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Fisher rs-2010 goes into protect mode instantly

S

suzook

Active Member
Just picked up a rs-2010 for a parts unit, but it's a beauty, so I'm thinking I should try and fix it. Unit powers on, then relay clicks, and then clicks off. Wondering where I should begin??? Strange thing is after the relay clicks into protection, I shut it off, and the protection mode stays on. That doesn't make sense to me. Thinking I should 1st discon the stk power packs. Thoughts?
 
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Ok, pulled the offending stk pack, popped a old spare in, the other channel produces sound, the bad one no output. So obviously something in the chain is bad. Gonna test good side, against bad side on amp board. Anyone have any ideas?
 
Welp, q 17, and q 19 i think are toast, they have a short across the 3 legs. Also, I found r59 toasted. I temporarily put a new resistor in r59, and it gets hot quick, thinking because q17, and q19 are bad??? Looking for advice. What is a good sub for a 2sa1016k??? I have some ksc992's laying around, I think they are compatible?
 
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ecluser said:
You mean KSA992? OK for the 2SA1016k but Q17 and Q19 are NPNs, not PNPs.
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UM, I'm a dummy. LOL. Definitely Q17, Q19, they read short, So i need 2 2sc2362. Need to find their alternate. Looks like ksc1845 should be replacements, and I happen to have some! Any other components I should check? So 2 transistors, 2 resistors bad, assuming from the shorted/blown STK.
 
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Surprising that Q17, Q19 are shorted. There is so little current in these transistors. I would suspect more Q11, and to a lesser degree Q09.
 
ecluser said:
Surprising that Q17, Q19 are shorted. There is so little current in these transistors. I would suspect more Q11, and to a lesser degree Q09.
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I'll double check again, but it's not a solid short, but meter on capacitor mode, I get continuity across the legs, that doesn't happen on the working side. Reading the service manual, looks like one leg should be 56v, no? Sorry,I'm a bit of a new, so bare with me. Please. Appreciate the advice.
 
Meter on capacitor mode??? There is an error on the schematic. The voltage on the collector of Q17 is -55V, not -44.3V as shown on the schematic. In fact, the voltages on base, collector and emitter of Q17, Q19 are all within 1V around -55V.
 
I'm going to take the r59 out, take some voltages again. I know for a fact I was getting -55v on one side of most resistors, and only 1v on the other if that makes sense? My issue is where to start? again, I am a newb. I'm wondering why I am getting so involved, this was supposed to a parts unit, but I am determined to fix it.
 
I wouldn't put a new STK, not even a good used one, before checking the rest of the circuit. Pull out Q11 and check it on a transistor tester. Check R31 and replace R59. If you want to play safe for your replacement STK, remove the STK and install two resistors of the order of 240 to 300 Ohms, one between the pins 1-3 and the second between pins 8-10. The purpose of these resistors is to close the signal path. If all is good, you should have 0 offset and be able to listen with a pair of headphones.
 
I'm thinking this guy is just gonna sit on a shelf for now. I did buy it as a parts unit. Would be nice though if I can figure out what needs to be fixed. Inside is spotless, along with the case and front.
 
A little more testing, pulled r 59, as that burns up if left in...So I am getting 55v on one side of most other resistors in the circuit, but only 1v on other side of the resistors. I get 55v on both sides od resistors on good channel. Not sure where to begin

Edit, so Q11, in circuit reading 9.9kohms across leg, while q12 on other side measures, .9kohm. I will pull q11, and test further...also Q7 measures weird in circuit.
 
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You must know one important thing about this circuit. There is very little current in Q05, Q07, Q17 and Q19, less than 1mA in each one. So, the chance they go bad is very small. In Q09 there is 5mA but the mean voltage across Q09, from emitter to collector, is of the order of 55V so it dissipates about 300mW. Enough to be hot if there is no heat sink to Q09. For Q11 the situation is more complex. The collector current in Q11 can be much higher than his counterpart (Q09) and it is why this transistor is the most likely to fail. The collector current of Q11 is limited by R31, R59 and the base resistor of the PNP driver transistor inside the STK0105. That base resistor is of the order of 350 Ohms. If you can't test Q11, replace it. KSC3503, TTC004B, KSC2690, TTC011B are good substitutes.
 
ecluser said:
You must know one important thing about this circuit. There is very little current in Q05, Q07, Q17 and Q19, less than 1mA in each one. So, the chance they go bad is very small. In Q09 there is 5mA but the mean voltage across Q09, from emitter to collector, is of the order of 55V so it dissipates about 300mW. Enough to be hot if there is no heat sink to Q09. For Q11 the situation is more complex. The collector current in Q11 can be much higher than his counterpart (Q09) and it is why this transistor is the most likely to fail. The collector current of Q11 is limited by R31, R59 and the base resistor of the PNP driver transistor inside the STK0105. That base resistor is of the order of 350 Ohms. If you can't test Q11, replace it. KSC3503, TTC004B, KSC2690, TTC011B are good substitutes.
Click to expand...
Ok, that makes sense, as r59 was toast. I think I will just replace Q11 for now. Thanks
 
I just happen to have a ksc3503 from a kit for my sx-800, that I never got around to. Will pull Q11, and put this in. I am worried about something else frying it though.
SO q11 is out, it measures open across all legs. Theres a resistor from one leg to the other, should i put that back?? Doesn't show in sm
 
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I replaced Q11, r 59 still getting hot!!!!, R 31 tests good, and doesn't get hot. Unit doesn't come out of protection.

OK, found R35 open, replaced, plug in, both R35, and R59 smoke. Still something wrong. ANy ideas?? Thanks
 
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