Batboard

Hello all. I'm new here and have a question which may be simple.
First, a little about me. Retired after 40 years working with Residential/Commercial and Automotive electrical systems and repair.
Generally though, I never had to delve into repair of any power supply. I normally just replaced transformers or the entire supply unit as they were furnished by the parts department.

Brings me to my question. I recently bought a Motorola HPN 1004A at an estate sale. Thought it would make a good power supply for bench testing most regular automotive equipment which requires a "12V" power supply. Label states 120V AC input, 14.2V DC output. Seemed perfect. When I got home and put a meter on it, the output reads 22.9V DC !!

Ant ideas on what may have been changed or why this unit puts out almost double the rated output. More importantly, any ideas on what I can do to fix this and set it back to the rated 14.2V DC output.

Any advice or help will be greatly appreciated.

Thanks.

Everything you need should be here. GARY
http://www.repeater-builder.com/motorola/moto-ps.html

I see on repeater builder that the HPN1004 was the same as the TPN1136

Schematic for the TPN1136 is here: http://www.repeater-builder.com/motorol ... -early.pdf or http://www.repeater-builder.com/motorol ... -later.pdf

I would say with 23 volts out, you have a shorted pass transistor. Those will be the 2 on the back of the unit (Q4 and Q5). Unsolder the connections and do a diode check. I bet one is shorted.

I appreciate the help and am inclined to think you guys are correct. But my problem is that this unit only has 1 transistor or diode on the back. There is a space for another one, but no loose wires. So it may have been modified intentionally. While the TPN1136 may be designed to replace the HPN1007, which was designed to replace the HPN1004, since they have different voltage outputs and appear to be totally different design at least as far as the layout goes, I would assume the internal parts are different also.
Does anyone have a schematic for the HPN1104? Or a parts list? I can included some internal photos of the HPN1004 so you could see the difference, if that would be helpful?

N4KVE wrote:Everything you need should be here. GARY
http://www.repeater-builder.com/motorola/moto-ps.html

Exactly, they are much the same circuit even with one power transistor on the heatsink.

This is what most of them are like: http://www.repeater-builder.com/motorol ... ematic.pdf

C 2 goes bad, the pass transistor Q4 goes open, a common problem.

The schematics posted are for the HPN1007 or the TPN1136, which are both supposed to be replacements for the HPN1004. However, they are both designed on a relatively square chassis and with a different voltage output than the HPN1004, which makes it a little harder for someone like me to figure out. While I have a good understanding of most things electrical, and most of the tools or meters to test things; I have very limited experience in electronics as such. So I'm not sure if someone has modified this by removing some parts and changing the wiring, or if I just may have a defective part as suggested. I'll post photos of the HPN1004 at :
https://picasaweb.google.com/FredWright ... wJnGz_LuPw

It would be a great help if anyone can tell me from these whether the other schematics are close enough to this or if they are different enough to matter. And maybe someone will be able to tell from looking at what I actually have, if it has been modified or not. I'm guessing from the responses that have been posted that if it has not been modified, I need to do a diode or transistor check, but if it has been, I may need to replace a part and wire it back to the original configuration.

Thanks for all for the help so far, I think with just a bit more info I'll be able to get it figured out.

Schematic should be close except for only having one output transistor, and they may have left out the 2nd driver, hard to tell in the pictures.
Odds are you'll just have to replace the large cap on the regulator board (C2) and the output transistor. Cap should be 100uF/25V axial lead. Transistor can be a 2N3772.
You might want to check the zener diode (VR1) as well, it should have around 6.8V across it.

It's not going to be a high power supply, I think that model was meant for the 10-15W radios, but it can be a fun little project.

Old Photo Man,

Yes the schematic I linked to IS for that series. As Jack states one pass transistor and 2N3772 works very well in these.

http://www.repeater-builder.com/motorol ... ematic.pdf

Thanks guys, I'll see what I can do with it.