Products > Test Equipment
Data Precision 2020 Function Generator repair
ioprev:
--- Quote from: srb1954 on April 11, 2020, 10:59:29 am ---I also have a Data Precision 2020 for repair. It has a bad PSU and I haven't made much progress on it yet.
The PSU in mine (Todd MAX354-9920) differs from yours but it has a separate header with a connector pin labelled PF, which is presumably stands for Power Fail.This would allow the CPU to shut down in an orderly fashion if there is a power failure. A wire connects from this pin to pin 5 on the power connector on main backplane. Presumably this is a logic level signal, which would explain the 3.8V you are reading. It might pay to check to see if this signal changes state as the unit is powered on and off.
I can't verify the state of this signal on my unit due to the PSU not working properly.
Good luck with your repair efforts. If you manage to find any schematics for this unit please share them with the community. This device is a very interesting piece of test gear but there seems to be practically no documentation available for it.
--- End quote ---
In case you haven't seen that already, I found some info for your supply here: https://store.dbgweb.net/max-354-9920
Pin 5 is indeed the power failure pin, but seems to be active LOW from what I’ve seen on mine.
Meanwhile, I measure 24 Ohm resistance on mine, between 5V and GND which I don’t think is a good sign...
Im going to tear down the main board assembly tomorrow, desolder all caps and check if there is a short somewhere. There are around 15 tantalums on main board which need my first attention.
Apart from the tantalums, near every single logic chip, there is an A5E104M, which by the name I suppose are 0.1uF caps. They look like a rectangle version of a ceramic cap.. Are these also failing that often?
Rerouter:
Ceramic caps are fairly safe, I have not yet seen one in a decoupling role fail, there voltage rating is usually the highest on the PCB, value shift yes, fail partially shorted no.
srb1954:
From your sketches the circuit appears to be a simple level detector on in the incoming supply to the regulator so it forms a crude early warning power fail indicator.
Looking back at the picture of the main CPU board the red arrow points to pin 32 on the MC68230, PC2/TIN. This pin can function as either a general purpose I/O line or a timer clock input. It could be that the S/W configures this input as a timer control to generate an interrupt signal out of the MC68230 with activity on the PF line, possibly after a short time delay.
Check to see if there is any activity on the PC3/TOUT line (MC68230 pin 33), which can be configured as an IRQ output from the timer subsystem. If this IRQ line is stuck low then the main processor is being continuously interrupted and won't be able to run normally.
ioprev:
--- Quote from: srb1954 on April 12, 2020, 12:49:26 am ---From your sketches the circuit appears to be a simple level detector on in the incoming supply to the regulator so it forms a crude early warning power fail indicator.
Looking back at the picture of the main CPU board the red arrow points to pin 32 on the MC68230, PC2/TIN. This pin can function as either a general purpose I/O line or a timer clock input. It could be that the S/W configures this input as a timer control to generate an interrupt signal out of the MC68230 with activity on the PF line, possibly after a short time delay.
Check to see if there is any activity on the PC3/TOUT line (MC68230 pin 33), which can be configured as an IRQ output from the timer subsystem. If this IRQ line is stuck low then the main processor is being continuously interrupted and won't be able to run normally.
--- End quote ---
Thank you a thousand times for this!!! This evening I had somehow convinced myself that pin 32 was ~CS...
Now it makes much more sense!
ioprev:
--- Quote from: Rerouter on April 11, 2020, 10:19:09 pm ---Ceramic caps are fairly safe, I have not yet seen one in a decoupling role fail, there voltage rating is usually the highest on the PCB, value shift yes, fail partially shorted no.
--- End quote ---
Indeed, they are ceramic caps from AVX.. Never seen this package before :)
Voltage rating is 50V (!)
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