[Solved]HP 33120A Function Generator  Power On Problem - Page 1
Forum section: electronics / repair

author: coldframe
author_rank: Regular Contributor
timestamp: October 25, 2016, 09:01:56 am
content: Hello, ForumWhen I power up the 33120A turns on/off all display segments then beep once Apart from anything else, Shift Key Work.EditOf course, Checked a Display Panel Power Rail, Ribbon cable on the basis of the Scmematic (P.141)-13V Supply, -13.4V (Include two 1uF Tantal Caps OK But Replaced New)+6V Supply, 6.1V+18V Supply, 18.1V-18V Supply, -18.3V2.5V Supply, 2.5VThis clip shows a Problemhttps://www.flickr.com/photos/boricha/30438162192/in/datetaken/Here is what Relevant Beeps says on Service manualQuoteAgilent 33120A 15 MHz Function / Arbitrary Waveform Generator Service Guide (33120-90017)http://cp.literature.agilent.com/litweb/pdf/33120-90017.pdfI Guess the probable reason for the "Error 625, I/O processor does not respond "Does anyone has an idea what is wrong , or where should i start?Best regards, coldframe.

author: singapol
author_rank: Frequent Contributor
timestamp: October 25, 2016, 01:33:39 pm
content: Try reseating the connectors in the display panel, that is pull them out and insert back in that it will sort of scrape off whatever contaminants on the pin, other than this as what the manual says check the relevant ICs and components as described.

author: coldframe
author_rank: Regular Contributor
timestamp: October 26, 2016, 03:16:45 am
content: Hello singapol.QuoteWell, I appreciate you, and sharing.Sadly, still the sameI should stop for today.coldframe.

author: TheSteve
author_rank: Unknown
timestamp: October 26, 2016, 03:25:22 am
content: This is a tough one as it fails before it can gives any true error codes.Have you tried communicating with the unit via GPIB?Do any components get unusually warm/hot?I know ram failures aren't uncommon in the 33120A so if you decide to just try replacing parts you might want to start there. It would be much more ideal to have a second unit so you can swap parts to narrow the failure down between the front display and the main board.

author: coldframe
author_rank: Regular Contributor
timestamp: October 26, 2016, 05:07:13 am
content: Hello TheSteve.QuoteGPIB Card, not here right now the week next, the week after next I could doClose by FAN LM2940CT(U1004 ) is Hot but OK(Temeprature Sensor is My finger)There are four SRAM,U105(256K-BIT SRAM 70ns) Floating LogicU205(256K-BIT SRAM 25ns) Digital Waveform Data SynthesisU404,405(256K-BIT SRAM 15ns) Waveform DACif RAM failure, It's U105(256K-BIT SRAM 70-NS) because U105 Control by SCX6206AK0(U103) IC-Gate Ary ASIC(Agilent Part# 1820-8907), What do you think?I use 33120A a long intervals. Second Unit, humm, It's too hard to meAnyway, It hasn't been long since Reading SchematicI still want more time to consider opinions.Thanx TheSteve.coldframe.

author: Jwalling
author_rank: Unknown
timestamp: October 26, 2016, 12:50:40 pm
content: Quote from: coldframe on October 25, 2016, 09:01:56 amWhat about the +5V?I've seen a 34970A with that same error and it was due to the power on reset circuitry, which is very similar to the circuitry on the 33120A.Check U102 pin 16. IS the micro being held in reset?

author: TiN
author_rank: Super Contributor
timestamp: October 26, 2016, 01:01:49 pm
content: My unit has bad U103. Fixed after swap from donor board...

author: coldframe
author_rank: Regular Contributor
timestamp: October 26, 2016, 01:14:17 pm
content: Hello JwallingQuoteDp you mean U1002(MC78L05ACD)? Yes It's okI'm out of town Now, I'll check U102 pin 16 later.How did you manage the Your problem?Hello TiNQuote from: TiN on October 26, 2016, 01:01:49 pmHow did you know U103 dead?If it's a question of U103 Maybe I can find a Second Hand chip.U103 IC GATE-ARY CMOS Mfr. Part# SCX6206AK0, Agilent Part# "1820-8907"34401A U501 also "1820-8907"Thankscoldframe.

