No clock signal to the Shifter

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russellnash
Posts: 114
Joined: Fri Mar 26, 2021 2:46 pm

Re: No clock signal to the Shifter

Post by russellnash »

You shouldn't be worried about offending me, there is no such thing as causing it, only taking it. :D
I ask questions because I would like an answer and answers that are relevant and truthful are the best answers. I already know more now from your comments than I did before.
There is probably a good reason that you use an oscilloscope, otherwise you wouldn't use one. It is nice to have all the right stuff that you need. The reality is that people tend do all sorts of things without all the necessary tools and equipment. That is true from cooking in the kitchen to mixing concrete.
Thanks.
russellnash
Posts: 114
Joined: Fri Mar 26, 2021 2:46 pm

Re: No clock signal to the Shifter

Post by russellnash »

After I replaced L22, R86 and R91, which are the three components between Y2 and Y3 on the photo, the input and output of the Shifter both oscillate on the logic probe, at the MMU, GLUE and CPU etc.
russellnash
Posts: 114
Joined: Fri Mar 26, 2021 2:46 pm

Re: No clock signal to the Shifter

Post by russellnash »

With respect to the possibility of using either 2 or 6 chip TOS on this type of board I noticed something that got my attention. On the original 520ST schematic pin 22 OE of the TOS Roms is connected to UDS and LDS and also to the cartridge port. However, on the schematic for the 1040ST the TOS Roms are connected to ground with pin 22 via the A17 jumper. Is that correct that to run such a board with 6 chips they must no longer be connected to LDS and UDS?
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rubber_jonnie
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Re: No clock signal to the Shifter

Post by rubber_jonnie »

russellnash wrote: Wed Mar 27, 2024 12:33 pm With respect to the possibility of using either 2 or 6 chip TOS on this type of board I noticed something that got my attention. On the original 520ST schematic pin 22 OE of the TOS Roms is connected to UDS and LDS and also to the cartridge port. However, on the schematic for the 1040ST the TOS Roms are connected to ground with pin 22 via the A17 jumper. Is that correct that to run such a board with 6 chips they must no longer be connected to LDS and UDS?
I've converted several 2 chip boards to 6 chip and all I ever did was add the decoupling caps and change the jumper pads that set the ROM size.
Collector of many retro things!
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Approx 20 STs, including a 520 STM, 520 STFMs, 3x Mega ST, MSTE & 2x 32 Mhz boosted STEs
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russellnash
Posts: 114
Joined: Fri Mar 26, 2021 2:46 pm

Re: No clock signal to the Shifter

Post by russellnash »

Thanks for confirming that.
russellnash
Posts: 114
Joined: Fri Mar 26, 2021 2:46 pm

Re: No clock signal to the Shifter

Post by russellnash »

Anybody know what makes IPL2 always low? Thinking that might be significant. I have got the board so that all data lines D0 to D15 are oscillating but all the address lines are stuck high. One thing that is noticeable is that IPL2 stays low from the second that I switch on and also by reset. The pull up for IPL2, pin 4 on RP4 measures 4.7K. All pull ups pass the resistance test.
The CPU, GLUE and MMU are confirmed working and the PLCC socket contacts pass a continuity test that I did using a pin to actually touch the chip contacts rather than just the socket contacts.
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