GE 9-7500 (Panasonic PV-2700) Power supply problem


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GE 9-7500 (Panasonic PV-2700) Power supply problem

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t0nito
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Jun 26, 2014, 12:32 PM

Post #1 of 16 (6020 views)
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GE 9-7500 (Panasonic PV-2700) Power supply problem	Can't Post

Hi guys.

I have this 1987 GE 9-7500 which is the same as a Panasonic PV-2700, the problem is while I was testing voltages with my DVM because there was no supply to the VFD filament, clumsy me shorted something and now the supply is dead.

Power supply is a VEPS0167

Now when I plug the cord I hear a single tick from the SMPS and then nothing.

If anyone could help or provide a schematic for the power supply I'd be most grateful. It's been in our family for many years and I'd hate to trash it.

jts1957
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Jun 26, 2014, 4:44 PM

Post #2 of 16 (6013 views)
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Re: [t0nito] GE 9-7500 (Panasonic PV-2700) Power supply problem [In reply to]	Can't Post

Check all the semiconductors.
Once back to original symptom (No/Dim Display), changing out all the lytics couldn't hurt.

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Location: Far, Far Away

t0nito
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Jun 26, 2014, 5:34 PM

Post #3 of 16 (6010 views)
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Re: [jts1957] GE 9-7500 (Panasonic PV-2700) Power supply problem [In reply to]	Can't Post

Thank you for your reply.

I'm starting by testing diodes in circuit but there are at least two that are behaving odd, but they're good off circuit.

While in circuit when I test the diode one way it's beeps for continuity like it's shorted than resistance starts rising until 412 Ohm then I reverse the meter leads and it's shorted again than rises to infinity.

Can that mean anything?

Also switching transistor seems ok acording to my transistor L/C ESR tester.

jts1957
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Jun 26, 2014, 5:52 PM

Post #4 of 16 (6009 views)
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Re: [t0nito] GE 9-7500 (Panasonic PV-2700) Power supply problem [In reply to]	Can't Post

As long as they check OK out of circuit, they are fine. Same goes for transistor. (Be sure - 'seems ok' may not be good enough.) Other parts, especially electroLYTIC capacitors will affect meter readings in circuit.

What/Where were you attempting to measure when you slipped?

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Location: Far, Far Away

t0nito
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Jun 26, 2014, 6:25 PM

Post #5 of 16 (6006 views)
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Re: [jts1957] GE 9-7500 (Panasonic PV-2700) Power supply problem [In reply to]	Can't Post

Output voltage to filament.

Ok I have some news. I found on another forum the pinout voltages for the supply they are as follows:

Pin 1 AC 4V
Pin 2 AC 4V
Pin 3 UNSW +5V
Pin 4 UNSW +5V
Pin 5 UNSW -33V
Pin 6 GND
Pin 7 UNSW +14V
Pin 8 UNSW +48V
Pin 9 POWER STOP (L)

Here's what I got (no load)

1-9.8 V AC
2-9.8 V AC
3-0 V
4-0 V
5- -21 V
6-GND
7- 18.5 V
8 - 48 V
9 - 5.1 V
Pin 3 and 4 are tied together, folowing the trace I found a component that I think is a fuse, before that component I get 5.12 V after I get 0V measuring the component there is no continuity.

It's a small black 2 pin component, labeled F 38K.

The cicuit board's reference to this component is "PR1" this is what's puzzling me because fuses are normally "F".

Can you confirm it's a fuse?

t0nito
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Jun 26, 2014, 7:29 PM

Post #6 of 16 (6002 views)
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Re: [t0nito] GE 9-7500 (Panasonic PV-2700) Power supply problem [In reply to]	Can't Post

Good news vcr working again. VFD is still dead though.

So I'm back to my initial issue.

The AC voltage I gave earlier was probably a false reading.

Anyway, if i jump a wire from one of the filament pins to ground the display lights up but though a bit dim, any ideas? All electrolitics from power supply read ok on my esr meter.

EDIT: So my crazy DVM is reading

Between filament pins when in standby: 0.06VAC

2.65VAC spike when turning on (display is a bit brighter during half a second.

0.27VAC when turned on. Makes more sense now.

I'm thinking of recapping the whole secondary side but I think it's something else, here's why:

When I was young and stupid (about 20 years ago I opened the vcr by curiosity, then on top of the VFD there was a 13 pin SIF resistor and I decided it was fun to see "random" stuff on the screen until it sparked and never worked again, now I decidedto fix the damn thing so many years later.

I followed the traces from the filaments and they go directly to the power supply with no components in between.

(This post was edited by t0nito on Jun 26, 2014, 7:56 PM)

jts1957
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Jun 26, 2014, 8:02 PM

Post #7 of 16 (5999 views)
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Re: [t0nito] GE 9-7500 (Panasonic PV-2700) Power supply problem [In reply to]	Can't Post

F38 is IC Protector 1.5A.

http://www.datasheetarchive.com/ICP-F38-datasheet.html

Grab a one and a ten ohm resistor and let me know if they read ok with your ESR (that's correct ESR) meter.

ANY low resistance across a lytic can 'fool' your meter.

EDIT;
If you want to live dangerously ... the filament needs three volts. If you were to "Isolate" the filament pins and apply your own 3 volts (AC or DC) ...

