ATI Paragon PPS1 +20V Power Supply Regulator not working

[nevetslab]

I was given two more ATI Paragon PPS1 Power Supplies that run the beautifully built Live Sound Mix Consoles, from the mid-1980’s thru late 1990’s. One of them I had re-capped before, after repairing the failed 35A 200V Diode Bridge Rectifiers. It had the same diode bridge failure after a couple years of service, so that was an easy fix.

This other turns out to have a faulty +20V Supply Regulator, one that I’ve never serviced. It had a shorted Pass Xstr…TIP35B part, one of six. Now obsolete parts, but I was able to track down 10 pcs each of TIP35C and TIP36C NPN’s and PNP’s, found only one shorted, replaced that. I also found R96 470 ohm 1/4W resistor from the Drive terminal of the Error Amp had burn mark on it, and replaced it with a 470 ohm 1/2W.



With the other five Pass Xstrs unsoldered and completely isolated from the foil pattern, I was able to run it up on the variac/power analyzer, monitoring the output voltage, but found it NOT regulating. Watching the -20V regulator along with this +20V regulator, it’s DRIVE terminal of the Error Amp runs 3 junctions higher than the output buss, then stops at the regulation threshold and the output of it is NOT regulating as I run the AC mains on up. To my surprise, the DRIVE terminal of the +20V regulator drops to 0V at the threshold of Regulation, and NEVER holds the drive circuitry steady. The +20V supply output continues to climb as I turn the Variac up towards 120VAC. -20V supply works fine.





I just checked the new Pass Xstr, and found, after de-soldering it, I had installed a TIP36C PNP….NOT a TIP35C NPN that I thought I had done. So much for my eyesight. I spent a bloody week believing there’s a regulator problem, and after swapping parts with a 3.3V Error amp that had the same dual matched NPN’s and PNP’s, along with replacing the Error amp Q1 & Drive Xstr Q35, swapping out 2N5550 and 2N5401 with MPSA06 & MPSA56 in the Error amp to no avail (and restoring them),

I took photos this morning, and during writing up this thread, I decided to unsolder and replace the new Pass Xstr I replace a week ago. Wrong part! The pitfalls of working alone, and being overly confident in what I had done so carefully, but misreading the small faint silkscreen on the new parts. Now checking it under load.

Everything is working as expected, and as it should have done a week ago! Now, I gotta account for this blunder in my billing! GRRRR!

I also found I had mislabeled the Dual NPN Matched Transistor pair, which should be 2SC3086, NOT 2SC3088. Too bad those two are now obsolete parts!

[nevetslab]

I just heard back from my client that the PPS1 Power Supply that I had only replaced the pair of 35A/200V Bridge Rectifiers (that power the +/- 20V Regulators for the ATI Paragon Console) lasted 5 minutes and popped it's circuit breaker. I don't yet have the power supply back, but am assuming this is again those 35A bridges.

This pair of bridges are wired such that the each (+) terminal and (-) terminal are in parallel, giving the effective rating of 70A, while the AC input to the two bridges are also wired in parallel. I'm now looking into picking up a couple 100A/1KV bridge rectifier module, which is a larger package than these 35A bridges are in. There are eight total bridge rectifiers in this power supply of the same physical size. These 35A/200V bridges are mounted below the 12V and 3.3V 25A/200V bridges. So I don't yet know how much of a PITA this change is going to make.

The load rating on the power supply in the documentation is 20A on both the +20V and -20V supplies. For all I know, it was one of the regulators that failed and not the bridge.

I've always been hesitant with the assumed current rating being doubled when you wire two bridges up that way. More to follow

[Jon Snell]

There are plenty of TIP35 and TIP36s out there and they are still in production. I would choose the C variant for a higher breakdown voltage and the T0247 is easier to mount than the older packets.
https://uk.rs-online.com/web/c/semic..._ALPHA_NUMERIC
The matched pairs can be easily made with two NPN or PNP beta matched transistors, of the exact same type, thermally bonded together. They don't often, if ever, fail.

[Jon Snell]

I just heard back from my client that the PPS1 Power Supply that I had only replaced the pair of 35A/200V Bridge Rectifiers (that power the +/- 20V Regulators for the ATI Paragon Console) lasted 5 minutes and popped it's circuit breaker. I don't yet have the power supply back, but am assuming this is again those 35A bridges.

This pair of bridges are wired such that the each (+) terminal and (-) terminal are in parallel, giving the effective rating of 70A, while the AC input to the two bridges are also wired in parallel. I'm now looking into picking up a couple 100A/1KV bridge rectifier module, which is a larger package than these 35A bridges are in. There are eight total bridge rectifiers in this power supply of the same physical size. These 35A/200V bridges are mounted below the 12V and 3.3V 25A/200V bridges. So I don't yet know how much of a PITA this change is going to make.

The load rating on the power supply in the documentation is 20A on both the +20V and -20V supplies. For all I know, it was one of the regulators that failed and not the bridge.

I've always been hesitant with the assumed current rating being doubled when you wire two bridges up that way. More to follow

If the bridge is connected using spade connectors, that is the weak link due to heat and adding a ridiculously high current bridge may not be the answer. Re crimp the connectors first.

