Fluke PM3394B CRT replacement - Page 1
Forum section: electronics / repair

author: Krisztián
author_rank: Contributor
timestamp: January 16, 2022, 11:08:21 pm
content: Good day guys!Does the 3394B has the same CRT as the 3370B?I would like to replace the CRT in a 3394B.I found a PM3394B here in Hungary for around 190USD. Badly yellowed (Hydrogen Peroxide & UV might help), needs calibration (cursors are vertically off), and likely changing of electrolytic capacitors required (slightly blurred screen, cannot focus well). Calibration runs without problem, however after a hour some traces shifts by about 1mm from GND. Self test passes. It has GPIB, Math+ and Extended Memory options, newest firmware. No optional BNCs at the back.I think the price is not bad, but the screen has a burn-in! This burn (at least for me) is serious as it can be seen clearly. It's about 2mm wide horizontal line exactly at the center line. It's probably a device that was used by careless technicians 0-24 in industry with high brightness in digital mode.Thanks in advance for your answers!

author: Krisztián
author_rank: Contributor
timestamp: January 16, 2022, 11:16:07 pm
content: Another photo attached.

author: srb1954
author_rank: Super Contributor
timestamp: January 17, 2022, 07:19:58 am
content: The burn-in doesn't look to bad to me. The trace intensity isn't degraded very much in the burn-in area so I would describe the problem more as a minor nuisance rather than a serious defect.However, the trace focus is terrible. The PM3394B should be capable of a much sharper trace that what is shown in your pictures.

author: coromonadalix
author_rank: Super Contributor
timestamp: January 17, 2022, 12:14:10 pm
content: Same toughts here, maybe try to refocus the crtnormally on any crt based equipment there is an focus adjustment on the flyback circuitry, or a piece near it normally the word ''focus'' is written on itBe careful, some flyback have 2 pots on them, and you can mess a few thingsTry to find the service manual, youll be able to find itOr some people here can help, or take and show us some ictures

author: grumpydoc
author_rank: Super Contributor
timestamp: January 17, 2022, 12:20:25 pm
content: Quote from: Krisztián on January 16, 2022, 11:08:21 pmI'm pretty certain that the CRT is different in the 200MHz 'scope compared with the 100MHz one (for one thing, if memory serves the deflection plate connections come out on the base for the 100MHz tube, whereas it's separate connections on the sides/top/bottom on the 200MHz tube.)

author: HighVoltage
author_rank: Super Contributor
timestamp: January 17, 2022, 12:26:08 pm
content: Yes, I can confirm that the high speed tubes (200 MHz) are different from the low speed tubes.The focus can be adjusted in the service and calibration menu, after entering the 5 PIN code.

author: wn1fju
author_rank: Frequent Contributor
timestamp: January 17, 2022, 12:32:31 pm
content: By the way, my similar PM3390B has the same small baseline drift after an hour or so.

author: HighVoltage
author_rank: Super Contributor
timestamp: January 17, 2022, 01:20:40 pm
content: Quote from: wn1fju on January 17, 2022, 12:32:31 pmA small baseline drift should always disappear if you run the Auto-calibration once or twice.(Hold CAL button for 2 seconds)

author: Shock
author_rank: Super Contributor
timestamp: January 18, 2022, 05:59:48 am
content: Looking a part numbers in service manuals is a good way to see if the same parts are used across a series. As mentioned be absolutely sure it's not an adjustment issue or component value drift. Unless it has unmistakable burn in where you can see ghosting when the image is absent or at low contrast then it's more likely just adjustment.