Pragmatic (now Tegam) 2711A Waveform Generator - Page 1
Forum section: electronics / repair

author: Old Don
author_rank: Regular Contributor
timestamp: October 04, 2017, 01:23:42 am
content: I picked up a "defective - sold as parts" Pragmatic 2711A waveform generator on fleabay. LCD display was all messed up with the LCD 5x7 dots all turned on for all 2 row x 20 characters. Reported that the waveforms not working or not adjustable. Just got around to looking at it. Built like a tank was my first impression. Figured out that removing the front or rear panel was necessary to get the top case part to slide off. First thing I notice after opening it up was the upper PCB was out of place and warped. It slides into channels in the two side extrusions. So somebody was in there before me.Then I noticed the LCD display's small PCB was cracked (chunk pulled loose when I unscrewed it from the front panel) and several traces on it where therefore not connected. The LCD appears to be a HD44780 standard 2x20 and I've ordered a replacement. Until it arrives I can't be sure of what error codes may be displayed. But there's other problems, I guess, since the power on LED isn't coming on and seller reported front panel wasn't controlling the output. Tomorrow I'll probe the power supply in the hopes that a voltage is out.

author: Old Don
author_rank: Regular Contributor
timestamp: October 12, 2017, 09:16:55 pm
content: I received my replacement LCD panel and installed it. Powered up the 2711A and the display is working, front panel settings push buttons work and change the displayed settings. I hooked up my nearly 40 year old 600 MHz Davis frequency counter to the main output BNC and couldn't get an output that followed the LCD settings. Guess the next step is to RTFM and make sure I have it set up correctly before assuming that there's more problems to repair.

author: Old Don
author_rank: Regular Contributor
timestamp: October 13, 2017, 10:41:46 am
content: Looks like I need a service manual or at least a schematic! If anyone has one, please PM me! Also, how I can get a copy of WaveWorks Jr. assuming I can repair it and use the RS232 or GPIB connectors.I followed the verification process operators manual holding down the "Local" key when powering it up to clear memory. I hooked the freq counter to the 10MHz reference output on the back of the 2711A and got 10.000150 MHz which was out of spec, but then again my freq counter hasn't been properly calibrated since 1981.However, when setting a 1MHz output in the next step there was no output from the main output BNC.Next step was checking the analog board traces near the output and checked the fuse, which was good. There's a bunch of relays in the area and I could hear a couple cycle when I powered the unit up. Without a schematic It's going to be a pain to test since you need to pull the top digital PCB out to reach the lower analog board to test it. So testing under power is out unless clipping a lead or two to components and reassembling. Then take apart, hook up, reassembly and test a few other points and so on and so on.

author: orbanp
author_rank: Regular Contributor
timestamp: October 13, 2017, 01:26:07 pm
content: Hi Don,You could ask Tegan if they would provide the service manual or schematics:https://www.tegam.com/Good luck, Peter

author: Old Don
author_rank: Regular Contributor
timestamp: October 13, 2017, 08:51:13 pm
content: Peter,I planned on doing that if nobody had a service manual.If I can fix the unit then I'm afraid to ask the price for their remote control software package.I did a bit more troubleshooting and found out that it functions correctly up to 2kHz. Frequency, waveform and voltage all adjust, so basic function of the unit is all there, just not the full output range. Top frequency is 2MHz per user's manual/Tegam sales data. But when in the kHz range and adjusting frequency the display stops dead at 2kHz while using the control knob, but you can raise/lower below that frequency. I think it should auto scale as you tweak the knob. I'm guessing (or hoping) that there's a relay(s) that that should kick in for range change to 10's of kHz that's not working.This weekend is shot - tomorrow I'm attending a veteran burial and Sunday the wife has us visiting some people from her place of work. So Monday I'll be calling Tegam for help.

author: Old Don
author_rank: Regular Contributor
timestamp: October 15, 2017, 01:52:08 pm
content: The 2711A is supposed to operate from 0.1Hz to 2MHz. Playing around with the unit I have I think it has to have been modified (M128) to operate from 100 micro Hz to 2khz.Yes, micro Hz! Cowabunga!Here's my reasoning, if I use the rotary dial to adjust the output frequency I can decrease frequency from 2KHz down through Hz all the way to 101 micro Hz. I can't measure it, but the 2711A's display tracks down without a problem as one turns the dial. But if I start at, say, 1KHz it will track up to 2kHz and stop dead and not allow higher frequencies. The nameplate on the rear has the S/N plus "M128" on a second line which lead me to think the unit might have been customize for extreme low frequencies. Seismic engineering studies?However, not very useful for me.Time to call Tegam!

author: Old Don
author_rank: Regular Contributor
timestamp: October 16, 2017, 06:27:16 pm
content: Called Tegam and got someone that wasn't up to speed on their old stuff. Sent an email follow up as suggested and so far no reply. Doesn't look like I'm going to get good news from them.There's a 2nd 2711A on fleabay that I might buy and compare digital and analog boards between the two to see if it is software, hardware or both that needs to be changed. Else, anyone in need of micro Hz waveforms?

author: Old Don
author_rank: Regular Contributor
timestamp: October 20, 2017, 12:47:32 pm
content: I received an email back from the engineer at Tegam stating that he was waiting on a 2nd person to return from vacation. That person was most likely the last remaining employee that might know about modifications available on the 2711A. So slim chance that I'll be able to get details from Tegam.I'm thinking that if I could compare PCB's to those in a standard 2711A that I could convert this one back to standard too. Software EPROM's read and copied plus whatever hardware changes necessary to change the scaling.Back to other projects such as debugging my Tektronix scope.

author: ElektroQuark
author_rank: Unknown
timestamp: October 20, 2017, 01:02:23 pm
content: Hi Don,No photos?

author: Old Don
author_rank: Regular Contributor
timestamp: October 20, 2017, 01:16:51 pm
content: I guess I could take photo's since this is an uncommon beast. I'll have to disassemble it again to take them. Won't have time today.