[nevetslab]

There are plenty of TIP35 and TIP36s out there and they are still in production. I would choose the C variant for a higher breakdown voltage and the T0247 is easier to mount than the older packets.
https://uk.rs-online.com/web/c/semic..._ALPHA_NUMERIC
The matched pairs can be easily made with two NPN or PNP beta matched transistors, of the exact same type, thermally bonded together. They don't often, if ever, fail.

That's what I purchased for the repair on that PPS1 that had failure in the pass xstrs of it's +20V regulator.

[nevetslab]

I received the PPS1 Console power supply this morning, and got it onto the bench a little while ago. The wiring configuration of the two bridges is very odd, not like I would have expected. When I first saw it back in July 2021, I thought I was seeing a wiring mistake, but that's how it IS wired.

Today, with the two bridges removed, having found one with a short between one of the AC inputs and the (+) terminal, I then powered it up, with the bipolar 20V supply, +12V and +3.3V bridges removed, then measured what the unregulated AC voltage is that's feeding the two bridge rectifiers.



ATI PARAGON PPS1 BIPOLAR UNREG PS-2.pdf

It measured 75.6VAC unloaded. The Unregulated buss caps in this supply are 10,000uF/50V. So, thinking of wiring the two bridges in a conventional style would be over +50VDC, when the unregulated supply is called out as +/- 27VDC. So, they ARE using this configuration in half-wave rectification, with the two bridges DC outputs in parallel, and each bridge is fed by one of the two secondary taps, and the potential is between each tap and CT ground. The Output from the Bridges couple to the 10,000uF Filter caps thru huge inductors, DCR measured 0.10 ohms. I didn't take the time to measure the inductance. Very odd. Until I drew this circuit up, I was starting to think of using a 100A Bridge Rectifier, but that would be feeding that higher secondary winding to the AC inputs, and put the input caps over-voltage, as well as running the pass xstrs at much higher voltage.



I replaced the shorted bridge, along with the other, just to be safe. It powers up again ok. I didn't receive my power supply load interface box with this supply, so I'll have to wait until tomorrow to get that.

[nevetslab]

If the bridge is connected using spade connectors, that is the weak link due to heat and adding a ridiculously high current bridge may not be the answer. Re crimp the connectors first.

I did just find two of the bridge push-on Spade Lugs showing overheating signs, both the added (+) & (-) terminals to the second bridge (where both on each bridge outputs are in parallel). All others look fine on the two bridges. I replaced the terminals, and verified all of the connections are good and tight.

Correction: the bridge configuration IS full wave Bridge, and NOT Half-Wave as previously stated. Just looks odd as they have it wired. I haven't yet gathered the range of unregulated voltages under different output current loads of the +/- 20V supplies. I'm waiting for the power supply load adapter cable from my client so I can do that.

[nevetslab]

My client brought back the adapter cable/load connection box so I could check this under load.

Under no load, the +/- 20V Regulator input voltage was +/- 50VDC. Loaded the outputs with 2 ohm loads for 10ADC, the unreg supply was +/-30.5VDC, with AC Mains readings of 6.8A/2.1kW @ 120VAC. With 1 ohm loads for 20ADC, the unreg supply was +/- 28.7VDC, with AC Mains readings of 12.9A/4.06KW @ 120VAC. I then set the load to 1.33 ohms for 15ADC, with the unreg supply being +/- 29.8VDC, and AC Mains readings of 9.9A/3.1kW @ 120VAC. I let it run at this level for 4 hrs.

The client had changed the higher speed fan to a pair of slower fans (one on the front panel, other inside), which was done to lower the acoustic noise of the supply. That at the expense of increasing the temperature of the pass xstrs. I saw a range of temps from the front row of fins at around 60deg C, and the rear row of fins at the pass xstrs sitting around 100 deg C! That makes me nervous, and I'll have a chat with the client on that. I was using an IR probe for those readings. With the IR probe, I looked around at the pair of bridge rectifiers for the +/- 20V supplies, only seeing the bridges around 50 deg C, while seeing temps around 65 deg C on the push-on insulated lugs of the load and source cables.

At least this ran for longer than the 5 minutes that I heard about, which brought it back to me for repair.

[g1]

Correction: the bridge configuration IS full wave Bridge, and NOT Half-Wave as previously stated. Just looks odd as they have it wired.

From what I can see, if you draw up a standard split supply bridge circuit, and put 2 parallel diodes in each leg, that is what you would have.

[nevetslab]

I was puzzled by the wattage readings of my Magtrol 4614B Power Analyzer. It's a 3-phase 100A instrument, and can measure power factor, time-averaging of the load/voltage readings. I have the three phases strapped so I can get Power Factor readings on single phase. The button that selects single or three phase on the Power Meter was set for 3 phase, so the readings were abnormally high, being multiplied by 3. Opps!

The correct readings made today were:

2 ohm loads
+/- 20.0VDC @ 10A ea
6.83A/704W @ 120VAC

1 ohm loads
+/- 19.8VDC @ 20A ea
12.8A/1353W @ 120VAC

1.33 ohm loads
+/- 19.9VDC @ 15A ea
9.7A/1025W @ 120VAC

[a1fohengineer`]

NeveTsLab can you reach out to me please a1fohengineer@gmail.com having some issues with a ATI Paragon a few people said you are the guy LOL

[g1]

nevetslab , see post #11 above.