API 525 card connector pinout mod
Old 5th November 2003
Lives for gear

Thread Starter
API 525 card connector pinout mod

I would like to modify 4 vintage 525 modules I have to work in current API frames. I know the old modules' card edge connectors have a different connecter pinout than current ones and have to be modified. I contacted API who will do it for $110/hr at an estimated 2 hours for each unit. I am technically competent to do such a mod. I just want it to be by the letter so that the units are not operationally affected and that they retain their value. Does anyone have any experience with this? How does API do it? Their tech mentioned cutting traces, drilling holes and running wires to new locations. Do they just cut the traces to the appropriate edge connector then drill a hole and solder in a jumper to the correct location. What about length and type of jumper wire, etc? For reference on these units 3 have the "Studio Systems division of Automated Process, Inc" out of Farmingdale NY badge. 1 has a "Automated Process, Inc" badge out of Melville, NY. They came out of an old custom post production board that had API and ADM modules. I have a mind to just send them to API so they can be fixed and blessed as factory refurbished but I know it's a fairly easy mod. Any info or reference help appreciated.

Old 6th November 2003
Gear nut
bradavenson's Avatar

Odd this should come up. I just did this mod a few days ago. It is quite simple and with some care I'm sure yours will turn out as good as the API guys can do it. I just looked at the two pinouts and made the appropriate changes so that the module matched up the new pinout. It took me about an hour to do one module.
Old 14th March 2012
Gear interested
Also looking for info on the mod

My boss is looking into getting 2 vintage API 525's. I have read that you have to cut off 2 pins, cut some traces and make some jumpers to get them to work in a lunchbox. They are not modded and I am more than competent to do the mod myself i just cannot find any documentation on the subject. Can anyone point me in the right direction?
Old 16th March 2012
Gear nut
bradavenson's Avatar

Old 16th March 2012
Gear interested
Yeah I was just emailed the same thing by the API Service department. Those guys are really helpful! My boss is going to have a local guy do I who has done the mod before.... After looking at it I could totally do the mod myself but I guess he doesn't want me working on gear that's over 15 years older than I am haha.
Old 5th December 2012
Gear nut
LoFiAudio's Avatar

API 525 (vintage) Pinout Mod - w/ Pictures

So I looked around here for some detailed information regarding the pinout of vintage API 525 compressors, and how to modify them to get them to work properly in modern API / other 500 series racks. There's one page out of API's service manual that was linked above (copied here as well) that shows the proper pinouts for both the 550 eqs and the 525 compressors, and how to change them. Aside from that there seems to be nothing out there on how to do this, so I'm going to post some pics of the mod in case future gear / geek slutz need the info. The mod was pretty easy for me, but I am somewhat experienced with a soldering iron. I'd say the hardest part was trying to bring myself to start molesting and changing the circuit on these beautiful vintage compressors that I just spent a lot of money on!

Here goes. Of course modifying your own vintage gear comes at your own risk. I'm just a moron on the internet, so please do your homework and don't take my word for anything!! Also my circuit boards are Revision F, so if you have a different revision, your circuit may be different! Check and refer to the sheet from API if in doubt!

1. Remove the Yellow / Brown Wire that connects to pin 3 at the edge connector. This is the only thing actually connected to pin 3. Also remove the Blue and Yellow wires from pin 10 & 11. These were for the VU lamps, and used to work on +24vdc but they will run on +16vdc and we will hook them back up at the end of this process.

2. Cut traces going to Pins 4 thru 9. Cut them as high up as you can, you don't want to be soldering directly to the pins as the module may not seat properly if you get too much solder on a pin. IN Circuit revision F, you do not have to cut the trace from pin 3 or the pins 10 & 11, as we just disconnected them above. If your circuit is NOT revision F, please refer to API's documentation to make sure this is still the case!!

