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Can anyone on this forum measure the value of resistance between 2 and 5 pins of his working T2 Transformer? This is Apple Lisa PSU 120 VAC, 60 Hz, 1.2 Amp, 150W. Thanks

Hello all. I am trying to fix one of my problematic Apple Lisa PSU 120 VAC, 60 Hz, 1.2 Amp, 150W which isn't working. First thing that came to my notice is a resistance of the Transformer (T2 in the attached schema). I have compared it with the other working PSU 1.2 AMP but dedicated for...

Hi stepleton, I will try to gather this info as we did a lot of investigations before... But..I got something interesting that can have impact on all. Except all those previous investigations I managed to get the same status of the behavior on good board as on bad board. How?: When I was...

hi Stepleton, I did further investigation and compared CPU 68000 pin signals on both boards. I have only CPU 68000 connected (no ROMs, U8B and U8B) on both boards. On the bad board data lines pins D0-D15 has a HIGH +5v signal and look ok. This is probably because we see \READ signal HIGH on pin...

I am attaching measurements from U8C pin 11 and pin 9 - situation when 68000 CPU is in socket, but ROMs, U8B and U9B chips are removed from the good and bad board. Bad board U8C pin 11 and pin 9 (with CPU inserted and ROMs, U8B, U9B removed): Good board U8C pin 11 and pin 9 (with CPU...

Hi Stepleton, Thanks for answering on the lats post. I think U8C is good, because I see the same (pulsing) signal on pin 9 (it is output Y) as on pin 11 (input A from the function table). I also don't believe that IC tester could be wrong for such easy chip. When I got removed chips on bad...

Hi stepleton, Thank you for the answers and next ideas. I will strart from answering to your questions Yes, I have breadboard. I don't have signal generator. I am using the same Lisa and same power supply every time. I just swap CPU boards in it. Right now I have socketed (except CPU 68000...

Hi Stepleton, Thank you for the next advice. Below are measurements of resistance on multimeter. Chips U8B/U9B are removed ,68000 CPU and boot ROMs removed too. Values of resistance: On the bad CPU board: the resistance between UA10 (pin 38) and ground ( the boot ROM ground pin 14 ): OL On...

I am also attaching good CPU board measured with scope RESET PIN 18 on CPU (CH1) and PIN 11 UA16 (CH2) on U9B.

Hi stepleton. You wrote: I installed good board CPU 68000 to the bad board and checked UA9-UA16 once again. The situation with pins values is the same, but I verified that I pasted wrong image in my post regarding "RESET PIN 18 on CPU (CH1) and PIN 11 UA12 (CH2) on U8B". It should be...

Hi Stepleton, Thank you very much for reply. These are very helpful advices and I really appreciate it and that you can share with me. You are amazing! Before I reply to your answer let me explain what I did earlier today and share with you. Then I will reply to your post. The UA9-UA16 signals...

Hi Stepleton, Thank you very much for reply. These are very helpful advices and I really appreciate it and that you can share with me. You are amazing! Before I reply to your answer let me explain what I did earlier today and share with you. Then I will reply to your post. The UA9-UA16 signals...

Hi Stepleton, I did further investigations. Configuration now is: Good board and bad board without U8B and U9B and 2 ROMS (U13D and U14D ) chips connected. I measured all pins on U8B and U9B and they are looking pretty the same. I measured all pins on U13D and U14D and we have a difference. On...

I also removed both ROMs and U8B and U9B on the good board to check UA9-UA16 pins activity, and I see there good activity with +5V signals (pulsing) On the bad board without ROMs and U8B and U9B connected I don't see pulsing. Very interesting.

Hi Stepleton, U8B and U9B are good. So it means my IC tester won't lie:) I desoldered them and swapped on the good CPU board. Both are working and CPU board is booting.

Apologize for an error in previous post. Of course screens with values when U8B and U9B are removed (UA8 and UA9).

hi stepleton, I removed U8B and U9B (desoldered them) and measured UA9-UA16 pins on the sockets. I think that 74F283's are ok (but I will be 100% sure if I swap them with ones from good board). But please see below screens from scope and please let me know what you think. Meanwhile I desoldered...

Hi Stepleton, Thanks for interesting information.Your knowledge is amazing. I will check those U8B and U9B ICs - desolder. They are soldered. to the board, so I can desolder them again from board and swap with the other ones from workin board. I will also measure pins on the socket when they...

I am still wondering what might be the cause of those LOW pulses on CPU \RESET pin occurring regularly (yellow CH1 on scope). Those pulses are seen on U8B, U9B IC's and almost on every measurement I sent on CH2. I don't think U8B and U9B are bad. I checked them on IC tester and based on the...

Hi Stepleton, Thank for reply. Regarding \HALT pin on CPU it is static HIGH, no pulses. I am sharing also images from U9B of all pins. Yellow pin is CPU RESET pin: PIN 1 U9B: PIN 2 U9B: PIN 3 U9B: PIN 4 U9B: PIN 5 U9B: PIN 6 U9B: PIN 7 U9B: PIN 8 U9B: PIN 9 U9B: PIN 10 U9B: PIN...