author: TiN
author_rank: Super Contributor
timestamp: October 26, 2016, 02:39:42 pm
content: Output on my ARB was garbled, giving random signals, so I replaced bunch of ICs around, SRAMs, checked DAC, checked firmware ROM, margined with power, but all was for nothing. Then I bought second 33120A board, swapped U103 it got fixed right on. I still has that spare board without chips

author: Jwalling
author_rank: Unknown
timestamp: October 27, 2016, 10:22:20 am
content: Quote from: coldframe on October 26, 2016, 01:14:17 pmNo, I mean VCC which comes from U1004, a LM2940.Quote from: coldframe on October 26, 2016, 01:14:17 pmI've seen the problem on more than one 34970A. In one case it was a bad 34064 undervoltage sensor chip. That would be U1052 on the 33120A in the power supply schematic.Other error 625s from my 34970A repair logs - maybe you can correlate to the 33120A using a 34970A schematic:1. U302 74HCT132-1 (schematic page 3 of 4) pin shorted internally.2. Fan not running unless I PRESS DOWN ON THE pcb. U303-5 (GND for one of the optos; signal = ER_OPDO ) had a fractured solder joint.

author: coldframe
author_rank: Regular Contributor
timestamp: November 06, 2016, 08:32:28 am
content: Hello ForumI'm sorry that my Feedback is so late, I have made a business trip.TheSteve, Jwalling,Quote from: TheSteve on October 26, 2016, 03:25:22 amQuote from: Jwalling on October 27, 2016, 10:22:20 amThe above image> The GPIB isn't working.The above image> measured U1004(LM2940) Voltage, Current, TemperatureVoltage : In:9.9V, Out:4.9V, Current : 900mA, Temperature : Almost 80C (Fan Not Connected)Voltage is Looking Good but Current & Temperature That seems to be the problem.LM2940x 1-A Low Dropout Regulatorhttp://www.ti.com/lit/ds/symlink/lm2940-n.pdfTin,Quote from: TiN on October 26, 2016, 01:01:49 pmI switched U103 to where good 34401A(U501) was and vice versa. no change in the patient’s conditionI need to do more investigation. I welcome any comments you may have.coldframe.P.SI'm Information Technology EngineerBUT, collecting firewood better than My jobSafety First.

author: Jwalling
author_rank: Unknown
timestamp: November 06, 2016, 10:53:09 am
content: You haven't checked to see whether the micro is being held in reset yet?

author: EE-digger
author_rank: Frequent Contributor
timestamp: April 22, 2018, 03:21:23 am
content: Late arrival to this thread but it just brought life to my "new" 33120A.It exhibited the all segments on, then off, then one or two beeps, then only the shift key responds, indicating that the display processor is running.There was no clock or data activity on the display cable.Thanks to JWalling's posts, I targeted the power on reset chip, U1006, and found 2.3V at its output. In a lazy attempt to force the pin, I shorted it to the adjacent pin at 5.0V with my scope probe tip. After doing this a few times, the unit started to power=up properly.My assumption at this point is that one of the two caps sitting on the reset line were bad, pulling the line down. My application of 5V may have "opened up" the damaged cap.If the problem resurfaces, I'll replace those caps and maybe U1006 itself.

author: mzzj
author_rank: Super Contributor
timestamp: May 14, 2022, 05:41:49 pm
content: Had somewhat similar adventure that started 6 years agohttps://www.eevblog.com/forum/repair/help-anyone-have-hp-33120a-function-gen-rom-firmware/one beep on power up and only shift key/announciator works on front panel.U102 main mCU PONRST (reset) was low, checked voltage supervisor U1006, output high so something else is pulling the PONRST low.on oscilloscope PONRST is sawtooth-looking signal approx from 1...2 voltsReset on 80C196 MCU is bi-directional so pull PONRST pin from U102 mCU --> PONRST no longer pulled down -->Suspect U102 not happy about memory content, clone and flash U104 EPROM and U106 Flash chips from working unit --> no improvementReplace U102 80C196 mCU --> no improvement.Replace U103 ASIC --> no improvementSwap U105 SRAM from working unit to UUR(unit under repair)working unit now dead (turns out I soldered U105 upside down)previously non-functioning unit turns on and works but I get error 625turns out OP_RXD* to U103 ASIC is not properly soldered, resolder the pin to board and UUR is workingWould have been lot easier to replace the U105 SRAM right away

author: free_electron
author_rank: Super Contributor
timestamp: May 16, 2022, 04:20:06 am
content: i've seen multiple reports of the rams failing.

author: coldframe
author_rank: Regular Contributor
timestamp: May 16, 2022, 02:01:17 pm
content: Yes!In My case U105 SRAM Fault.