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Post by mastertech on Mar 19, 2019 21:33:09 GMT -5
Well at this point, without the actual schematic for this unit I don't know. We have hunted around and I am sure we are missing something.
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nashou
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Post by nashou on Mar 19, 2019 21:39:11 GMT -5
Well at this point, without the actual schematic for this unit I don't know. We have hunted around and I am sure we are missing something. yeah, this is a tough one with out the schematic, is it safe to run the amp with out those driver boards? I could test with that. Now remember we have about 17 VDC with driver boards and output transistors out. for got what was said about that. No one on AK posted on a thread I started there , I liked them to this thread, Maybe some one there might have worked on one of these. There are a couple youtube videos of other Project/one amps but they are nothing like this. Nashou |
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Post by mastertech on Mar 19, 2019 21:49:31 GMT -5
I would be curious to see if that voltage was still there with those 2 boards removed. Was the relay latching with those boards removed?
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nashou
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Post by nashou on Mar 19, 2019 21:59:02 GMT -5
I would be curious to see if that voltage was still there with those 2 boards removed. Was the relay latching with those boards removed? yes it was, but remember the outputs were also removed. Are those safe with the driver boards removed? Also here are two pics of the boards, front and back. Maybe you can make something out of them. I am adding them because were kinda going off your schematic you first posted, those emitter resters are tied together in that amp, here they are not. I tested from end to end of each and if these are .5 ohm they should read 1 ohm or have at least continuity. these do not. measured out of unit and installed so they had the outputs connected.   |
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nashou
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Post by nashou on Mar 19, 2019 22:18:29 GMT -5
found this at a service manual seller. they have no info but this
Project/One was a house brand marketed by Playback Electronics (The Electronic Playground) in the 1970s in Chicago and possibly other places. We have heard various rumors of Project/One products being made by Pioneer, Hitachi, Matsushita (Panasonic /Technics), Micro Seki and others.
Not much help trying to go through all those schematics to find something similar.
THE Pioneer LX-880 USES FOUR OF THE SAME OUTPUT Hifiengine has the SM but the schematics are not the best.
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Post by stridsvognen on Mar 20, 2019 5:51:04 GMT -5
Sorry if i missed it, but is it possible to swap around the drive boards and see if the problem follows those, and then swap the output transistors, to clear or locate the error to that part of the amp.?
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nashou
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Post by nashou on Mar 20, 2019 7:03:04 GMT -5
Sorry if i missed it, but is it possible to swap around the drive boards and see if the problem follows those, and then swap the output transistors, to clear or locate the error to that part of the amp.? Hi Kurt, Well both amps show DC on the speaker outs. just one is a 1.5 volt higher i would say. I could swap the driver boards between output transistors easily. I can do that later today when I get home. On the 2SD188's do you mean swap them on the heat sinks they are on already? Or to different heat sinks? But what we saw was with boards and output transistors out of the chassis was still a 17 vdc on the left output only. The right had none at all. So we think there is some getting to the out put somewhere else. So we are missing something. Also the schematic we are looking at is one we think is similar, but now I have my doubts as on that schematic the two 5 watt emitter resistors are tied together. and on this unit they are not. So I looked for possible amps that had all 4 outputs of the same transistors on the rumors that Project amps were clones or designed after either Pioneer and those other companies. The Pioneer LX 880 looks closer to what we have here. So we might be looking for the wrong issue. BUt I still wonder if I can try the receiver with the amp boards out but the SD188's still installed? We'll get this sorted !!! |
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Post by stridsvognen on Mar 20, 2019 7:25:34 GMT -5
If you can swap drive boards, and if the issue dont follow those, then swap heatsinks or the tranistors, just to rule that out, if the problem dont go with any of those they are cleared and its easier to focus elswhere, or if the problem goes with the drive board it would be asy to swap around some of the small drive transistors one at a time. And as i understand it the trimmers had a effect on heat, so i would turn them all down, and with everything in place measure the mVdc over the emitters, and im sure you will see that there it relates to the heat.
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nashou
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Post by nashou on Mar 20, 2019 7:33:31 GMT -5
If you can swap drive boards, and if the issue dont follow those, then swap heatsinks or the tranistors, just to rule that out, if the problem dont go with any of those they are cleared and its easier to focus elswhere, or if the problem goes with the drive board it would be asy to swap around some of the small drive transistors one at a time. And as i understand it the trimmers had a effect on heat, so i would turn them all down, and with everything in place measure the mVdc over the emitters, and im sure you will see that there it relates to the heat. Yeah I meant to try to swap driver boards but never did. The heat sinks have the connector block attached so I cant swap them with out major desoldering of wires . One thing I did notice is a cap ( Green) from the collector to Emitter on the one output transistor that is the actual output transistor. Here I marked up the picture ( couldn't figure out how to make text larger) maybe those are bad or shorted?  |
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nashou
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Post by nashou on Mar 20, 2019 7:41:51 GMT -5
Kurt, adjusting the trimmer to 5mv both heat sinks stay very cool. 79F° to 83F° on both heat sinks. However at that setting DC on speaker outs are 3vdc and 5 vdc.
If I adjust trimmer to lower DC at speakers then heat goes way up to 230-250 F°
At work till 4 today will swap out boards later.
Nashou
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Post by stridsvognen on Mar 20, 2019 7:48:10 GMT -5
My experience is that its normaly a transistor that trows off DC, even you test them and they measure ok on your tester, so i would definatly make sure that all your small and output tranistors are cleared/ swapped around.
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nashou
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Post by nashou on Mar 20, 2019 8:20:48 GMT -5
My experience is that its normaly a transistor that trows off DC, even you test them and they measure ok on your tester, so i would definatly make sure that all your small and output tranistors are cleared/ swapped around. Yeah I guess I'll move from the amp I did not recap to the one I did. there are 4 transistors on those boards, three heat sinked and one not. But here is the pioneer LX 880 amp, it looks more like mine than the one posted earlier in the thread. What do you think Mac?   Even the power supply is similar 2200uf 63 volt filter cap  |
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Post by mastertech on Mar 20, 2019 14:28:43 GMT -5
That amp has 2 pots per channel. But you can see the filtering going on on the output lines.
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nashou
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Post by nashou on Mar 20, 2019 14:57:22 GMT -5
That amp has 2 pots per channel. But you can see the filtering going on on the output lines. yes I see that but couldn't my amp be using differential pairs to set the DC offset? If you look at the schematic the two emitter resistors are not tied together like in the amp schematic you posted. So this seems to be closer to the amp i have. Also the way the one emitter goes through the .5 ohm resistor is the same as it is on my amp I believe . Another difference is mine has 4 transistors before the output transistors where two are the same, this has me thinking they might be a differential pair. But not 100% certain. School me on this  |
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Post by mastertech on Mar 20, 2019 15:42:21 GMT -5
Don't get me wrong, it may be closer. But how does it help us at all if there are still uncertainties. Plus I looked through this manual and it does not have a description on adjusting those pots. Also does not have any voltage listings. So I don't know if it helps or not.
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