PG506 in need of parts T130


Timothy
 

I bought a parts PG506 years ago and I mostly took cosmetic parts from it. I was bored so I plugged it in and its completely dead, no voltage at the test points to speak of. After checking some components in the power area I believe the transformer T130 has a short. Is there a known replacement part available or will I need another donor if I want to keep playing with this?

Also I need precision resistor R300 if anyone can help with any of this I appreciate it!


Zentronics42@...
 

Timothy,
You might have a quite a bit of trouble replacing T130, I have to ask the question how was this confirmed bad? The PG506 has a switching power supply built in to the unit. It was needed to boost the frame voltage up to 100Vdc for the plugin. The good news is unless the transformer was abused it SHOULD be ok. Usually something else dies in the switchers. Cap, switching transistor, switching transistor controller. Or possibly the kick start circuit. Transformers tend to be pretty simple... until they arnt. And unless the insulation fails or they are over loaded they tend to stick around. The precision R300 will be an easy replace. It will just be a matter of finding a equal or better replacement from one of the parts houses, Digikey, Mouser, Element 14. With modern construction the precision should be easy to meet or exceed.

Zen

-----Original Message-----
From: TekScopes@groups.io <TekScopes@groups.io> On Behalf Of Timothy via groups.io
Sent: Friday, September 10, 2021 1:20 AM
To: TekScopes@groups.io
Subject: [TekScopes] PG506 in need of parts T130

I bought a parts PG506 years ago and I mostly took cosmetic parts from it. I was bored so I plugged it in and its completely dead, no voltage at the test points to speak of. After checking some components in the power area I believe the transformer T130 has a short. Is there a known replacement part available or will I need another donor if I want to keep playing with this?

Also I need precision resistor R300 if anyone can help with any of this I appreciate it!


Timothy
 

I measured 5M ohm resistance between the windings and I understand you cant trust that with the part in circuit so I did unsolder the leads however I left it in place when I retested. After reading your reply I decided to double check my work and I should have pulled the part free from the board. I have seen people test parts in place after desoldering on youtube, but my hand must be too heavy and I complete the circuit. I pulled it free and its a dead short now, I think it is ok. However on the board there is now 1M ohm resistance between say the pin locations 1 and 10.


Zentronics42@...
 

Hmm ok something is odd. Transformers should show almost a dead short at DC when you are looking at the windings end to end. However on the different set of windings there should be no connection at DC. Which is what the meter is using. Next thing to look for is a pin out of the transformer or the schematic of the power supply that should tell you what pins are connected and what pins are not connected. In circuit measurements can be influenced by the active components in the circuit. A meter can have enough voltage to forward a transistor or diode and part way turn them on. This will throw off measurements and cause readings to be at best weird. At worst fry a sensitive component. For instance a DMM can kill a tunnel diode. Also check the board. I had an issue in the power supply of one of my TM5006 units. The through hole on the circuit board went bad. Had voltage on the top of the board but not the bottom. Very odd fault and definitely not common. Probing around the transformer with the unit powered up should be done with care there is high frequency high voltage AC at that location. And the PG506 specifically has some elevated voltages in it.

Zen

-----Original Message-----
From: TekScopes@groups.io <TekScopes@groups.io> On Behalf Of Timothy via groups.io
Sent: Saturday, September 11, 2021 1:41 PM
To: TekScopes@groups.io
Subject: Re: [TekScopes] PG506 in need of parts T130

I measured 5M ohm resistance between the windings and I understand you cant trust that with the part in circuit so I did unsolder the leads however I left it in place when I retested. After reading your reply I decided to double check my work and I should have pulled the part free from the board. I have seen people test parts in place after desoldering on youtube, but my hand must be too heavy and I complete the circuit. I pulled it free and its a dead short now, I think it is ok. However on the board there is now 1M ohm resistance between say the pin locations 1 and 10.


Timothy
 

I checked the board and it was kind of dirty near the back that is uncovered. Cleaning this did bring the resistance between the points I was testing up but you were right, I was going in the wrong direction. I went back to basics. I had already checked all caps. I replaced some tantalums that were suspect. Double check work... There culprit was a bad electrolytic cap C150 or C145, I replaced both.

There are secondary problems but I now have lights, WOW so cool! Next I will check voltages, I am going to clean and reseat all the ICs, check all of the tantalums then see whats working and whats not.