Neutrik TP401 / MJS401D Service Manual - Page 1
Forum section: electronics / testgear

author: Nevada
author_rank: Contributor
timestamp: January 01, 2024, 06:25:51 pm
content: Does anybody have a service (or any) manual for the first generation neutrik Audio Tester?

author: Richard_S
author_rank: Contributor
timestamp: April 20, 2024, 12:51:09 pm
content: Yes, I have an operation manual for the MJS401D. It is too big to attach here. The scan I have done is around 40MByte.

author: 707dave
author_rank: Newbie
timestamp: April 25, 2024, 09:18:07 pm
content: I too would be interested in a copy of the manual, I’ve a TP 401 and information is amazingly difficult to find for these units.

author: Richard_S
author_rank: Contributor
timestamp: May 01, 2024, 07:06:26 pm
content: Hi. Happy to share a scanned copy of the user manual on DropBox. Just shared with another Dave recently.

author: 707dave
author_rank: Newbie
timestamp: May 03, 2024, 09:25:52 am
content: Oh yes please - that would be perfect. Thanks D

author: AlexMUK
author_rank: Newbie
timestamp: June 05, 2025, 04:14:43 pm
content: Hello,I've been searching high and low for a copy of the user operation manual. I'd be most grateful for a CES to your scanned PDF!.Thanks in advance,Alex

author: AlexMUK
author_rank: Newbie
timestamp: July 01, 2025, 07:08:11 pm
content: Bump... Sorry for the dead thread resurrection.I'd still very,very much like a copy of the manual if anyone has access.. there are literally two threads I. The I ternet discussing this, and this is one!

author: stevezodiac
author_rank: Newbie
timestamp: August 25, 2025, 02:28:25 pm
content: Hi there, could anyone share the link to the scanned PDF for the MJS401D please?I have one of these with a fault that I am trying to fix. On power on the meter moves and goes back to the central position but the digital display is blank and none of the keys work - although some of the red LEDS are lit. However if it is set into Diagnostic mode - by holding in the Level Key in when powering On - then the word "Diagnostic" is displayed and some of the first 5 keys allow some modes to be selected. So it appears much of it is working, but not the key scanning or display when not in diagnostic mode.Any available advice or documentation would be very much appreciated. Thanks

author: AlexMUK
author_rank: Newbie
timestamp: September 25, 2025, 03:26:15 pm
content: Hi Steve,Nothing to offer from me, but I'd also like a copy of the service manual and/or user manual. I have a MJS401D that may be in need of calibration, but otherwise seems to work ok. Do you have access to the user manual? if so, could you share?.I've tried contacting Neutrik T&M in the UK, but didn't get a reply to my request. There are still a few web links to people providing calibration services for the MJS401D, so they may be able to help with the documentation.From your description, it sounds as though the CPU board is working ok. Check the ribbon cable between the CPU board and front panel - if you're getting into diag mode, then at least some of the key scanning is working ok?.Please do share any documents you find, and I'll do the same!.Regards,Alex

author: stevezodiac
author_rank: Newbie
timestamp: September 29, 2025, 04:05:25 pm
content: Hi. By a process of elimination I have found that if it is powered on with the complete MD404B Oscillator module removed, the display lights up and the keys work and they select functions - its not perfect but it does appear to work apart from the oscillator.From scouring the internet this appears to be an optional accessory unit. Its a complex beast.https://www.worldradiohistory.com/Archive-All-Audio/Archive-Studio-Sound/80s/Studio-Sound-1984-11.pdf- page 81 shows the unit without the oscillator module fitted - between the meter and power on/off switch at the right hand side. This link in the new products section shows it WITH the optional Osc unit.https://www.worldradiohistory.com/Archive-All-BC/Archive-All-Audio/Archive-DB-Magazine/80s/DB-1985-03-04.pdf- Copy and paste the links if necessary.This is a triple layer module crammed with IC's. I removed the top 2 layer boards (presumably the oscillator sections) and tested with only the base layer connected (module reinstalled) - still no display or functions. With it removed - display and buttons work.So possibly the base layer pcb is the cause. It also has a 6502 processor on board.The base layer is also home to 3 regulator ICs and 3 power transistors plus 5 large wattage carbon resistors. One of them is tucked up next to the heatsink of a small power transistor and its banding is discoloured so its difficult to know what its true value is. The remaining 4 are obvious from their colour codes and they measure as they should. As the fault report was that it was left powered on overnight and had decided to be faulty the next day it does 'smell' of a power supply fault. This board looks like it has its own on board power supply regulation. Maybe when it loses power it ties up the data lines for the rest of the system.Because this unit is buried inside a metal cage, live fault finding is impossible without an extender board. It would be easier to find dinosaurs than one of those.If there was a schematic or at least a parts list for the MD404 module it would be helpful... until then I shall keep investigating.