4. Drill holes. I used a long pointy drill / awl attachment for the Dremel, and it worked great, although I'm sure a tiny drill bit would work fine. Don't make the holes too big, as you want to be able to reverse this if anyting doesn't work! You need to drill holes in the card side (on the inside of the split traces) for pins 4, 5, and 6, and 12 (12 is for the lamps, optional). You'll then need to drill holes on the pin side of the split for pins 4, 5, and 8. You may have to expand the hole in pin 10 as well to get your jumper to fit.

5. Next, take the yellow / brown wire coming off of the transformer that was attached to pin 3. Again, this is revision F, so the color wire may be different on your unit, just make sure you're getting the wire that was attached to pin 3. Solder it into the hole in the pin 4 connector pin, being careful not to get too much solder on the pin.

6. Put the first two jumpers in place - from pin 4 (on the card side of the spilt traces) to pin 5 takes about 1/3", from pin 6 (card side) to pin 8 takes about 1/2"... Then put the last jumper in place, from pin 5 (card side) to pin 10, which is about 1" in length. Solder them in very carefully!

7. Next you'll want to make the lamp work, even though it's just going to be 16vdc, and they aren't extremely bright. This step is optional, and it does not affect the compressor's operation. To do this you will insert the blue wire that came from pin 10 into the small hole you drilled near the top of pin 12. Then take the yellow wire you took out of pin 11, and insert it into the already present hole in the trace coming from pin 13.

Next, test them out and see what happens, you should be good to go at this point!! Below are some pictures of the process, hope it is of help to someone in the future.

API's Instructions in a nutshell:
OLD Pinout ---> NEW Pinout (cut traces on pins 3-11)
3 ---> 4
4 ---> 5
6 ---> 8
5 ---> 10
Attached Thumbnails
API 525 card connector pinout mod-api-525-guts-top.jpg   API 525 card connector pinout mod-api-525-guts-btm.jpg   API 525 card connector pinout mod-original-pinout.jpg   API 525 card connector pinout mod-cut-traces-4-thru-9.jpg   API 525 card connector pinout mod-drill-holes-.jpg  

API 525 card connector pinout mod-holes-drilled.jpg   API 525 card connector pinout mod-1st-two-jumpers-.jpg   API 525 card connector pinout mod-finished-product-.jpg  
Attached Files
File Type: pdf API 525 edgeconnectorpinswap.pdf (434.8 KB, 145 views)
Old 4th January 2014
Lives for gear
Seditionary's Avatar

Thank you for this!

Now my 525 is working for 500 series!

As the board in my 525 is a bit different... I didn't do the lamp modification... the one thing that doesn't work is the meter... would the lamp mod have anything to do with getting the meter to function? If not, any suggestions? Maybe I just have a bad meter? It is the large vu meter 525.

Anyways, my 525 is up and running in 500 series and sounds great... just would be cool to get the meter working too

Thank you.
Old 2 Weeks Ago
Lives for gear
Seditionary's Avatar


I'm bumping the thread again with photos

I would really love to get the meter working!

Here are some close ups of the work I did, moving gradually further out so that you can see the revision board I am working with. Again -- the modification made the 525 work great in the 500 series rack! However, the meter isn't working... probably because I didn't complete that final step in the mod. Please help api electronic gurus! Thanks many times.

Old 1 Week Ago
Lives for gear
Seditionary's Avatar

Originally Posted by LoFiAudio View Post
So I looked around here for some detailed information regarding the pinout of vintage API 525 compressors, and how to modify them to get them to work properly in modern API / other 500 series racks.
Any idea why a meter might not work?

Thank you dear friend.
Old 1 Week Ago
Lives for gear
Seditionary's Avatar

Originally Posted by bradavenson View Post
It is quite simple and with some care I'm sure yours will turn out as good as the API guys can do it.
hey brad! do you have any suggestions for why a meter would not work? do you think the meter might just be dead independent of the mod?

thank you, thank you.

i posted photos above
Old 1 Week Ago
Lives for gear
Seditionary's Avatar


Anyone have any suggestions on this?

Thank you again in advance!
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