Panasonic VP-5564A 40MHz Analog Oscilloscope need help repairing - Page 1
Forum section: electronics / repair

author: HoangLong
author_rank: Newbie
timestamp: August 03, 2023, 05:51:50 pm
content: Hello. I am a beginner in electronic and I recently bought my first oscilloscope for around 40$ online. Where I live 20MHz scopes usually go for >50$ so I thought I finally struck a deal after a long time searching for a reasonable priced one. The scope arrived in pretty rough shape with stains and scratches. The frame suffered some substantial warping. I opened it up, bent the frame back into shape and here are the pictures of the boards:top view sweep and crt:https://drive.google.com/file/d/1f2u9CtpQLlLoZlZc4CKBQzAdpaBw0Tzw/view?usp=sharingbottom view power and main:https://drive.google.com/file/d/1MKlcYHLsCgRpECMrzXc0zSBkLDXRBZM9/view?usp=sharingside view:https://drive.google.com/file/d/18la6A0Qcj5jCSmeKxZRmdQi5SIsMVhZE/view?usp=sharingback view:https://drive.google.com/file/d/13KIB26TSu6qpYAkWmk4uIyKEiRS0lJA7/view?usp=sharingfront view:https://drive.google.com/file/d/1yPYzW7XupwYRTHagB6jzayBBTltd6BRW/view?usp=sharingI did a close inspection and found the boards look good with no signs of previous tampering or repairing. No cracking or physical damage. Caps look good as new. Solder joints also good. But there were soot on the board at 4 locations. Possibly due to high temperature burned the exess flux which were present on the board. Does anybody know why the soot are there? Is it related to the problem?On case:https://drive.google.com/file/d/17uPg_KaqksqnhwTeyBRd9S8OqUw_gc_Z/view?usp=sharingSweep board:1 screen illuminate drive transistor:https://drive.google.com/file/d/1jFFLxyMv--5z99mJlX-WrtM-uZG-_VAR/view?usp=sharing2 transistor pairs near x- x+:https://drive.google.com/file/d/1lqwrv_OuXQK9rWbBFoQKW1E1jdE_mdXq/view?usp=sharingMain board:3 transistor near HV transformer:https://drive.google.com/file/d/1Cbvckm1XWdKnd43c95oRkFnFR4p83Bxh/view?usp=sharing4 transistor pair near HV transformer:https://drive.google.com/file/d/1BzoajhBqM2-a7ycuEcPcn7-mhqv0MBge/view?usp=sharingThen I powered it up. The power LED turned on but there was no trace visible no matter how I change the settings. Giving it an input still nothing. So I started measuring voltages on the CRT pins. Heres the pictures of the CRT and where its HV pins go on the "main" board:https://drive.google.com/drive/folders/1-jhaifzvQqwSmiOycKnOfj9a3lT1u0TM?usp=sharingWhen I put my probes bettween pin 4 and 3, the screen flashed a slim vertical rectangular for like 0.1s. I started touching the pins repeatedly and the rectangular moves at time/div rate in a straight line even with a square wave on the input. I clipped my MM's COM to the chassis and started probing pin 4 it read -166v. I think pin 3 is the cathode with negative several thousands of volts and I don't have the tool to probe it so I moved to pin 2. The magic happened when I probe pin 2. The moment I touch it with my red probe, an audible spark arced between it and my probe. Then the CRT comes to life displaying a bright dot. The scope was in XY mode. So I changed the time/div knob and fortunately the dot traced as it should but only in a straight horizontal line. Video:https://drive.google.com/file/d/1bYcPiSPNaNvrAFMVheyLv9dN0_8ECtwl/view?usp=sharingI continued by measuring voltages on the main board at the bottom and testing functionalities:VoltagesThere are test points on the board with silkscreened voltage nearby. Most of the voltages were spot on with the exeption of three 11.9v/12v on top right corner looking from backside and one 148v/145vFocusBarely changes anything. Dot went from a squashed vertical to squashed horizontal. Line from kinda sharp to a little wide. Also the texture seems wierd. I never use or even see an oscilloscope upclose before so I can't tell if this is normal:https://drive.google.com/file/d/1qRCA11rYYmKxbS8-N0C7r8q3SHzEk_ps/view?usp=sharingIntensityNothingRotationWorks flawlesslyHorizontal positionWorks flawlesslyVertical positionDoesn't workSignal respondI used an alligator clip and a 1M resistor to hook CH1 to calibration stud. After changing the settings to appropriate values (0.1v/div, 1ms/div), the trace is still the same - a horizontal line. Trying all the settings doesn't make it have any vertical deflection at all. Only horizontal deflection change correctly. Same with CH2.TriggerSeems to work correctlytime/divworks correctlyvolts/divI can see some change in the horizontal lineB delayed sweepSeems to work correctlyI think the horizontal circuit works well but the vertical is damagedCH2 knob is damaged and have problems turning. Is the attenuators behind this knob?Heres a closeup view of the boards:https://drive.google.com/drive/folders/1WZGJJIdCsww6dBs94LbrGXHJIKFVPBNT?usp=sharingCan I have some help please. I have searched the entire Internet for a schematic, service manual or anything. I've even asked ebay, yahoo sellers, repair services,... and got nothing. Should have research well before I made my purchase but I was too exited. Any help will be priceless for me. I have been working on this for more than 10 days now. Also if you have any advice, please say it. Thank you!

author: Wallace Gasiewicz
author_rank: Super Contributor
timestamp: August 03, 2023, 08:44:32 pm
content: Finding information for most Panasonic gear is almost impossible.Since you had some results probing the cathode ray tube itself. Maybe disconnect it and clean the pins.Clean and resolder the pins at the board also.Also sometimes the pins themselves become disconnected. The leads out of the glass envelope are soldered to the pins and sometimes this solder becomes corroded and can be fixed by melting and removing the old solder and applying new solder to the pins. I don't know if this is the type of CRT construction you have, I did look at you pictures and I cannot tell. If you try this, it takes quite a bit of solder to fill the pins.You can check the CRT but it requires an TV Tube tester and you have to make an adaptor to conform to the pins.Without any schematics, I fear further work is going to be hard.Most lack of vertical is usually caused by burned out inputs, whether this is the attenuator or most likely the input transistor which is usually a FET, but yours does not even move with the vertical adjust.

author: HoangLong
author_rank: Newbie
timestamp: October 15, 2025, 04:03:45 am
content: I've fixed the oscilloscope. Here's what I found:The paralysed vertical movement:I followed the signal from the input BNC the output and found cracked solder joints in both final power transistors in the vertical output amplifier. They are mounted on the chassis for heat sinking and was stressed in shipping.Intensity stuck at max:I checked for any output in the Z axis output amplifier and it was missing. I found a very similar schematic but with different part ID which also used 4 D668 NPN transistors:manualsplus_00385.pdf(5562.13 kB - downloaded 1 times.) (page 67)The Q822's base was at -6V, while R886 was only dropping 0.4V. Which led me to believe R884 had a much higher resistance than 47k because it dropped 145V at ~1.2mA. I took it out of circuit and measured it, it was spot on at 47k. I took my soldering iron and heated it up but its resistance still unchanged. Troubled, I build up the circuit in a simulator (https://tinyurl.com/26xlk45v) and increased R884 and R887 to ~100k, and I saw the same values from my real measurements. Then I replace both R884 and R887, and Q825, Q826 just to be sure although I don't think the transistors had any problem. That fixed it. Anyone knows why both of the resistors R884 and R887 increased their resistances in-circuit, but not under heat?Here's a helpful post that helped me. Thank you to the author!https://hirokun.jp/av/vp-5020a.html