Tektronix 2430A Startup Failure - Page 1
Forum section: electronics / repair

author: Jimmy Electron
author_rank: Contributor
timestamp: March 03, 2025, 09:39:51 pm
content: Looking for help diagnosing this 2430A dated April 1989 with serial #B040823.When turned on, all the GPIB led's light up as well as sequencing though the 'Trig'd, Ready, Arm, + and -- ' led's, before going 'BEEP' and stalling with an immovable, unchangeable dot to the right hand side of the screen. No readout, no trace. (See photo)The only led's remaining are the GPIB 'LOCK' and the '+' symbol. No vertical nor horizontal deflection and no effect from any control button or knob other than the odd BEEP if pressing the display buttons.Before anyone asks, I have no idea as to the history of this unit although it is pretty clean for it's age.Tests show that all the LV rails, as well as the 1.9kV HV are present. The CRT heater has continuity and 6v supplying it (although it doesn't glow as I would have expected). I've reseated all the socketed IC's, Hybrids and connectors and probed the vast majority of caps, diodes and transistors for shorts. Only the main board remains for that.Looking through the manual in the 'Display Troubleshooting' section, I've come across two sticking points. One being that ZINT on pin 2 of U227 on the HV board doesn't vary when DISPLAY INTENSITY is adjusted however the manual only offers the FORCE DAC test as the next step and obviously without a display then that isn't possible.Secondly, in the DAC SYSTEM FAILURE section it states that, 'if TP650 and TP660 are good then the DAC system is operating normally to this point' and to 'troubleshoot the DAX Multiplexer (u831, U821, U830) and the indvidual DAC output ports'.These test points ARE good, but it doesn't say HOW to perform this troubleshootingAs for the BEEP, the only reference I found states that when there is a short in the unregulated voltage section then the scope 'Chirps' and reboots continuously. This unit doesn't reboot.Anyone have any ideas?Is there a way the DAC10 IC's can be tested manually? They don't run instantly hot. Pins 2 and 4 are the I/O's however I'm not detecting anything. The supply voltage reads at 29v.Manual can be found here....https://www.tek.com/en/manual/2430a-service-manualMany thanks in advance

author: Kwakerman
author_rank: Regular Contributor
timestamp: March 03, 2025, 10:46:19 pm
content: Can't really help with this but you don't need to be concerned about the heaters as it is obviously working as you have a spot on the screen. Might be worth looking at the alignment procedure as that should tell you where to measure the DAC voltage and what the range should be, if it is wildly out of limits then worth having a look around there but I'd be more focussed on the digital microprocessor area if it has locked up on start.

author: Jimmy Electron
author_rank: Contributor
timestamp: March 04, 2025, 12:43:50 am
content: Thanks for the input. Nice one!I've spent the last two full days going over the manual, then the scope, then the manual etc. following all the instructions in the section 6, and I've now taken it off the bench as I no longer know what or how to further test. The manual gets to a point then says to, 'run auto tests or Force Dac' which require the display.Seems that without a working display then it is next to impossible to identify where the problem lies?Maybe it 'is' in the microprocessor area?Maybe it's on the side board?Maybe it's on the main board?Perhaps it's the HV section?Maybe it's in the front panel?Maybe it's in the DAC's?Maybe it's in the Hybrids?Maybe it's an IC or transistor?Maybe it's a shorted capacitor?Maybe it's a shorted diode?The only section I'm certain that it's not is the Low Voltage power supply board.If I knew what the beep signified then it would help knowing where to look...

author: Kwakerman
author_rank: Regular Contributor
timestamp: March 04, 2025, 09:03:46 am
content: I assume you don't have access to another (working) scope to check data lines / clocks etc? If you don't then I think you will struggle with this type of fault if you just have a DMM.

author: BradC
author_rank: Super Contributor
timestamp: March 04, 2025, 12:04:27 pm
content: Quote from: Jimmy Electron on March 03, 2025, 09:39:51 pmPotentially silly question, but is it just sequencing the lights or is it flashing out an error code as detailed on pages 6-27 to 6-29 of the service manual?

author: Jimmy Electron
author_rank: Contributor
timestamp: March 04, 2025, 11:11:05 pm
content: That's probably not such a silly question.been out all day but shall run the scope and see if it is speaking Tek cypher code or not, but thanks for that heads up as I had no idea it existedSo... The 'code'...TRIG'D (2 secs)READY (one second)All LED's flashing (3 times)TRIG'D (one second)All LED's flashing (1 time)TRIG'D, READY, PLUS SYMBOL (4 seconds)Then the following in quick succession...ARM,TRIG'D,READY,PLUS SYMBOLAnd it stalls on the PLUS SYMBOL with the dot on the displayIs that code or just insane ramblings?I'm reading the manual but it may as well be in Chinese. I mean wtf does 'delimitthe first digit of the code' mean?Attaching the code below for any sleuths who fancy a go...

author: Jeff eelcr
author_rank: Frequent Contributor
timestamp: March 06, 2025, 12:05:47 am
content: I just had a 2430A with no display it turned out to be a 2.7UF tant cap (top PCB rear left) that was loading a reg circuit.I am waiting on a replacement but removing it brought back the display.Jeff

author: Jimmy Electron
author_rank: Contributor
timestamp: March 06, 2025, 12:34:39 am
content: Hi Jeff.thanks for the input. Do you know the 2.7µF cap number?Was your scope flashing the LED's as it was attempting to start?

author: BradC
author_rank: Super Contributor
timestamp: March 06, 2025, 04:35:53 am
content: Quote from: Jimmy Electron on March 04, 2025, 11:11:05 pmAt first glance that looks like an error code. In a normal boot you should not get *all* of the trigger lights on at the same time, as that is the *delimiter* between code digits. Having all lights flash 3 times though does look a bit like an 000 so it may be 0001 and I can't find that in the manual. Any chance of a video? I'm flat out working and frankly my brain is too fried to try and interpret it at the moment.What I can do is show you what my 2440 looks like with a normal boot :https://www.fnarfbargle.com/private/250306-2440_Boot/IMG_3122.MOV

author: Jeff eelcr
author_rank: Frequent Contributor
timestamp: March 07, 2025, 01:04:00 am
content: C181 2.7Uf 20V replaced with 173D275X9025V 2.7Uf 25V Mouser has in stock.It did start, yes LED's flashed but you could not tell as there was no display.Jeff

author: Perrold
author_rank: Contributor
timestamp: March 08, 2025, 10:18:07 am
content: Probably a long shot, I had a 2445B years ago that would not do much. A few front panel LEDs would light up and there no response from the front panel controls. I want to say there was no beam visible unless the beam find button was depressed and then it was just a dot. Ultimately the root cause was a bad 10k resistor in the Vref circuit for the DAC. Might be worth poking around there though the way your Vref is implemented is different. All other troubleshooting up until that point was of no help as so many system functions rely on the DAC being functional.

author: Jimmy Electron
author_rank: Contributor
timestamp: March 08, 2025, 07:25:45 pm
content: Hi mate.Not sure where to upload a video to?

author: BradC
author_rank: Super Contributor
timestamp: March 09, 2025, 02:11:04 pm
content: Quote from: Jimmy Electron on March 08, 2025, 07:25:45 pmSent you a PM.

author: BradC
author_rank: Super Contributor
timestamp: March 10, 2025, 12:10:44 am
content: G'day Jimmy Electron,Your video is here :https://www.fnarfbargle.com/private/250310-2430-Startup/P1050776.MP4If I've interpreted it correctly, that error code looks like 2221 to me. Codes 2221-2224 are the Mode Control register (MODECON) according to the manual.