Hp 54501  CRT problem need help - Page 1
Forum section: electronics / repair

author: Brainsysnet
author_rank: Newbie
timestamp: September 22, 2017, 06:19:21 pm
content: HiI am new in this blogI going to buy hp 54501A osciloscope from ebayBut have loo like crt problem , i am not sureCan someone help me , what is this problem . You can see the picture

author: oldway
author_rank: Super Contributor
timestamp: September 23, 2017, 06:35:43 am
content: Hello, welcome to the forum.No this is not a CRT problem.This oscilloscope is a digital oscilloscope.To better understand the complexity of this oscilloscope, here is a video of Dave on the subject.I strongly advise against buying this oscilloscope, your diagnosis demonstrates for sure that you are not an "expert" in oscilloscopes.

author: vk6zgo
author_rank: Super Contributor
timestamp: September 23, 2017, 10:39:54 am
content: Quote from: oldway on September 23, 2017, 06:35:43 amFrom the pix, it seems to have a CRT tube as a display device.To me it looks like a raster type display, just because of the appearance of the interference, but I may be wrong, as from memory, most of that style of DSOs used a vector type display.

author: TK
author_rank: Super Contributor
timestamp: September 23, 2017, 11:58:42 am
content: It might just be bad capacitors on the CRT module. I think the 54501 uses a Hitachi CRT module as in many old HP equipment. I saw several 54501 scopes on eBay at very low prices that seem to be in better shape.

author: Retep
author_rank: Regular Contributor
timestamp: September 23, 2017, 12:45:24 pm
content: Quote from: oldway on September 23, 2017, 06:35:43 amThis is a digital oscilloscope with a CRT. Considering there are retrace lines on the photo of the (raster) CRT, it is reasonable to assume that something related to the CRT, or the CRT itself, is broken. It might be that the CRT is driven incorrectly, which in turn might be caused by a bad power supply, which in turn might be bad caps or there might be a problem with the circuitry driving the CRT or the CRT itself might be broken. Considering that besides the retrace lines there also appears to be something like vertical hum bars on the CRT, I would first check the power supply and the caps on the power supply lines or the CRT module. Though photos like the one posted are helpful, it is near impossible pinpoint the exact component that causes the issue with just that, unless it is a very common/known issue of the device.The problem with repairing oscilloscopes is that in many cases you will need a working oscilloscope to repair it. Unless this scope is extremely cheap (< 50 USD) and you enjoy repairing stuff, I'd skip this one.

author: Bushougoma
author_rank: Regular Contributor
timestamp: September 23, 2017, 12:58:02 pm
content: If you want a budget 100 MHz digital HP scope go for the 54645D or 54645A they have the Megazoom ASIC, the user interface is very intuitive and bug free, and they boot up almost instantly (within seconds of power on). I'd go for the D version personally which has a built in 16 channel logic analyzer the A version has an external trigger BNC in place of the logic analyzer.You may have to replace the Dallas NVSRAM that holds the calibration constants and the user settings if the internal battery has died. But these scopes have a self calibration function so loss of cal data is no big deal.

author: TK
author_rank: Super Contributor
timestamp: September 23, 2017, 01:13:55 pm
content: +1 for the 54645D or 54645A

author: vk6zgo
author_rank: Super Contributor
timestamp: September 23, 2017, 03:02:29 pm
content: Quote from: Retep on September 23, 2017, 12:45:24 pmIt is most unlikely to be the Cathode Ray Tube itself which is faulty.Tube faults do not usually manifest themselves in such a manner.Usually, a faulty tube is either lacking in brightness, completely dead, or cannot be focused correctly, even though the Electronic circuitry to do so is not faulty.Another confusing factor is that "Computer people" have an annoying habit of referring to the whole "monitor" unit as a "CRT", so we do not really know what the OP meant.This is similar to the way people in earlier years referred to cars as "motors", & transistor radios as "transistors".

author: TK
author_rank: Super Contributor
timestamp: September 23, 2017, 04:29:31 pm
content: Vintage HP test equipment use a lot of Hitachi CRT module with different branded tubes. I repaired several "CRT modules" that had bad capacitors. But the fault on the original picture looks like it can be coming also from the CPU board (maybe bad video RAM?), or it can also be another case of bad capacitors. The boards I repaired had different symptoms, like shrinking images, flickering video, burned fuse, big explosion and no video, etc.