Help with a component ?

[Drewpicker]

Hi anyone .... I'm trying to find an equivalent for this component... in the service manual its listed as a
DSP-501N .. which seems to be some kind of surge absorber... when I plug the mains lead in a spark across it can be seen... looking on the net it talks about "spark over " on the data sheet ...so maybe this is normal but I've never seen that on anything before and it looks to be damaged (see photo) ... its PCB number is Z101 .. which I thought should be the notation for a zenner diode .

It comes from an old Sony HD recorder RDR -DC205 that has lost the front panel display when I turn it on .

I cant find one to replace it (the DSP-501N) ... it was made by Mitsubishi apparently ... is there a common equivalent? ... How can I test this ? ... is there any way I can use another component or modification to get around it ...

Thanks in advance for any help with this ... D

[Refugee]

In short it is a spark gap and is in working order.
There is a scuff mark on the green paint band that will not effect operation in any way.

[Drewpicker]

Thanks R ... I'm originally from across the way from you ... Ecclesfield.. North Sheffield...I was hoping that might be the problem and an easy fix ....I've put it into the service mode and I get the menu on the tv but can't access the display panel via the remote as the display stays off and i get no infra-red to select any of the options ...so I guess there's a problem in the power supply to that part of the circuit ... there's nothing obvious blown on that so i should maybe start a post in another part of the forum to see how I'd go about finding the fault ... thanks for your help .

[Philips210]

Hi.

I think it's a type of glass gas discharge tube. I may be wrong, but it looks like the inside of the glass has a black deposit possibly due to arcing.

Regards,
Symon

[Philips210]

Hi.

There is some information here: https://www.mmc.co.jp/adv/dev/englis...rge03/dsp.html. Mitsubishi call these surge absorbers. The DC spark-over voltage for the DSP-501N is listed as 500V.

Regards,
Symon

[Refugee]

The black deposit looks like dust on the outside to me.
The scratched green paint will be the 5 for 500 volts.
Have a close look for a getter in the VF display and check the continuity of the heater in it too.

[Diabolical Artificer]

These shouldn't ordinarily spark should they? They should only spark under a fault condition.

A

[Radio Wrangler]

Originally Posted by Diabolical Artificer

These shouldn't ordinarily spark should they? They should only spark under a fault condition.

They aren't simple spark devices, there will be low pressure gas inside the glass (sometimes ceramic) casing. They will flash over under events like mains transients or ESD events, depending on what they're being used to protect.

They can absorb a specific amount of energy per transient, based simply on their thermal mass and the temperature they can withstand.

A 500v transient clipper is only part of the defence mechanism. Its job is to take the worst of the transient. Gas discharge devices are fast and have a good energy to size ratio. But one like this leaves 500v of the transient to be absorbed by secondary defences in order to get the transient reaching tender devices sufficiently suppressed.

One elephant in the room is that they're only good for a limited number of zaps before their trigger voltage starts to creep upwards.

It's a bit like class-X capacitors. There can be scary transient impulses on the mains and those class-X capacitors can never have sufficient voltage rating to handle anything that could hit them, so they have to be designed to flash over and to heal as their short-circuit fault clears.

Gas discharge devices will get flashed on those sorts of transients and each flash uses up some of their life expectancy. Eventually their voltage will have crept up to the point where the downstream protection starts to take damage.

Gas discharge devices are common in telephone systems. Nearby lightning can induce surges in the system and viewed as a complex network of transmission lines you can get multiplication of the peak voltage of transients at some places.

The same thing happens with power networks, a lightning strike somewhere can induce a surge, but the amplitude of the induced transient is modified by transmission line effects.

More locally, switched inductive loads can put serious transients of power circuits. In the eighties, we had trouble with some instruments failing at one customer and so I got the job of looking into mains transients on that site. I started looking at our own and found overnight voltage spikes far above expectations. Cleaners were plugging floor polisher machines into engineering benches, and the two horsepower motors were gated on and off by a trigger switch on the handle. At the customer's site there was a large elevator motor with a rather crude starter switch making kilovolt spikes.

