Batboard

Can anyone point me to a schematic for the TPN1154A power supply? I have one here that puts out 15V+ with no load, and drops to 1V with a small load. Unregulated side looks good at 22V+ steady. I pulled the pass transistors (one is shorted, will replace pair) but the problem still exists even with the bad pass transistor removed. The regulation section is zener based, no LM723... thinking of just replacing with a 723! No crowbar either...

Thanks!

Steve
KV6O

Now you have me confused. If one of the pass transistors was shorted, it would either give you the
full voltage all the time or nothing all the time. It wouldn't change much with load. I would start by
replacing both of the pass transistors.

Your next problem is trying to fix the voltage regulator. If my memory still can recall those power
supplies, there was a chase your a$$$ around regulation circuit in those power supplies. You
could spend a good deal of time going in circles and still not locate the problem. Your efforts would
be better spent once you obtain a diagram of the beast. Then try looking for the problem.

Jim

kv6o wrote:Can anyone point me to a schematic for the TPN1154A power supply? I have one here that puts out 15V+ with no load, and drops to 1V with a small load. Unregulated side looks good at 22V+ steady. I pulled the pass transistors (one is shorted, will replace pair) but the problem still exists even with the bad pass transistor removed. The regulation section is zener based, no LM723... thinking of just replacing with a 723! No crowbar either...

Thanks!

Steve
KV6O

I know, the symptoms didn't make sense... I will replace both with 2N3771's, but am on the fence on if I should just replace the regulator with a 723. I think I'll sit down and draw out the schematic - looks like a 6.8 or so zener (I measured it, don't remember right now) with a feedback driving a transistor. The last test I did was with the one pass transistor in circuit, I'll take it out and look at the output from the PNP driver (it tested good).

The symptoms (besides the shorted pass transistor) seemed to indicate that the feedback portion it messed up, the error it driving it down to 1V... I guess I'll take a stab at it for fun!

A schematic would sure be nice!

Steve
KV6O

I've got a schematic for those, will have to scan it in and send it when I get a chance later.

jackhackett wrote:I've got a schematic for those, will have to scan it in and send it when I get a chance later.

Jack,

Can I get a copy. I did not have that one in my books.

Sure, have it in PDF format I can email, alternatively I could put it up as images on my photobucket, let me know which way works better for you.

as for those symptoms.. from the looks of it there's a 470 ohm resistor that parallels the outputs, so if they were taken out it might still regulate, but wouldn't handle any current. I'd check the 0.1 ohm 7W resistors to see if they're open.


btw... you might check some older mobile radio service manuals under the auxiliary equipment section, I found it in a a Motrar book.

PM sent! Thanks!

Steve
KV6O

one other thing... you might want to check the two electrolytic caps while you're at it, those supplies are generally old enough for the caps to start drying out.

Well, the 2 0.1Ohm ballast resisters both read over 2K - so that's why my shorted pass transistor didn't put 22+V out, and why under a slight load the voltage dropped to 1V or so... Still waiting for my new pass transistors (2n3771's) but with a new 0.1Ohm 25W resistor and the remaining good pass transistor I was able to put a few amps load on it and regulation held. The output voltage is a bit high (15.1V) so I'll take a look at that and once I can put a good load on it I'll have a look at the ripple to see if the cap is any good.

Thanks for your help!

Steve
KV6O

Now I remember those.. I always had to replace C2 and add R9 to get the voltage down to 13.5 volts.

Schematic diagrams in PDF for the Motorola TPN1136A, TPN1154A, and VPN1013A power supplies are now posted in the Power Supplies folder in the Repeater-Builder Group Files section. As others have noted, all three power supplies are very similar, but the latter two have dual-voltage transformers and a 25,000 uF filter capacitor. The TPN1136A has a 120 VAC-only transformer and an 11,000 uF filter capacitor. Curiously, I own a stock TPN1136A power supply that has two M9244 pass transistors in parallel, even though the schematic diagram for it shows a single M9639 pass transistor.

I ran a load test on my TPN1136A power supply, and found that it can carry over 17 amperes- if the AC Mains fuse is increased in rating. With the specified 2A fuse in place, the supply can carry about 7.5 amperes. The load test report is found in the above-mentioned folder.

For those readers who want to vary the output voltage of a TPN1136A or TPN1154A power supply, note that the VPN1013A power supply schematic shows a 500-ohm pot that was added to vary the base bias on Reference Amplifier Q2.

73, Eric Lemmon WB6FLY