|
Vintage Television and Video Vintage television and video equipment, programmes, VCRs etc. |
|
Thread Tools |
24th May 2022, 6:36 pm | #1 |
Tetrode
Join Date: Dec 2017
Location: Bath, Somerset, UK.
Posts: 71
|
Help fixing Hitachi B & W monitor needed.
Hi Chaps,
I have an old black and white monitor from my Space invaders arcade machine that I just can't figure out what is wrong with it. I have checked every component, wire, connection. Unfortunately there are no schematics available for it. I started a thread over on KLOV https://forums.arcade-museum.com/thr...onitor.506109/ Which has come to a dead end. I'm sure there are some experts on here that could figure out the problem. I have HV, brightness and contrast controls don't do anything and I have no picture. I accidently managed to make a picture appear by having my meter set on ohms and touching Pin 7 ( Cathode on the CRT) this brought up a picture as seen here https://youtu.be/X8vD7Ks6rhU Chassis can be seen here https://youtu.be/4w7D0_O16oQ I have an impedance/resistance meter, a semiconductor tester and an ESR meter. I am pretty sure I have check every component. Any help would be much appreciated. I have never seen the monitor work, I purchased the game as a non worker. |
24th May 2022, 6:55 pm | #2 |
Dekatron
Join Date: Jun 2009
Location: Staffordshire Moorlands, UK.
Posts: 5,263
|
Re: Help fixing Hitachi B & W monitor needed.
where's the child on the bike come into it?
__________________
Kevin |
24th May 2022, 6:58 pm | #3 |
Tetrode
Join Date: Dec 2017
Location: Bath, Somerset, UK.
Posts: 71
|
Re: Help fixing Hitachi B & W monitor needed.
That was an video tape in a VHS player I was using for composite input
|
24th May 2022, 7:04 pm | #4 |
Dekatron
Join Date: Jun 2009
Location: Staffordshire Moorlands, UK.
Posts: 5,263
|
Re: Help fixing Hitachi B & W monitor needed.
Looks like the tube is cut off, can you tweak the A1 up? I assume the monitor is actually designed for 1V video rather than modded to accept TTL (I've seen them before you ask).
__________________
Kevin |
24th May 2022, 7:09 pm | #5 |
Tetrode
Join Date: Dec 2017
Location: Bath, Somerset, UK.
Posts: 71
|
Re: Help fixing Hitachi B & W monitor needed.
A1, would that be G1? It's tied to ground via a 33k resistor.
|
24th May 2022, 7:11 pm | #6 |
Tetrode
Join Date: Dec 2017
Location: Bath, Somerset, UK.
Posts: 71
|
Re: Help fixing Hitachi B & W monitor needed.
I get 130v to 164 on pin 7 Cathode depending on brightness pot position. 1 and 8 are heater. Pin 2 G1 tied to ground. Pin 3 43V, Pin 4 focus 0 to 366 volts depending on pot position.
|
24th May 2022, 7:13 pm | #7 |
Tetrode
Join Date: Dec 2017
Location: Bath, Somerset, UK.
Posts: 71
|
Re: Help fixing Hitachi B & W monitor needed.
The monitor model is an MCL-461F. I have searched everywhere for a schematic.
|
25th May 2022, 7:17 am | #8 |
Octode
Join Date: Feb 2007
Location: Ely, Cambridgeshire, UK.
Posts: 1,967
|
Re: Help fixing Hitachi B & W monitor needed.
a hunt round the web found circuit HITACHI CHASSIS MCL-437F MCL437F MCL 437 437F
which may be close and help google search for download |
25th May 2022, 7:39 am | #9 |
Tetrode
Join Date: Dec 2017
Location: Bath, Somerset, UK.
Posts: 71
|
Re: Help fixing Hitachi B & W monitor needed.
Thanks, that has been discussed before on another forum and unfortunately it's not similar.
I do know someone with a working chassis, I'll ask him to take some voltage readings at the neck. |
25th May 2022, 10:28 am | #10 |
Dekatron
Join Date: Apr 2012
Location: Worksop, Nottinghamshire, UK.
Posts: 5,549
|
Re: Help fixing Hitachi B & W monitor needed.
There may be some value in looking for the tube data sheet.
The resistance range experiment is already telling us it is a static voltage problem in the tube biasing circuit. At one time when they were worth repairing I used to repair computer screens with circuit diagrams being rarer than rocking horse manure. |
25th May 2022, 1:14 pm | #11 |
Dekatron
Join Date: Jun 2009
Location: Staffordshire Moorlands, UK.