Once you dig into these areas, you start to realise that a lot of equipment faults were a case of "It didnae fail, it was pushed"

If you come across a gas discharge device that looks like it's had a hard life, it is best to fit a new one. It is evidence that it's been doing its job and that it is needed.

David

[Drewpicker]

First of all thanks to R, Symon, DA, and David for your help ... I've been looking at this recorder again this evening.. if anyone has the time to help me look for an obvious fault the service manual can be found here
( it's the RDR-DC205)

https://elektrotanya.com/sony_rdr_dc.../download.html

I presume the surge absorber is not to blame ... from what I can see the Power supply is giving all the correct voltages out ... to the DVD the HD and to the board
MB-129 ... the 5.8v and 12v are both present .
When i plug in to the mains the DVD looks for a disk and the HD spins ... I get different voltages of around -21vdc on the top rails of the VF display ... Refugee talked about "a getter" I'm afraid I don't know what that is or how to test the heater for continuity ... or where to find it mostly... Normally the clock stays on when plugged in and turned off ... theres power to the USB port ... there is absolutely nothing in the display at all times and I don't think the infrared to the remote is working ... it does however go into service mode when I hold play and eject down and plug it in .....and that shows up on the tv .. the circuitry in this unit is way above my level but if it's just something simple that needs changing out then that I can probably do ... I'm loathe to let this go to landfill if its something simple although I would recuperate what I could if its condemned.... if anyone has any ideas for this they're more than welcome ... all the best .. Andrew

[dave cox]

You can check an I-R remote with the camera built in to a mobile phone - you can see the pulsing.

The 'getter' is a material in the FV display that helps keeps the vacuum by absorbing / reacting with any gas present. If the vacuum is lost it will react completely, probably turning from a dark/silver to white.

HTH, dc

[Drewpicker]

Having dismantled the vf display I can now see black smearing on the inside (see photo) which looks to maybe emanate from a component inside the vf display (see other photo)... could this be the aforementioned " "heater" or "getter" and be the problem causing the display to not function at all ?

[Drewpicker]

HI Dave thanks for your help with this. I presume you mean regarding the sensor in video mode ... I'll look at that ... I'll have to reassemble it all roughly first.

[Refugee]

It looks like the optical filter has begun to de-laminate.
That will not stop the display working.
The getter will be a dark patch on the inside of the glass away from the electrical connections and viewing area.

[Drewpicker]

Hi R ... these are the dark patches I see on the display... if that's what you meant ... when I was looking yesterday I was getting -21VDC on the 2 outer pins (both sides if I remember right and roughly -25vdc on the inner ones though some to the left had slightly lower voltages... but absolutely nothing lighting on the display at all ... do you think the problem is with the display itself or the circuit controlling it ? ... theres a DC-DC converter underneath the display... I should maybe look at that ... but I have no idea how to find a fault with this ... it's way beyond my limited knowledge.

[Refugee]

There should be a low voltage perhaps AC between the pins with -21 volts on them.
Expect something like 1V on them possibly via a resistor that gets warm.

[Drewpicker]

Ok thanks R ... I'll reassemble it later on tonight and have a closer look at the voltages and report back ...
cheers Andrew.

[Drewpicker]

Sorry for the delay ... had a few problems to deal with today .... ive tested the voltages on the display (in standby mode) ... on both outer pairs of pins each is -20.32vdc .... then from left to right on the middle pins I get -26.1v -21.9v -25.5v then -26.1v on the following 43 pins .... there's no positive or small voltages present.... ...

[Refugee]

The heaters are often 1 volt or something like that.

[Drewpicker]

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 ?

[Drewpicker]

Here's the full schematic for the display board .
hope its clear enough as it's a screenshot.