted by: macalle69 on 2018-02-20 13:16:06 Thanks a Lot Marcel Fixed following your suggestions!
Posted by: techknight on 2018-02-20 14:37:37 With absolutely no details of what you meant by "fixed". Please elaborate for the others in this forum that could use this information. (like me 🙂
Posted by: macalle69 on 2018-02-20 16:43:00 Hi Techk telling the truth this fix I have done on an 120v (american analog board) I placed BRX 45 with 1K 1/4w in the central pin , this worked for my analog board
Posted by: techknight on 2018-02-21 15:07:01 Ah ok, so you added some resistance to the circuit.
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