Atari 520STe Problems - Help Please

[1024MAK]

Should pins 6,10,15 be pulsing?

Yes, the "master" clock input is pin 15 which is a 8MHz clock. By clock, I mean a square wave signal.
If this is missing, the MPU will do nothing.
Pin 6 (AS) is pulsed by the MPU every time it puts a valid address on the address bus to talk to ROM, RAM or any of the other chips.
Pin 10 (/DTACK) is an input to the MPU that tells it that the device it is talking to is present.

Depending on what type or model of logic probe you have, if there is a high frequency digital signal present, it should show both a high and a low indication at the same time, or show a pulsing indication.

Do you have access to a good oscilloscope? By this I mean a 50MHz type or better.
Logic Probes are not normally much use when investigating 16MHz and 32MHz clock signals.

But one thing you can do, check U405 (74S257) pin 1 with a meter and/or a logic probe to confirm that you have a high (+5V) level here.

Mark

[LoGiCa]

My logic probe has a pulse indicator led.

None of those pins on the 68000 are showing a pulse, just low or high.

I tested the u405 and it reads 5v on pin 1

I don't have access to an oscilloscope here.

[1024MAK]

Well anyway, the path of the various clock signals is given below.
It starts with a 32MHz clock generator (oscillator). Then various chips process, switch or divide the clock. Each time the clock is divided, the frequency is halved.

So working backwards...

The 8MHz MPU clock ("CLK8") comes from U400 (STMCU, the memory controller).
This gets its input clock (pin 2, I think) from U401 (GSTSHFTA, the video "shifter") pin 52 and should be a 16MHz signal.
The clock input for U401 (GSTSHFTA) is pin 53 (here the clock is called "MC")

U405 (74S257) pin 3 is the 32MHz input clock and pin 4 is the 32MHz output clock.

The source of the 32MHz clock depends on the PCB version that you have?
Do you have a UK version with a modulator (you have a UHF aerial connector)?

Also do you have another STE that you can swap chips between?

Mark

[LoGiCa]

Thanks for your time on this I appreciate it

I won a 1040STe on ebay just now so I will have another board to test chips etc.

The STe I have is a UK with TV modulator.

[goolash]

So working backwards...

The 8MHz MPU clock ("CLK8") comes from U400 (STMCU, the memory controller).
This gets its input clock (pin 2, I think) from U401 (GSTSHFTA, the video "shifter") pin 52 and should be a 16MHz signal.
The clock input for U401 (GSTSHFTA) is pin 53 (here the clock is called "MC")

U405 (74S257) pin 3 is the 32MHz input clock and pin 4 is the 32MHz output clock.

Thankyou, your post saved one dead STE unit. I bought 520 STE in non working condition. It had faulty PSU, CPU and dead both ROMS. Although I changed everything there was no single sign of life. No output on monitor (black screen), nothing came on diagcart. I have no osciloscope for checking the 8Mhz. Long story short it was dead U405 (74S257) that caused the issue and this post helped me a lot.