Pentranic #1432 chassis chirping

[kyle1111]

Hi, I'm hoping somebody out there will be able to give me some advice on what else I can try to get this Pentranic CGA/EGA chassis to work. 

First of all the chassis will start chirping as soon as you turn it on and there is no picture.  I have checked all capacitors on the board and replaced any that had high ESR's.  The result was still the same, so I replaced the k1507 MOSFET and the control IC TDA4605-03 as I believe the problem is in the switching power supply.  It's still chirping so I changed out the BU2520 HOT with no change.  When I measure the B+ voltage on the D501 diode it only measures 20 VDC.  Adjusting the VR501 trimpot only varies this between 18V and 21V, which is far away from the 118V it is supposed to be.

Since then I purchased an AS-IS untested chassis on Ebay, hoping it would work, or I would be able to make 1 work out of the 2 of them.  With my luck it turned out the AS-IS chassis chirps just as well as the original chassis.

I'm hoping somebody will be able to give me an idea of what I could try next or maybe have access to a service manual for this chassis.  This arcade machine is sort of my hobby, and I am very new to monitor repair, basically whatever I've read on the internet.  Thanks in advance!

[qrz]

check ALL the supply outputs for high loads (shorts).
vert output ic's do short on occasion . in some tv circuitry, it is sourced from the smps rather than the flyback.
in those chassis, the extra load is sufficient to effect a high current shutdown of the smps .
it may be sourced similarly in the Pentranic ?

qrz

[Arm123]

Hey Kyle, i have a thread open here with which sounds like the same issue.

http://forum.arcadecontrols.com/index.php?topic=67429.0

I also changed TDA4605-03 and BU2520 with no change.  I tested the k1507 MOSFET and it checked out as good.  I would have replaced it, but i couldn’t source any around here (hard to find).

I have put this aside, but since you are working on one as well, I will pick up again.

I am interested in seeing what happens.

[Rickn]

The Chirping is normally the HOT, but you have replaced that....

Try pulling the HOT and connecting a 60 watt light bulb in series, from the collector to ground.

If the light bulb lights and you read somewhere between 113 and 130 VDC at cathode D501 ( the B+ varies depending on the tube) then the problem is not likely in the supply.

Let me know how you make out with this and I will try to help you more.

Good Luck

Rick Nieman
www.Niemandisplays.com
Rick@Niemandisplays.com

[kyle1111]

I just removed the HOT and connected the 60W light bulb from collector to ground.  The light bulb did not light up, and I am reading zero on the B+.  Does this mean it is the supply?

I've just been called to work out of town, so I won't be able to get back to this for about a week.  So any ideas you guys come up with in the meantime are greatly appreciated. 

Thanks again for the help!

[Rickn]

Yes, although it is not 100%- definitely leads to the power supply.

Next step, measure the dc voltage across the bridge rectifier's output- I am pretty sure you will have about 165 volts, but need to confirm.

If so everything before the bridge is fine.

Let us know and then next we will work on 3 components:
- Start-up resistor
- Start-up Capacitor
- Switching transistor/fet.

Rick Nieman

WWW.Niemandisplays.com

[qrz]

switch mode power supplies can, at times,  be a challenge to repair .
a schematic can be the difference . 
seems to be proprietory info . so, may have to sign away your first born , but can make a request here :
www.pentranic.co.uk/spare-parts-schematics.htm.
did find a bit about a buyout by wells-gardner. so the above may change...some day  ??
again , check for shorts on every diode on the main xformer . on the hot side , check ALL resistors and
 semiconductors .
when the supply was chirping , it was functioning. that is attempting to output voltage .
it now sounds DOA   

qrz

[Rickn]

Schematic, no problem.

Just e-mail me and I will send it in PDF.

Rick@niemandisplays.com

[kyle1111]

Across the bridge rectifier I do have 165 Volts.  I also have a schematic but does not give me any voltages or test points, so It makes it difficult for a newbie to troubleshoot.  I will check again for shorts.  One chassis still chirps, the other does not.  I am working on the one that still chirps.

[Rickn]

So Ok you have narrowed it down to the power supply, (the light bulb did not light and no B+). You have ruled out everythinhg before the bridge, (as you have 165 across the bridge.

Check for a shorted regulator Fet Q501, an open start-up resistor R510. C516 start up cap as well as C551 and c313.

In fact if the fet is ok go for R510 and C313 first.

Good Luck

Rick Nieman
www.Niemandisplays.com