Image Map Image Map
Page 2 of 9 FirstFirst 123456 ... LastLast
Results 11 to 20 of 89

Thread: Apple ii europlus

  1. #11
    Join Date
    May 2018
    Location
    Lancashire
    Posts
    158

    Default

    I was wondering if it's a slow blow, hence T2.5. I imagine it would be for this application.

    You can test rectifiers in circuit within reason, just one cap hiding a diode, others are fine, but I might whip it out to be sure.

    Question, seems to be some debate on running the psu with no load, some say it won't work, others say it's fine.

    Edit, good call on rectifier, what I was seeing measured in circuit was exactly what it shows out of circuit, one diode has gone short circuit, switching the fluke off diode still shows zero ohms from once AC leg to the negative terminal in both directions. Chicken or egg ?

    Need some more time now to check other input components before power up.

    This is fun. When I used to work on circuits of this age in the 80's, the parts were easy to get, now you have to spend a bit of time getting the old specs and comparing to new to make sure it's all covered

    There are quite a number of KBP cased rectifiers out there with different specs, so gone for a 210, 2A 1000v, 1.1 forward drop in a KBP case, should be ok.

    R1 checked and looks good.
    Last edited by Gary C; July 8th, 2018 at 04:51 AM.

  2. #12
    Join Date
    Sep 2016
    Location
    Melbourne, Australia
    Posts
    627

    Default

    Also check the main switching transistor, it may have been what triggered the whole sequence of events.
    If Q1 looks good then I'd fit the new bridge and fuse, recap and fire it up with no load.

    2A/1000v is the spec for the KBP10. 1000v is probably more than needed. The KBP206 (2A/600V) are also common on ebay at 10 for a $1

    As to the PSU under load debate, anyone that tells you they dont work without a load has never tried it. I can assure you the run just fine with no load. I've repaired more than 30 of then in the last 3 years and every single one was initially tested with no load. Only when I am 100% satisfied the supply can maintain its voltage without going high do I test them under load. A switch mode power supply with a regulation fault tends to go over voltage and triggers the crowbar protection. If it can maintain its voltage with no load then its unlikely to go over voltage with a load.

  3. #13
    Join Date
    May 2018
    Location
    Lancashire
    Posts
    158

    Default

    Will check Q1 too, thanks for the advice. Will try it no load first (I couldn't see how it wouldn't work, but hey ho).

    Only bought it (and others) for the fun of fixing them.

  4. #14
    Join Date
    May 2018
    Location
    Lancashire
    Posts
    158

    Default

    Well, new rectifier fitted and DC supply present but PSU not working.

    Q1 & Q2 appear ok.

    So while the circuit diagram on page one is generally ok, it doesnt include the details of T2 & T3 and there seems to be some anomolies. A diagram from applebox (http://www.appleii-box.de/D04_allabotpowersupplies.htm) giving a more detailed circuit and expected signals seems to disagree with the connections (specifically Q2 collector seems to be only connected to the coil in T2 in the applebox diagram where as the diagram on page 1 suggests connections between C9 & C8 and T2)

    is there a definative, verified, detailed diagram of an AA11040C (or even just a B) ?

    So next candidate diode? so will take them out one at a time, along with Q1 & Q2 to fully test out of circuit, but I also need to check the coil continuity and cant find a definative drawing.

  5. #15
    Join Date
    May 2018
    Location
    Lancashire
    Posts
    158

    Default

    My mistake, the test diagram I found was for the very similar Apple III psu. Still, it's hard to test using the widely available drawing for an a11040b when the internals of T2 aren't shown.

    So, anyone, what forms the oscillator?, C7 is given as setting the frequency of the oscillator, but its an electrolytic and wouldn't like + & - Ve of a normal LC tank ?

    What forms the parallel LC that Q1 maintains ? Also noticed that R25 is missing, read another thread where this was the same, when replaced and the psu sprang into life. R25 sit's parallel with R24 and I can see no reason why it's not there. The legs are present but under close inspection they don't look snipped but there are no debris in the case to suggest it popped. Odd.

    Ageing brain gradually starting to work but needs a little help to change gear.
    Last edited by Gary C; July 13th, 2018 at 08:24 AM.

  6. #16
    Join Date
    Sep 2016
    Location
    Melbourne, Australia
    Posts
    627

    Default

    Replace C7, it is often the cause of the symptom you have. The other likely culprit is the small feedback transformer, one of the windings goes OC. Its easy to test in circuit, if one set of windings reads 68 ohms in circuit then it has gone OC. If it has let me know and I'll tell how I fix them.

    R25 is one of the resistors used to adjust the 5v level. depending on the voltages the factory would cut out a resistor to set the voltage

  7. #17
    Join Date
    May 2018
    Location
    Lancashire
    Posts
    158

    Default

    Thanks

    Already swapped C7 and Q1 has two good PN junctions so that looks ok. Will check Q2 out of circuit next.

    Will need to have a good look with the scope on Monday when I actually have a day off.

    Just trying to work out which bits form the LC oscillator.

  8. #18

    Default

    The back of this pdf has some theory how they operate. It covers several models.
    ftp://ftp.apple.asimov.net/pub/apple...lies_Aug82.pdf

    Larry G

  9. #19
    Join Date
    Sep 2016
    Location
    Melbourne, Australia
    Posts
    627

    Default

    It could be the small signal transistors and on a rare occasion and open circuit resistor on the primary side. However the most likely problem is that feedback transformer, 70% of the faults I get that are not fixed by a recap are that transformer.
    14940108_1318136234883532_2505776855320786254_o.jpg

    If it faulty you will read about 68 ohms across these terminals in circuit. To fix it wind on 30-35 turns of enameled copper wire in the same direction as the original windings and terminate the ends on the terminals marked. I've found that 30-35 gives about an output voltage close enough to spec that I dont have to mess about with the adjustment resistors.

    Quote Originally Posted by Gary C View Post
    Thanks

    Already swapped C7 and Q1 has two good PN junctions so that looks ok. Will check Q2 out of circuit next.

    Will need to have a good look with the scope on Monday when I actually have a day off.

    Just trying to work out which bits form the LC oscillator.

  10. #20
    Join Date
    May 2018
    Location
    Lancashire
    Posts
    158

    Default

    Cheers

    Will check. Been a long time since I've had to rewind a coil.

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •