@ovi4 Sorry I did not see the drop down box that says open share. I changed the view and approved you and all others.
@john-barron the drawings access is now clear. What Larry and myself and others use in here for sharing pictures is a free version of picture sharing service called IMGUR. You just need to register with an account (Job done). The advantage of IMGUR is that you can post a direct link that is embeded meaning the pictures would be visible directly in your post so there is no need to post a link that gets you redirected. However there are many types of links you can choose from one of which being just a normal link that would get viewers redirected to IMGUR site in oder to see your posted pictures . (the choice is your.)
Now onto the main problem. First lets clarify on thing: You say that Q1 and Q3 are PNP’s but if you look closely at the transistors symbols you’ll soon realise that only Q1 is NPN and only Q3 is actually PNP. So both together would be classed as a complementary pair. So, again, if you (visually) follow pins 14 and 29 backwards on the schematic diagram (from the amp toward the power supply) they actually meet at some point to a so called “NODE” So in other words there is (or shouldn’t be) any pottential difference between the two because they should (according to the drawing) be fed of of the same +48v. Now the second problem is that you claim to get -48V instead of +48v on those wires. Well I would say that’s kind of….impossible (according to the drawing).
A couple of notes: all voltages are to be measured with respect of the chassis ground whitch is @ 0V potentiall meaning your ground stands midway (is the middle point) between the =48V potential and the -48V potential as the power supply has a dual rail topology. So you need to get the facts straight by making sure your black Multimeter probe is conneted to 0v (GND) potential when taking the measurements. Beacause if you somehow have the probes in reverse youll be reading (on the digital display of your multimeter) a value of MINUS 48V instead. I hope to be of help.
PS: the only way you get -48V instead of +48V on thoose wires if you.yourself changed some wires or replaced (say) the electrolitics and somehow (by mistake) you’ve re-wired some things (within the power supply) in reverse. So, beware.
@larry_n7luf What do you use and how do you use it?
I have been using “https://imgur.com/”
After you upload your picture to that sight, you need to go to your account, then go to images and click on your image and select Direct Link and past here in you message.
Larry – N7LUF
@Baron, I would leave the “Audio Amplifier Board” to one side for the time being and concentrate “purely” on the power supply. As a side note: an organised way of repairing anything electronic is to firstly deal with the power supply and if everything is “sound” then, and only then! move forward. (This is how I would tackle it). You need to do a thorough investigation and testing in regards with all the voltages that the power supply module ” Should” in theory deliver.
I’m thinking : if you really measured a “MINUS 48V on those wires the fault “MUST BE” on the power supply. Now….keep in mind that feeding the Audio module with voltages in reverse would “Very likely come with some “deep and nasty” re repercussions (IE: burned/shorted Power Transistors) and the red flag is simply the fact that you’ve had the dimm bulb circuit Lighting up “Brightly”. I would be extremely cautious around those (+) and (-) 48V voltage rails. That transformer is “A real Monster” and can put up a huge amount of current in the event of a “Short Circuit”. You don’t want to burn that transformer since it is almost impossible to find a replacement for it (unless you get it from a donner unit).
@ovi4 The power supply board 052 has close to proper voltage on pins 13 +42v and -42v pin 14. The wires are still connected to pins 14 and 29 on power amp board 030. I am getting -v on pins 14 and 29 on the power amp board without being connected to the power supply board. If I try and connect them to pin 13 on the power supply board 052 that is when I get the problem of the dim bulb tester getting bright.
All of the pins on the 052 power supply board have close to correct voltages. With the dim bulb tester on by-pass and running 115v from my power supply I am getting +42v on pin 13 and -42v on pin 14 of the 052 power supply board. This is why I suspect the problem is on the 030 power amp board but can’t figure out why, that is if I am correct in my thinking.
@larry_n7luf Can I upload a PDF file or does it have to be a pic file?
@john-barron I would say a PDF, you would have to post a link to the PDF file off site storage with permission to view it. “Like Google drive”
Pictures have to be from an off site storage like https://imgur.com/
Larry – N7LUF
@john-barron Well….The fact that you now saying that the (Minus 48V) comes from the Power Amp board and via the +48V wires there could be a number of reasons:
1. if you’ve fitted a new set of power transistors (since they are pairs of PNPs and NPNs) you’ve might have fitted them somehow wrongly : either you’ve fitted then in the right place but with the pins in reverse or you’ve fitted an NPN in the place of a PNP and the other way around way around.
2. if the transistors are are still originals They could be shorted. I would retest all 8 of them ! (The NPNs=Q1, Q2, Q7,Q8) and (the PNPs Q3,Q4,Q5,Q6)
I would also check (Q5,9,7,11), and (Q6,10,8,12)
3. a short-circuit on the PCB somewhere, perhaps a “blob of solder” somewhere etc.
