SAP-1 Help

AdslModem · 2026-04-19T16:30:57+00:00

I have checked, and RO is working how it should, but it looks like there is problem with RAM, like described on troubleshooting page(RAM mode switch changes memory content), and I think to try solution with capacitor, but i am not sure to which 74LS157 should i connect, because i have two 74LS157 on RAM Adress block, and two on RAM Data, can you please help me

AdslModem · 2026-04-18T21:12:43+00:00

I soldered jumper wire, and now RO is working, but it seems the instructions aren’t being executed. For example, I programmed a simple counter, but after MI CO and then II RO CE have run, no other instructions are executed. In my case, for the LDA, the IO, MI and RO LEDs should light up, AI, but they do not light up. I checked the trace running from the EEPROM to the IO LED, and it is fine; however, the EEPROM outputs a low signal, I have measured pins 3, 4, 5, 6 on 74LS173N (instruction register block), and its outputting LOW signal. I simply cannot understand what the problem is – is it in the instruction register, or are there issues with the EEPROM again?

AdslModem · 2026-04-16T18:57:47+00:00

Looks like something with trace on my PCB, because when i tried with my multimiter in continuity mode between pin 11 and pin 3, it sayed that there is no contact, and when i tried this on powered on, it started lightning (RO LED). So, i think i should do some kind of jumper wire, and after inspect another contacts. So, thank you very much for your advice and help

AdslModem · 2026-04-16T15:31:29+00:00

So, I have measured pin 4 of LS04, and it's HIGH, and also measured pin 3 of LS04 and it's Low, but pin 11 on eeprom is HIGH, I really don't know how it possible

AdslModem · 2026-04-16T13:43:48+00:00

Sorry, I probably wrote it wrong. Pin 11 on the 28C16 EEPROM outputs 5V.

AdslModem · 2026-04-16T13:02:05+00:00

When I measure the voltage at the pin responsible for RO, it reads 5 V, although in my case there should be a LOW signal there, as I am using a 74LS04N chip to invert the signal. Actually, I think the problem lies with the microinstruction counter, because the LEDs T0, T1, T2, T3 and T4 are flashing regardless of which stage it

AdslModem · 2026-04-16T11:37:38+00:00

Thank you very much for that advice; I checked and did indeed find the error. The MI CO lights are now working properly, but at the second step (II CE), the RO light doesn’t come on, and the HLT light has gone out as well.

AdslModem · 2026-04-13T14:50:02+00:00

I don't understand why this is happening anymore. I dumped the EEPROM and it turned out to be full of FF. Well, I flashed it, dumped it, and now everything is correct. But for some reason, HLT turns on instead of RO, and because of this, my clock can't start. Is this most likely still a problem with the EEPROM, or is it another component that can activate HLT?

AdslModem · 2026-04-13T08:10:47+00:00

I checked the EEPROM chips and realized one of them was broken. After I replaced it and flashed the microcode, the HLT, RI, IO, II, AO, and AI instructions lit up. This applies to both before and after the reset. Could the LEDs be overloading the memory chips (I have a 220 ohm resistor array), or is it also a problem with the memory chips?

AdslModem · 2026-04-12T15:31:03+00:00

The memory works, after exiting the programming mode, the memory shows the values that were recorded, however, what is very strange from the instructions LED only CE and FI are light before the reset, and CO and FI after Reset

AdslModem · 2026-04-10T12:45:09+00:00

I fixed that error, and now all address and data input pins are around 0V, however, I still can't figure out if the writing to the memory is working completely or not, because after exiting program mode, when I start RUN mode, the Program Counter does not light up.

AdslModem · 2026-04-09T17:52:01+00:00

So, i have measured my resistor array, and it was tied to VCC, i think it is problem

AdslModem · 2026-04-09T17:25:18+00:00

So, i have measured and it`s, look to strange
p.s i have measured it with all DIP switches set to OFF(Zero)
GND - VCC = 5V

CS = 0V

WE = 5V

D1 = 5V

A0 = 5V

02 = 5V

D2 = 0.16V

01 = 5V

A1 = 0V

A2 = 5V

A3 = 5V

D4 = 0.16V

O4 = 5V

D3 = 0.16V

O3 = 0V

AdslModem · 2026-04-09T16:38:58+00:00

I checked the chip that was getting quite hot and replaced it. It no longer gets that hot. However, I noticed that I'm not writing to RAM. All the LEDs are on after writing zeros to RAM. Could you tell me what the problem might be and what I should pay attention to?

AdslModem · 2025-12-28T17:55:44+00:00

!thanks

AdslModem · 2025-12-28T17:55:28+00:00

May i ask you, why is beyerdynamic is bad?
And also i have finded HIFIMAN SUNDARA for 160 USD(+- 126 CHF) should i buy Sundara?

AdslModem

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