Sold 4164/41256 DRAM (memory) chips tester for C64 and more

Status
Not open for further replies.
Hi anemo,
I've been looking at the schematics that this device is based on and there's a major flaw in the design. There are neither current limiting resistors nor buffers between the µP and the DUT. This means that if any one of the RAM's pins is shorted to ground (which is extremely common on failed RAMs) the current will instantly exceed the allowed 40mA per pin of the µP and the Arduino is permanently damaged. So the device will only work until it has actually tested a bad chip?!

Bryce.
 
Last edited:
Hi anemo,
I've been looking at the schematics that this device is based on and there's a major flaw in the design. There are neither current limiting resistors nor buffers between the µP and the DUT. This means that if any one of the RAM's pins is shorted to ground (which is extremely common on failed RAMs) the current will instantly exceed the allowed 40mA per pin of the µP and the Arduino is permanently damaged. So the device will only work until it has actually tested a bad chip?!

Bryce.

My version has a polymer PTC fuse to cut off the DRAM if the current draw is too high. But sure, there could be additional protection per pin.
 
The PTC only protects the supply voltage to the DUT. Many 4164's that I've removed from countless machines had either an address or data line shorted to ground. These would detroy the tester (the Arduino, not the tester board itself).

Bryce.
 
The PTC only protects the supply voltage to the DUT. Many 4164's that I've removed from countless machines had either an address or data line shorted to ground. These would detroy the tester (the Arduino, not the tester board itself).

Bryce.

Thank you for your input! I'm looking forward to see your version.
 
I've started working on it, which is why I spotted the issue. Unfortunately this also makes the device a lot more complicated.

Bryce.
 
New batch and upgraded version (v1.2) now available!

New version has Arduino Nano output pins overcurrent protection (if DRAM chip is short circuited).

Slight price increase due to higher component cost and longer time to assemble.

Was €25.5 (v1.0), now €27.5 incl. shipping.

First 5 available boards are reserved for the following guys (in this order) who previously has stated interest in this thread:
* mrr19121970
* botialoach
* SaviorX
* DonChaos
* Knecht

PM sent to each member!
 
Last edited:
New batch and upgraded version (v1.2) now available!

New version has Arduino Nano output pins overcurrent protection (if DRAM chip is short circuited).

Slight price increase due to higher component cost and longer time to assemble.

Was €25.5 (v1.0), now €27.5 incl. shipping.

First 5 available boards are reserved for the following guys (in this order) who previously has stated interest in this thread:
* mrr19121970
* botialoach
* SaviorX
* DonChaos
* Knecht

PM sent to each member!

Cool, great improvement. How have you implemented the current protection? Series resistors on each pin or have you done something fancy?
Do you have pictures of the new device?

Bryce.
 
New batch and upgraded version (v1.2) now available!

New version has Arduino Nano output pins overcurrent protection (if DRAM chip is short circuited).

Slight price increase due to higher component cost and longer time to assemble.

Was €25.5 (v1.0), now €27.5 incl. shipping.

First 5 available boards are reserved for the following guys (in this order) who previously has stated interest in this thread:
* mrr19121970
* botialoach
* SaviorX
* DonChaos
* Knecht

PM sent to each member!

Cool, great improvement. How have you implemented the current protection? Series resistors on each pin or have you done something fancy?
Do you have pictures of the new device?

Bryce.

Hi,

Yes, series resistors (three resistor networks, one hidden under the Nano) for limiting the current to <30mA per pin. Thanks for the heads up, BTW!

Check out the first post for updated picture.
 
No problem and top marks for making the revision (it will save you a lot of hassle too if people started sending them back broken).

Bryce.
 
Status
Not open for further replies.
Back
Top Bottom