Posts: 5,263
|
Re: Help fixing Hitachi B & W monitor needed.
Looks like the cathode volts may be a little high, especially as shunting it to chassis with your meter (poor meter) brings a raster up. ie it's cut-off. As per previous post I suspect a standing voltage, some of the resistors might be quite high values that are good at going open as they age. Could also be the video transistor (usually a pair, a big one and a little one) as I'm guessing its cathode drive. Examine all the joints around the heat-producing parts, tube socket pins, etc
__________________
Kevin |
25th May 2022, 1:29 pm | #12 | |
Tetrode
Join Date: Dec 2017
Location: Bath, Somerset, UK.
Posts: 71
|
Re: Help fixing Hitachi B & W monitor needed.
Quote:
|
|
25th May 2022, 1:32 pm | #13 | |
Tetrode
Join Date: Dec 2017
Location: Bath, Somerset, UK.
Posts: 71
|
Re: Help fixing Hitachi B & W monitor needed.
Quote:
Yes it’s a poor meter but I like that it uses voice to read out the measurements, so you can keep your eye on the probes I’ll reflow any solder joints that may heat up and see if that makes a different. |
|
25th May 2022, 7:08 pm | #14 | |
Tetrode
Join Date: Dec 2017
Location: Bath, Somerset, UK.
Posts: 71
|
Re: Help fixing Hitachi B & W monitor needed.
Quote:
Tube is a 500 ZB4, I'll see if I can find something on it. This Tube is the same as the ZB4 https://tubular.atomized.org/tube/500NB4 |
|
25th May 2022, 7:14 pm | #15 |
Heptode
Join Date: Jan 2011
Location: Croydon, London, UK.
Posts: 766
|
Re: Help fixing Hitachi B & W monitor needed.
The voltages you are measuring around the tube base are not what I would expect for a typical CRT.
You have measured: Cathode (Pin 7) 130-164V depending on the brightness control setting. The 130V should correspond with the fully clockwise brightness adjustment. G1 (pin 2) = 0 V - tied to ground via a 33k resistor G2 (pin 3) = 43V Focus (Pin 4 ) 0 to 366V depending on setting of the focus control. I have looked for a datasheet for the tube that is used in the monitor, without any success. Toshiba has a range of tubes of the same size, which may give some idea as to what the voltages should be. They quote typical values as follows: Focus 0-400V G2 400V Raster cut off voltage ( g1 voltage - cathode voltage) -36 to -94V. Based on this, your G2 voltage is far too low. It will be fed via a high value resistor from a high voltage point, The resistor may have risen in value (or your meter really is terrible and is loading the voltage!). Either your cathode voltage is too high, or your g1 voltage is too low. It's not unusual for g1 to be biased to a few 10s of volts, so have a look for any other resistors connected to g1. On another forum you reported some voltages from transistors in the video amplifier stages. It would help others here if you could report the voltages here. Paula |
25th May 2022, 7:22 pm | #16 |
Tetrode
Join Date: Dec 2017
Location: Bath, Somerset, UK.
Posts: 71
|
Re: Help fixing Hitachi B & W monitor needed.
|
25th May 2022, 7:27 pm | #17 | |
Tetrode
Join Date: Dec 2017
Location: Bath, Somerset, UK.
Posts: 71
|
Re: Help fixing Hitachi B & W monitor needed.
Quote:
G1 is tied to ground via a 33k inline resistor. G2 does look low though, I'll trace it back from the cable and double check resistors/capacitors. I'll paste some info from the other thread on here. |
|
25th May 2022, 7:30 pm | #18 |
Tetrode
Join Date: Dec 2017
Location: Bath, Somerset, UK.
Posts: 71
|
Re: Help fixing Hitachi B & W monitor needed.
Funnily enough the 1 bad electrolytic I found was on the G2 circuit (315v 1uf) Maybe that fried something further back.
|
25th May 2022, 7:39 pm | #19 |
Tetrode
Join Date: Dec 2017
Location: Bath, Somerset, UK.
Posts: 71
|
Re: Help fixing Hitachi B & W monitor needed.
https://www.trutechtools.com/iDVM510 My meter
|
25th May 2022, 9:43 pm | #20 |
Tetrode
Join Date: Dec 2017
Location: Bath, Somerset, UK.
Posts: 71
|
Re: Help fixing Hitachi B & W monitor needed.
Well I checked every resistor, every cap and transistor in that section and they all check out ok. damn thing. Flyback issue?
|