
DRAM Tester for ZX Spectrum, C64, Oric, Jupiter Ace and other retro computers and equipment.
This DRAM tester supports 1 bit DRAM devices from 4Kbit to 256K bit (eg. MCM4096, M4027P, 4116, TMS4532NL3/4, M3723L/H, 4164, 4128, 41256, etc.).
It has a simple power requirement, needing just 5V and drawing less than 100mA, so it can be powered from any USB port with a standard micro-USB cable. The tester generates all of the required voltages (+3V3, +12V, +5V and -5V) from this single supply.
How to Use
Please note that the LEDs will flicker while the DRAM is being tested, this is normal.
Example Results
LED Off |
No Block |
LED Red |
Bad Block |
LED Blue |
Good 4Kbit Block |
LED Green |
Good 16Kbit Block |
LED Magenta |
Good 64Kbit Block |
Test Times
The tester is pretty fast, based on a modern 32 bit ARM micro-controller running at 64MHz.
Here are some examples of the test times for this tester:
Type |
Size |
Approximate Test Time |
4027/4096 |
4Kb |
About 2 seconds |
4116 |
16Kb |
About 5 seconds |
4164 |
64Kb |
About 19 seconds |
4128 |
128Kb |
About 37 seconds |
41256 |
256Kb |
About 75 seconds |
The tests are made such that the refresh period is close to the specified maximum retention time for the part being tested.
That means close to 4ms for 64 rows on an M4027 or MCM4096, 2ms for 128 rows on a 4116 part and close to 4ms for the 256 rows on a 4164 or 41256 part.
This ensures that any issues that only occur near to the maximum retention time are also detected by this tester.
So you can be pretty sure that if a part tests as good in this tester then it should work well in a real application.
The Test Procedure
1. Measure the size of the DRAM.
2. High speed tests
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