Phonoland

Ok, So I decided to replace all the caps in my amp from my STD3 (its an SHP3 amp) I used the parts guide posted on Tony's Arcade site. I compared the values to the caps as I removed to make sure everything was cool. I replaced the caps, and met resistors as well as the driver transistors on the driver board, the caps on the pre-amp board, the caps on the inner chassis and the caps and transistors on the outer chassis. When I plugged the unit in a small stream of smoke appeared from the outer chassis transistor heat sink. I pulled the heat sink off and found that the smoke was coming from a resistor on the back side. I have posted a picture. I also found a couple of odd items that did not look normal. First on the driver board, there is a ceramic cap soldered with the #3(from left) transistor, but the actual numbered location is empty with factory solder covering the holes. Second, there is a fuse soldered between two terminal strips. The fuse body is empty, but had a fuse holder attached to it with a blown fuse in it. The unit functioned before I rebuilt the amp. My best guess on the fuse is that it is for the paging amp, whatever that is. I am hoping someone can shed some light on where I went wrong (if I did) and how I can figure out the problem. Sorry for the long post, just alot of information.

Sorry to say-but, If you had purchased Tony's SHP amp book, you would have had most of the answers to your questions.
First two are normal (2A fuse is for PRVC/mic only --as shown in schematics)--last one, if its the cement block resistor (can't tell from pix), or anything that looks "burnt" --it's probably failed, along with maybe a transistor++++??
Can't fathom a guess as to what you did wrong without seeing the amp, but if it was working prior, I would have to assume that something you have done was incorrect--then only maybe--could have been just "time" ?? Ron Rich

Ron,

I am planning on buying Tony's book, but did not have the cash at the time, It's next on the list. As to the wiring, I replaced all components according to polarity. The only question in my mind were the two large 3000uf caps on the outer chassis. I am pretty sure I got that right. The resistor that is smoking is the 30ohm resistor in the picture (I put an arrow next to it) The transistors are all brand new. I guess I could replace the 30ohm resistor and see where that gets me. I also get a hum out of the speakers when it is powered on, and the smoke does not appear right away, takes a minute. Thanks for any help that you can provide.

Ordered Tony's amp book, as well as the black and grey book. I am going to replace the 30 ohm resistor. What wattage resistor should I buy?

I am not a jukebox tech, so excuse me if there is a logical answer, but why would you replace transistors on a functioning amp?

I have seen similar components fail on newer equipment. The constant heating / cooling cycle over a period of years can take it's toll for sure. The cost of the transistors in not much, so why not replace them with newer technology and manufacturing conditions? I suppose it was not really required, but since I had it all apart, might as well.

I see no logic to replacing solid state components, for "newer" ones. Failure rate for "new" stuff is high for the first 30 days. I have seen brand new components fail seconds after the initial "power up". Ron Rich

Ok, we all have our opinions on the components, but back to the issue at hand. I think I have narrowed down the issue to the 4 transistor on the outer chassis. When I replaced them there were two that were originally installed flipped with the writing upside down. I installed the new ones the same way. Perhaps that was my mistake. So I then re-installed the old ones in what I thought to be the right configuration, but got more smoke than before (both sides and faster.) Can someone post a picture of the 4 transistors on the SHP3 amp outer chassis so I can see the correct configuration? The picture at the tony's arcade site shows the transistors all installed with the writing up, but that is a SHP1 and am not sure if they are the same in that regard. I have ordered Tony's book, but that won't be here for a couple of days and am not sure that it will have the info I need.

The "writing" on the transistors makes no difference--just depends on brand and run date. Transistors will only mount one way, as the pins are "off center".
Ron Rich

Ok, then that is my problem. I will correct the issue and report. Hopefully I have not done too much damage already.

I put the transistors in the correct placement, however, the insulators behind the heatsink have started to deteriorate and fall apart. Just to test the amp, I hooked it up and got a small stream of smoke out of the right side instead of the left side. Similar to my initial problem. I am starting to get frustrated, What could possibly be the issue. Like I said earlier, I believe that the two transistors on the right were mounted flipped, but not sure. Where can I get the insulators for the back side of the heat sink?

If those transistors were mounted incorrectly, chances are they were destroyed immediately when you powered it up the first time.

hmmm.....I was thinking that as well. I guess they are cheap enough to order some more. Any idea on where to source the black insulators on the bottom side of the heat sink?

Ok, so I ordered new power transistors and got them installed. No smoke, but now, no sound. Where should I start looking? The mech scans and picks up a record and seems to work normally. I can here the mute/trip relay click, and the driver transistors get warm.(well 3 are warm and 1(the left one in the picture in my first post) is very warm). I did have the mech out for some cleaning and lubrication. I have checked the connections and all seems well. Where should I start looking? Any thoughts on what it could be?