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Location: Far, Far Away

(This post was edited by jts1957 on Jun 26, 2014, 8:12 PM)

t0nito
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Jun 26, 2014, 9:06 PM

Post #8 of 16 (5994 views)
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Re: [jts1957] GE 9-7500 (Panasonic PV-2700) Power supply problem [In reply to]	Can't Post

I was actually thinking about taking that direction, the pinout says 4 VAC should it work with 4 VDC?

I have a variable voltage regulator, should there be a problem if I feed it from the 5 VDC and step it down to 4VDC?

jts1957
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Jun 26, 2014, 9:35 PM

Post #9 of 16 (5991 views)
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Re: [t0nito] GE 9-7500 (Panasonic PV-2700) Power supply problem [In reply to]	Can't Post

Filaments don't care if they're supplied with AC or DC. Most important that you do NOT apply more than double the display's rated value. And then it's usually good to take small steps.

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Location: Far, Far Away

t0nito
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Jun 26, 2014, 9:46 PM

Post #10 of 16 (5989 views)
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Re: [jts1957] GE 9-7500 (Panasonic PV-2700) Power supply problem [In reply to]	Can't Post

Thanks, I'll give it a go!

t0nito
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Jun 27, 2014, 8:23 PM

Post #11 of 16 (5981 views)
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Re: [jts1957] GE 9-7500 (Panasonic PV-2700) Power supply problem [In reply to]	Can't Post

Looks like the VFD is the culprit all along, I guess it's shorted, tester shows continuity between pin which I guess it's normal because it a filament, but I've isolated the pins and used an external power source, I've tried the 5V source with a resistor, no load was 4V when conected to the filament it dropped to 2.3V and the displa was off, used a 9V battery with a linear regulator set to 4V and when connected to the display it dropped almost to zero, I started to raise the voltage on the regulator and it was near zero all the time even after setting it to max, display was off all the time.

Funny thing is that if I connect one of the filaments to the original source and the other pin to ground it will actually work but very dim, like half normal brightnress or less. I don't know if I could leave it connected like this or if it will strain the SMPS. A dim display is better than no display, but a working VCR is better than a dead one, what are your thoughts on this?

jts1957
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Jun 27, 2014, 8:53 PM

Post #12 of 16 (5980 views)
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Re: [t0nito] GE 9-7500 (Panasonic PV-2700) Power supply problem [In reply to]	Can't Post

A little light (pun intended) reading:

http://www.noritake-elec.com/vfd_operation.html

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Location: Far, Far Away

t0nito
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Jul 2, 2014, 8:44 PM

Post #13 of 16 (5953 views)
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Re: [jts1957] GE 9-7500 (Panasonic PV-2700) Power supply problem [In reply to]	Can't Post

Well, that reading just confused me more.

Going back to the vcr, I figured out that the AC voltage is low right at the output of the transformer itself, 0.05VAC in stand-by mode and 0.2VAC when on, even though the voltages are low that difference must be because the display is dimmer when the unit is off, for the life of me I can't figure out what the hell I shorted when I was a stupid child.

Since I couldn't figure out how to fix it with an external supply, I connected one of the filament pins to ground. The result was a dim but working display but with some elements lighting up that weren't supposed to but dimmer, so the display was readeable and I was happy with that, but when I played a tape I noticed a rainbow pattern at the bottom of the screen, so I disconnected that pin to ground connection and the picture is okay again. I guess this VCR is condemned to never have a proper display again...

(This post was edited by t0nito on Jul 2, 2014, 8:45 PM)

t0nito
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Jul 7, 2014, 8:37 PM

Post #14 of 16 (5930 views)
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Re: [jts1957] GE 9-7500 (Panasonic PV-2700) Power supply problem [In reply to]	Can't Post

Hi

Since I'm quite stubborn, I haven't given up just yet, it seem I found the cuprit, I think I was searching in the wrong place.

So I traced the -30V line from the power supply to the VFD board and I found that there is a single resistor on its path. I measure -30V before the resistor and around -2 after the resistor. I took it out and my tester says it's open.

Since unfortunately nature decided to make me colourblind (not joking) I'm having a hard time figuring the value of this resistor, can you help me out?

Thanks

EDIT: So I temporarily threw in a 2K resistor just to give it a quick test, and sure enough the display came back to life 20 years later! But I'd like to put in the stock value (fuse?) resistor...

(This post was edited by t0nito on Jul 7, 2014, 9:17 PM)

jts1957
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Jul 8, 2014, 12:04 AM

Post #15 of 16 (5917 views)
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Re: [t0nito] GE 9-7500 (Panasonic PV-2700) Power supply problem [In reply to]	Can't Post

OR 92,100 ohms 1% tolerance. (Assuming I see from top down: brown-red-brown-red-white)

http://www.electronics2000.co.uk/...-code-calculator.php

Select '5 band code'
Put 92.1 in 'resistance'
Select kohms from ohms drop-down box
Select 1% from drop-down tolerance box

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Location: Far, Far Away

(This post was edited by jts1957 on Jul 8, 2014, 12:06 AM)

t0nito
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Jul 8, 2014, 12:43 PM

Post #16 of 16 (5912 views)
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Re: [jts1957] GE 9-7500 (Panasonic PV-2700) Power supply problem [In reply to]	Can't Post

Thanks for your help, looks brand new!

(This post was edited by t0nito on Jul 8, 2014, 8:32 PM)

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