Anyways, whatever the fault you have there, it surely “revolves” around the power transistors circuit somewhere and/or just before that.
I strongly suspect either shorted transistors or fitted wrongly.
Another thing: – if there are mica spacers/insulators needed when fitting the power transistors on sink? Make sure the insulators are fitted right verify the separation with an ohm-meter.
In the picture (below) the blue lines are the most possible current/voltage path from minus power rail to the plus power rail. The same path applies to the other channel since it has an identical topology and they are both fed with the same dual rail supply.
Keep in mind that the current/voltage always chooses the path with the least amount of resistance. And that could be as highlighted in blue if the power transistors are (some of them) shorted (E-to-C)
If after checking the above transistors and the integrity of the mica insulators (if there are any present) everything is sound (which I doubt by the way) you can try to tackle just 1 channel at the time and what I mean is that you need to identify the culprit area by only feeding one power amp at the time.
Now let me explain: you can disconnect the negative and the positive voltages from one channel (IE physically unsolder power rail wires from pins 15 and 30) and only leave connected the power on pins 14 and 29. (this way only 1 channel receives power) then try to power the unit slowly via the dimm bulb. If is sound then do the opposite and see how it goes. This way you can narrow down the faulty area.
@ovi4 Ok so I took all of the main power transistors Q1 through Q8 out and checked them. They are all good and are in the correct order. I did not put them back in and with the wire disconnected from pin 14 right where you have the red arrow I am still getting -42V coming out of pin 14 on the (030 board) with no transistors in place. And the dim bulb light is still bright. Looking at the schematic above and the power path I can only deduce that there is a short some where on the board that is allowing negative voltage to get from pin 15 to pin 14 (030 board) with no transistors in place.
Am I correct in this thinking or can negative voltage get to pin 14 on the 030 board from some other path without the main power transistors being ion place?
@larry_n7luf Yes this is the problem I can not put PDF files on IMGUR they want pic files. I just wish there way to add pics and pdf files here native instead of having to upload and link them. It takes time and causes problems with file conversion depending on what platform is being used.
@john-barron Yes it can. Via D11-Q11-Q9-D9 (if they are shorted). However, if you had current equivalents installed for (Q9, 11, 10, 12) make sure that they have the same pinout at the terminals otherwise you’ll need to bend the legs around to adapt it. !
Also, I know (I’m repeating myself but) check the integrity of the mica spacers and the other plastic insulators in relation to the power transistors on the sink.
Also check (visually) for any eventual “solder splatter” / “bridge” at the wires to the sink.
Remember that both channels are fed of of the same power rails so they are basically in parallel (from the DC rails point of view) So if you encounter (measure) a potential problem on the power rails of one channel it will be mirrored on the other channel as well So it would be impossible to distinguish if the fault is on one channel or the other therefore, a clear power rails (the wires) separation is required.
IMPORTANT: You need to leave the power rail wires on the power module “end” connected at all times and only ever disconnect power (when needed) from the power Amp end. very important to avoid confusion !.
Now regarding the output wires Pins (25,26) and (10,11) toward the speakers, make sure that you do not have any speakers, nor any headphones connected during the repair and is a good idea to check the output wires against Ground just in case there is a short to ground on them (you never know!) I would especially verify the integrity of the headphone jacks !
So the bottom line here is powerup only one channel at any one time. do some measurements than disconnect that channel and power up the other channel do the same measurements and see if it behaves the same. Having 2 identical power amp channels next to each other is a big advantage cos you can do comparisons between them.
@john-barron PS: here are some ” current day ” possible suitable transistor replacement equivalents. should you need to. Just make sure that the pinout is the same or you’ll need to bend their legs to adapt it.!
@john-barron The issue is John. When running a website (or Forum) you have a certain amount of file space allowed on the server that hosts your Forum. Pictures and PDF’s use up that space so quickly, that Mr.C’s allotted space will be used up in no time at all. This was the reason he requested people to host the artwork elsewhere and use links to it. I understand it’s a nuisance, but it does save someone having to go through the pages every month deleting peoples pictures/PDF’s.
Woodb180
@john-barron Some (kind of…) unlikely but possible accidental short-circuits on the Power Amp board via either soldering bridges or wiring posts touching each other to watch out for:
@ovi4 I had to go into the hospital for minor surgery on my right leg the other day and will be off my feet for a couple days. Nothing major so it will be a few days before I can get down stairs to my lab and let you know what I found. I’m going to have to check all of the transistors as I replaced them all. I don’t remember what the replacement part numbers were but I can look them up from the job order where I got the transistors from either Mouser or Digikey and let you know what I replaced them with. I will also reset all of the main power transistors with New Mica’s and heat sink compound checking for shorts between collector and heat sink. Then recheck the (030 board) for correct pinouts on the transistors and for solder bridges.
I am sure that one of these recommendations you have made must be the problem I just now have to figure out where I screwed up that part of the restoration.