K200 Repair PC203 Board Issue [message #28138] |
Wed, 24 March 2021 23:39 ![Go to next message Go to next message](/FUDforum/theme/vk30/images/down.png) |
g2s
Messages: 4 Registered: March 2021
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Junior Member |
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Hey all,
I have a K200-B1 that I'm on the home stretch of repairing.
It has low output when plugged into the 'Boost' channel that runs through the PC203 board.
Everything is working up until Q203. I have replaced Q203 with a 2N4401.
Plenty of signal at the base, low signal at collector. Voltages are B: 2.4VDC C: -0.55VDC E:GND.
The schematic shows the Base voltage should be +6V. Is that right? Possible mis-print? I can only see how it is connected indirectly to the negative rail, so how can it have a positive voltage?
Not sure what else to check here. Here is the schematic: shorturl.at/xLUV8
Any suggestions are appreciated! A lot of great info on this forum I am continuing to read through it now.
Thanks in advance.
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Re: K200 Repair PC203 Board Issue [message #28139 is a reply to message #28138] |
Thu, 25 March 2021 05:54 ![Go to previous message Go to previous message](/FUDforum/theme/vk30/images/up.png) ![Go to next message Go to next message](/FUDforum/theme/vk30/images/down.png) |
stevem
Messages: 4763 Registered: June 2004 Location: NY
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Senior Member |
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Hi to ya!
Don't use the pc203 schematic on our site , use pc303 and look at Q303.
That base voltage should be + .6 , not plus 6 volts, that 203 schematic lost its dot in the copy process somehow!
If you have no proper way to test out C222 for leakage and ESR then I would for atleast replace it with something close, like even a 5 uf filter at the needed voltage or better, or even a 50 uf of the same voltage detail.
PS, 203 is not connected to the -8 volt rail .
I would also confirm that c212 is not leaky just to cover all the bases!
I would also test or replace c213 and check if r219 is within its tolerance range .
Let us know how it goes!
[Updated on: Thu, 25 March 2021 07:24] Report message to a moderator
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Re: K200 Repair PC203 Board Issue [message #28140 is a reply to message #28139] |
Thu, 25 March 2021 10:12 ![Go to previous message Go to previous message](/FUDforum/theme/vk30/images/up.png) ![Go to next message Go to next message](/FUDforum/theme/vk30/images/down.png) |
g2s
Messages: 4 Registered: March 2021
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Junior Member |
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Thnaks for reply Steve.
Quote:Don't use the pc203 schematic on our site , use pc303 and look at Q303.
If someone wants to send me the pc203 schematic I can add a dot that looks original. Just let me know and I'll PM an email address.
Quote:If you have no proper way to test out C222 for leakage and ESR then I would for atleast replace it with something close, like even a 5 uf filter at the needed voltage or better, or even a 50 uf of the same voltage detail.
I do have means to test for ESR and Leakage but if I'm going to pull the cap I'll just replace it. I suspect shotgunning all those 50 year old tantalums would not be a bad idea, but I prefer to only change things I suspect and I wasn't sure what to suspect here.
I pulled C222 and replaced with a 33uf electrolytic. The old tantalum reads 30uf ESR 1.4ohms, not bad.
No change to base voltage of Q203 -0.56V.
Quote:I would also confirm that c212 is not leaky just to cover all the bases!
I would also test or replace c213 and check if r219 is within its tolerance range .
R219 seems fine, 11K.
Replaced C212, no change.
Replaced C213, no change.
Quote:PS, 203 is not connected to the -8 volt rail .
I see bottom line of the schematic Green Wire -8V, no? My board definitely has the green wire with -8V. Not sure what I'm missing.
Thanks again!
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