(Topic ID: 182151)

Gottlieb System 80 - No displays, low 60V and 42V

By solarvalue

7 years ago


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CR5 (resized).jpg
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#5 7 years ago

Could be any of several issues... all centered around Q1.

First step - check HV coming into the board.
With connector pulled from J3 -- what do you measure between E1 and ground? And what do you measure between E2 and ground?

#7 7 years ago

OK -- power in ok although a bit high.
Low E2. Can be bad CR5 or Q2 circuit or shorted output.
Next, to check for shorted output -- black meter lead to TP3, what is voltage on both sides of R4 (33 ohm resistor).

#9 7 years ago

OK -- not shorted output.

Low voltage on E2 during normal operation means the output is shorted and the regulator has gone into current limiting mode. But that's not your problem.

In your case:
Bad Q1, Bad CR5 or Bad Q2. If you have a meter with diode test - start checking those three.
All three of these are fairly cheap. Q1 = TIP31C, Q2 = 2N5550 or 2N5551, CR5 = 1N4759A. The bad thing about fixing this power supply board is removing that stupid hotplate heat sink... which can bugger up your +5V supply.

Also take a quick look at resistors R1, R2 and R3. R1 cracked?
Based on the 13V output - if R2 and R3 are ok then you should be seeing about 1 volt across resistor R2 and 12 volts across resistor R3.

Ed

#12 7 years ago

Pretty much ... yep.

OK...

and Yep.

But - if you are disconnecting things, may as well just replace the set of three (zener diode and two transistors). They're dirt cheap - your time required for testing these three parts is worth more than the value of the parts. The only bad thing about replacing these three is pulling the 5V regulator transistor off and re-attaching when done.

2 weeks later
#14 7 years ago

Not necessarily a bad R2. "About 13V" at left of R4 plus resistor tolerances - they appear to be fine. So this does show the voltage divider (R2 and R3) is pretty close so that ain't the problem.

CR5 voltage should be 62 but you mentioned 13V above. And your output voltage is hovering 13V so is following the CR5 input voltage (CR5 tells transistor what voltage he should be outputting). First thing I'd change out is CR5. CR5 is mounted to standoffs - a definite plus because you can replace him without dismantling the board from heatsink.

Original CR5 was rated at 62V with max power dissipation of 1 Watt. With R1 = 1.3K and your input to R1 (measured at E1) at a high 98-100V --> current through R1 = about 29mA (plus a hair for Q1). This means CR5 is also conducting at nearly 29mA. CR5 power = 62V x 0.029A = 1.8 Watts. Yup, that's about 2x maximum of what he should be doing. This is partially a result to running your input voltage so high. And partially a result to Gottlieb using an undersized part. Replace him with a 5 watt part: 1N5372B.

#16 7 years ago

Oh - that's unfortunate. They didn't use standoffs for your CR5. You could do as you say cut him off and solder to leads on top of board. This would save yourself some work and headache regarding not pulling the TO-3 big transistor off the board.
Normally I would consider that a kluge but this board is so stinking tough to work with - I would go that route and maintain your +5V regulator circuit's integrity. Here is what my CR5 looks like...

CR5 (resized).jpgCR5 (resized).jpg

#19 7 years ago

Nah, you're at the upper edge of the 10% tolerance but you're fine.

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