Mark’s Repair Blog


Welcome to my tech blog page! A brief summary what you can read/see here:

All about my audio repair
I’m not a professional, although I’ve been busy fixing audio equipment for quite some time now. I don’t nearly know all about repairs, but since a lot of defects are related to it’s age, years of use, wear and tear a lot of fixes are the same in the basics.
As an amateur photographer I usually make a lot of images with my DSLR or smartphone to keep track of repairs and document the constructions after disassembly. These come in very handy to illustrate repairs in a blog.
Because a lot of interesting work has been done a long time ago, I will add those as well and change the date back to the time I was working on these repairs.
A nice timeline will then eventually start to show in the index on the right.

DAC and transport list CD players
My interest in the Philips TDA1541A D/A converter and the search for affordable and good second hand CD players asked for a good source of CD players and what type of DAC and transport/laser unit is used.
I’ve created my own list and uploaded it into a WordPress table. Now I can easily search for brand, model, DAC or transport type as I ran into an interesting sale.
The total list now counts a total of over 4000 CD players of all kinds of brands/models. If you have your own list or if know new brands/models, please let me know, then I’ll add those to the list.

Reverse engineering NSM4002 and NSM4202 LED displays
In the early days of the CD-Player (in the 80’s) several CD-players got a 4 digit 7-segment display unit with an integrated controller chip. After several years of use, those displays starting to break down. One or more segments will fail, sometimes they come back to live as soon as the CD-player is warming up.The fact is that it’s not the LED itself that is failing, but it’s the driver IC that is not working anymore at that output.
Unfortunately those old displays are not available anymore. There are a few locations (ebay etc) who sell replacement displays, but these are build using separate 7-segment displays, not the original 88:88 format 4-digit 7-segment display.
Another thing that bothers me is that those single 7-segment displays have a much more modern look with rounded segments than the original ones.
Because of that and the need for me to repair those CD-players and bring them back in the original state, is that I thought of creating one by myself since there is nothing similar available.
The development of this replacement display will soon be added to this blog.