Category Archives: R&D

LM338K

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As the adjustable 5A regulator LM338K is usually sold for around 100 currency units, anything well below this figure will very likely be a counterfeit part. I got some with a troubleshooting job and could not resist to check them.

While the printing already looks fishy, it seems to be what it claims to be, it behaves like any LM317/350/338 type regulator under low load. But when increasing the load, it quickly became clear that it is not a 338 as the current remained well below 2A and then suddenly dropped to zero.

So I opened up another specimen and had a quick look through a microscope – the die clearly says 317 (no photo made, sorry). But it does not even fullfil LM317K specs, here is the opened device running at around 0.9A

MM5824 replacement

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There are various approaches for replacing the MM5824 divider chip, prominently used in KORG PS3x00 series synthesizers.

Most are based on the replacement circuit KORG themselves used on their boards. It consisted of a Hitachi HD14520 and some passive components. Many replacements just use a competitor’s 4520 type counter IC and maybe adjust the values of the passive components.

What I encountered when using such replacements: when holding certain notes, the tone eventually became interrupted at random intervalls. The counters occasionally counted mutiplie times during one cycle of the input signal due to violation of the input slope. The original HD14520 allows for 15µs rise and fall time for all supply voltages between 5 and 15 volts, while for example TI allows 15µs at 5V but only 5µs at 10 or 15V VDD, and Nexperia calls for 3.75µs@5V, 5µs@10V and 9µs@15V.

The obvious solution to get rid of any manufacturer constraints was to add a Schmitt Trigger to the circuit, which I did for both clock inputs while keeping attention to the clock edge on which the original counter propagates.

RPL71 – Replacement for DAC71 series D/A converters

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As stocks of working DAC71 series converters are depleted I designed a plug-in replacement for both the current (I suffix) and voltage (V suffix) types, including both CSB and COB coding. While the code is selected by a solder jumper, the voltage type replacement needs an additional SO8 OP Amp, like an OP07, fitted. The “TRIM” pin is not connected, instead of this a 20-turns potentiometer is added to the RPL71 board allowing fine adjustment of the on-board 10,00V reference. Where needed, a buffered output of the reference can be provided by adding another OP Amp and a few resistors.

rpl71_1

Shown above is a DAC71-CSB-I replacement board (no I-to-V OP Amp on the upper right side) and without a reference outputs (missing parts on the lower corner) which is equipped with a 14- instead of a 16-bit DAC to save 10€ as this board is tailored for use in Sequential Circuits Prophet-5 synthesizers where the lower 2 bits are not used anyway. The actual use case is shown below.

rpl71_2

 

Data I/O 29B Programmer – Welcome in the 21st Century

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For my work on vintage electronics, I sometimes need a device programmer for (E)PROMs and PLDs my Labtool 48 cannot handle.
2708 EPROMs are one example, they need three supply voltages, 2532 EPROMs are another problem because of different pinouts between manufacturers and so on.

Therefore I bought a Data I/O 29B with an Unipak 2B adaptor some years ago on eBay – some more info and a photo here: http://en.wikipedia.org/wiki/Data_I/O)

The PC software for computer control mode was obviously not written with evolution in sense. I tried it on a Pentium III at 400MHz first, then on a Pentium MMX, but I got lots of transmission errors and timeouts although neither the COM ports of the PCs used nor the system 29B interface was bad.

Now I finally started the project to write a new, portable, GUI-based application to talk with the 29B.
The functions planned so far:

  • connect to programmer, request capabilities and report errors
  • select device from a list of supported devices, send family code to 29B and adjust memory buffer size
  • read from device to memory buffer and show checksums
  • write memory buffer to device
  • save memory buffer to disk
  • load file into memory buffer
  • verify device against memory buffer

Basic functions are already implemented, a 2708 is the only selectable device at the moment, which can be read and saved to disk. I use the default format MOS Hex (81) for data transfers from and to the 29B, which contains checksums for every record of 16 bytes which are compared with the actual data to make sure no transmission errors have occured. I have not yet checked what needs to be done to allow larger devices (>64k) to be handled with this format as it uses fixed 16 bit addresses, nor how 16 bit devices or even PLDs can be used.

The program is written in C++, using the Qt Creator as IDE and obviously Qt for GUI “artwork” and OS abstraction of serial and file I/O.
Here’s a very first impression, more to follow:

 

The hex editor on the right shows a file actually written with my program. The contents are from one of the Sequencer EPROMs of a SCI Prophet 10, by the way. Om mani padme hum!

Posted in R&D

Beware of the fake: CA3080E

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Today I was fouled by a parts seller.

The chips pretending to be CA3080E’s made by Intersil will never work as intended because they are fakes.
It’s a sad but common fact that expensive and/or obsolete parts are often counterfeited – either by cloning them (mostly with poor characteristics), re-labelling overstocks or rejects of a completely other chip, or simply selling empty packages. These “3080’s” are of the second kind, there is a die inside and some pn junctions can be measured on the pins. But all of them violate the necessary condition of having a diode junction between pins 5 and 4 (see pg.3 in the data sheet at http://www.intersil.com/data/fn/fn475.pdf ). Another important hint is the date code, which makes these chips rather bad fakes: 15th week 2007 – the competitor National Semiconductor has obsoleted this chip in 1998, so I’d guess that Intersil hasn’t made 3080’s in 2007 anymore.

Update 06-01-2011: The die inside the fake CA3080’s has a name, and its name is LM4250. I’m not sure whether these are good LM4250’s or probably rejects. Either way they won’t substitute for CA3080’s.

Update 07-01-2011: Today I measured a batch of 15 identically looking “3080’s”. I checked for the mentioned diode junction and found it for 2 out of this 15 ICs.
I’ve opened one of them and guess what: there’s a 3080 marking on the die! But as it is mounted in the same cheap-looking package as the LM4250 dies I have serious doubt that these two are real CA3080’s of the expected quality. Here’s an image of the die:

For those who want to read more about counterfeits: http://sound.westhost.com/counterfeit.htm