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Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets.

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Old 20th Nov 2020, 12:37 pm   #21
Refugee
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Default Re: Help with a component ?

Your AC will be at chopper frequency.
You will need to unplug the chopper unit and check the heater for continuity with a DMM.
Older ones that had a couple of turns on a 50hz mains transformer were easy to check but an open circuit filament is still the most likely fault with heaters on these kind of displays.
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Old 20th Nov 2020, 1:23 pm   #22
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Default Re: Help with a component ?

Thanks again for your help with this .I'm afraid you'll have to help me identify the 'chopper' .. the only one I know was the bike I used to dream of owning but never did when I was about 10.... and how do I test for continuity in the heater ... I would presume from the schematic that its between the two outer pins on each side of the display screen ... as that's where it shows the 0.5vac .?
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Old 20th Nov 2020, 1:35 pm   #23
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One other thing just in case it helps ... I looked at the remote with the camera and it works fine however it doesn't switch on or off the unit ... the sensor i guess is probably on the same circuit as the display .. don't know if that helps anything.
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Old 20th Nov 2020, 1:51 pm   #24
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Default Re: Help with a component ?

I've been searching on the net and now presume that the chopper you're referring to is the DC-DC converter on the board under the display... if this is the case it's a 10 pin round component... do I have to un-solder and remove it ?
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Old 20th Nov 2020, 1:56 pm   #25
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Default Re: Help with a component ?

Quote:
Originally Posted by Drewpicker View Post
I've looked at the schematic and it appears that the two outer pins should effectively have 0.5vAC ... however when I test them they measure at -20.3vdc .. I'm testing with negative clipped to the chassis (hope that's right) they appear to be supplied from pins 7 and 9 of the dc to dc transformer.. could it be that this has gone and they are shorting to pin 8 ... thus sending -20.3vdc instead of 0.5vac ?
These displays are like a directly heated valve....no separate cathode so the filament is the also the cathode. Because of this, a negative bias is applied to the filament, just like a directly heated valve so don't worry about the negative DC voltage you are seeing on the filament. There should be a voltage of about 3 volts across the filament....exactly where this is derived from depends on the circuit you have but I think it should be more than .5V! There is usually a DC-DC converter that supplies an 'HT' of around 30V which is sufficient to allow the segments to glow.

My experience with these display circuits is with my battles with Akai video recorders back in the 80's and 90's where a repair kit was supplied for the DC-DC converter comprising of a couple of diodes, a couple of electrolytics and (doing this from memory) possibly a transistor and resistor as well to replace the fried components.

I suggest you have a good look around the DC-DC converter circuit particularly at any electrolytics that will probably have led a hard life, in fact anything around the display chip to do with the negative bias as well.
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Old 20th Nov 2020, 6:01 pm   #26
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I've tried testing the filament in line and got 0v .. theres an electrolytic that I measured in circuit at 52uf and i think it's got a high esr value..it should be nearer 100uf but because it's in circuit I don't know if the capacitance is tired .. I tried to un solder it to swap it out but it's seated in a plastic case that seems to be stuck firm to the pcb and likewise the cap so its proving difficult to extract ... I have no more time today but I'll get onto it tomorrow with some better tools ... thanks to you both for all the help... have a good Friday night .
Andrew .
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Old 20th Nov 2020, 7:59 pm   #27
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Default Re: Help with a component ?

you say "I've tried testing the filament in line and got 0v .. ". Sorry this makes no sense. To test the filament (preferably with one feed disconnected) you measure its RESISTANCE. Everything switched off of course.
I am not that familiar with these, but if it is working, there is a good chance you could measure that 0.5v or whatever it is by connecting your meter probes across it with meter set to AC volts. If it is a high frequency square wave, this may not work, in which case you need an oscilloscope with a the two channels operating in ADD mode, with one channel inverted. If you don't have a decent scope, ignore that.
Les.

Last edited by MotorBikeLes; 20th Nov 2020 at 8:00 pm. Reason: remove errant 2.
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Old 21st Nov 2020, 4:46 pm   #28
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Default Re: Help with a component ?

Can you post a better (larger) picture of the circuit in post #20? Difficult to see but there are diodes providing bias (I think) that might need checking. I suppose that 0.5 on each filament pin could be correct as it would give 1.0V across the filament. You might be able to see the filament glow in a dark room (and I mean dark) if it is in fact working at all. It will appear as a number of fine lines glowing faintly across the front of the display. If there is a filter in front of the display, this should be removed or you won't see the glow at all.
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Old 22nd Nov 2020, 4:59 pm   #29
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Just a quick update to keep you informed ... I decided to swap out the cap c202but as I posted before it was proving difficult ... it does have a high esr value however some of the board came away with it on both feet .
. I guess the only way to take one out properly is if you have a blower heater thing as it turned out to be surface mounted on the plastic frame with one side connected to the other side of the board via solder ... I'm busy trying to repair this mini catastrophe.... I'll post a clearer schematic of the display board and when I've put the new cap in I'll check in the dark ... thanks for your patience with this ... Andrew
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Old 23rd Nov 2020, 4:41 pm   #30
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Default Re: Help with a component ?

Hi ... got the cap in but no change .. I'm waiting till it gets dark tonight to have another look if there's anything but from what I can see there's nothing at all.
Hi Les ... when I said in line I meant across it .. ie one probe of my dmm on each side of the display ... 0v.

The easiest way for me to isolate the filament would I believe to snip one pin going to the board from the display. I don't have an oscilloscope but would love to get one maybe in the future... they seem to be highly useful tools . I Have a DMM and a BSIDE ESRpro02.

Here are the pages with the schematic and board layouts I've managed to combine them into a pdf .
What's the best way to move forward on this ?
All the best .... Andrew
Attached Files
File Type: pdf Display sony_rdr_dc205.pdf (519.9 KB, 7 views)
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Old 23rd Nov 2020, 7:49 pm   #31
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Default Re: Help with a component ?

OK, I understand now how you had your meter connected, but was it switched to AC or DC? Clearly it is not a DC voltage across it, but a square wave AC one (if actually present). If it is a very high frequency, your meter may not see it, but it is likely that something will be registered.
Les.
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Old 24th Nov 2020, 12:16 am   #32
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Just tried again ... and you're right ...I'm getting 1.6v ac and have checked the filament in pitched black and I see it lit from one side to another very faintly but clearly visible... I unplugged the unit to be sure it wasn't some fluorescent light I was seeing and it immediately went out ... upon plugging back in I am now getting 1.9vac to 2vac .... it had been plugged in a while before the first reading ..
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Old 27th Nov 2020, 4:33 pm   #33
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Hi Anyone got any ideas how to proceed with this , I've been in limbo for the past few days and have no idea where to look next .... I could just scrap it and recycle as much as I can see as useful ... but that seems a shame if there's a way to get it working again ... all the best .. Andrew
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