Electronics > Repair

Looking for Mettler Scale ROM backup

<< < (7/11) > >>

gmac34:
Did you check continuity between the uvprom and the board? Check that all data line are going trough the connector, also check for corrosion or bent pins.

dustooff:

--- Quote from: jamarjan on October 18, 2024, 10:26:08 am ---In most cases I have no activity on pins of channel 1 (P1.X) where communication with ROM should be.

--- End quote ---

Is port 1 actually connected to the ROM/RAM devices?
My understanding of the data sheet says...
Port 0 is also the multiplexed low-order address and data bus during accesses to external program and
data memory.
and
Port 2 emits the high-order address byte during fetches from external program memory and during
accesses to external data memory that use 16-bit addresses.

In the past I have repaired two PM4600's one for VFD problems, the other was failing to startup, like your current situation, unfortunately I can't recall the specifics of how the repair went. And I currently own it.

Edit: found app note AN457 (but not on NXP's site)  look at Figure 20, the 74HC373 has to hold the low address while the MCU presents the data byte.
Check the 373 output for an address, may need a LA to do that.

jamarjan:
I've had a brief break in fixing the scale due to a business trip.
I replaced the UPD446C CMOS SRAM, 74HC373 chip, uC P8031, and the resistor ladder (it looked like it had a crack).
Still no change.
The clock waveform is still not square.
On startup there seems to be some activity on the uC communication with the ROM.
However, it seems to me that it does not load the program.
I guess I actually need to equip myself with a logic analyzer and take a look at the uC - ROM communication.

gmac34:
Sorry to hear that the part’s cannon approach didn’t lead to anything.
In a few days I will be back home, if you need I can probe around on mine and compare things.

jamarjan:
I managed to play around with a logic analyzer
I am posting screens from channel P0, P1 and from the EPROM
it seems to me that the microcontroller is not reading data from the eprom
just why it is not displaying any error on the VFD
gmac34 - can you check how your scale behaves when you unplug the connector ( blue) from the weighing module? and how about when you unplug the interconnect board with the rear connectors?

Navigation

[0] Message Index

[#] Next page

[*] Previous page

There was an error while thanking
Thanking...
Go to full version
Powered by SMFPacks Advanced Attachments Uploader Mod