68kMLA Classic Interface
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| Analog Board 610-010B Mac 512k - T2 8432 short. H7C1 | |
| Posted by: flowers on 2016-11-27 04:13:46 Hi there, I'm under a check/repair of an Analog board x a 512K; seems that the Flyback is gone and i already desoldered it, what appeared to me was that the system got the bong, black screen,hot capacitors C1and C2 ( measured are steel good) and shorted to ground as a lot of other components with the flyback on; desoldered it i see steel to ground restores R10 (5W 39 ohm) and R11 (1/4w 100 ohm) that make me link to the T2 seems to be also broken the component T2 labelled 906 8432 on top and H7C1 on the bottom side ( online i see it labeled on top 157-0039 in Mac Plus analog board) i'm not so in deep in such transformer, maybe i'm getting a wrong consideration... but the wire couple on the two sides do not get any resistance but result as shorted... at last i aspect that a resistance is present for the two filament coils ... i'm thinking that it is cooked with shorted coils.  Is there anyone that knows the parameters of it or can measure the value to understand what substitute i can found today ? Any suggestion is welcome, and if i'm wrong please let me know.. thank you Michele | |
| Posted by: techknight on 2016-11-27 07:04:19 you cant tell if that thing is shorted or not without a ring tester. All inductors appear to have a "DC Short". | |
| Posted by: flowers on 2016-11-27 07:18:01 ... yes thats true... so i have to go to put it back, switch on and check the output voltages. Maybe its only my fear before switch on this logic board with another flyback... getting into it with the multimeter i was thinking that a certain resistance has to be present by the Coil itself. | |
| Posted by: techknight on 2016-11-27 07:45:23 Not that coil, there is not enough turns to have a DC resistance a meter can measure. It has to be ring tested. | |
| Posted by: bibilit on 2016-11-28 07:48:56 Same problem here: https://68kmla.org/forums/index.php?/topic/28839-unusual-analog-board-problem-mac-128k-512k-plus/ | |
| Posted by: flowers on 2016-11-29 22:34:50 Yes bibilit, it seem to be the same/similar problem. I ordered the flyback as i realise to had no working spare ... i'll get it in the next weeks and i'll do a try; my doubt on T2 (01570039) remain and could be then needed to found a right replacement of it, i had no other analog board to get info into it, if someone can measure in a working logic board the voltages at the two side/coils and post that value here could be useful, and with informations of this component at last we have it here in this forum for who will need it as working unit ref. Asap i'll test the board first with a new working flyback; i'll be back here with good or not good problem solving, then i can see the next step, every good thought is welcome. 🙂 I checked other parts of the board but i didn't found at the moment other potential culprit, Q6 and Q3 where fine, i upgrade Q3 independently to BU406D for the next new flyback trial.  | |
| Posted by: flowers on 2016-12-24 05:09:15 i get into the analog board today... having some time to work on by these holiday 😉 . I received the flyback spare one week ago; mounted it the result is been .. PROBLEM SOLVED. So all stuff i mention above was linked to the dead Flyback that probably reach its honourable more then 30 years service 🙂 So techknight was right, and is definitively not an indication the voltages around the T2 and its coils; a ring tester is needed for that or nothing more then a short DC value can be found as i get; now i'm stimulated to get into an homemade ring tester ^_^ .. i'm looking around some ideas. My best wishes of a nice Christmas time for all of you here ^_^ and thanks for the support. | |
| Posted by: techknight on 2016-12-24 12:06:19 IF servicing these things is what your gonna do often, I recommend the AnaTek blue ring tester. I have one I bought as a kit and built it. Works great for shit like this. Just about every flyback I suspected was bad, ring tested bad. | |
| Posted by: flowers on 2016-12-26 01:32:37 Thank you techknight, i checked online this blue ring tester and i think to definitively go to get it in parts to assembly.. 🙂 | |
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