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July 02, 2020, 02:36:58 AM

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Author Topic: 1988 Randall RG100ES  (Read 2034 times)

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Re: 1988 Randall RG100ES
« Reply #30 on: January 01, 2020, 10:17:53 PM »
when checking them against the schematic they are all close. So if there is 42v at the base of say Q11 where the schematic says 38v is that enough to cause issues ?

Loudthud

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Re: 1988 Randall RG100ES
« Reply #31 on: January 02, 2020, 06:10:10 AM »
Have you checked the low value resistors R55, R56, R57 and R58 ?

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Re: 1988 Randall RG100ES
« Reply #32 on: January 02, 2020, 09:53:20 AM »
Yes they all test good

g1

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Re: 1988 Randall RG100ES
« Reply #33 on: January 02, 2020, 01:38:29 PM »
when checking them against the schematic they are all close. So if there is 42v at the base of say Q11 where the schematic says 38v is that enough to cause issues ?
Maybe. (and I think you meant Q10; too many errors in your posts, please try to be more accurate)
Each transistor needs a difference in the range of approx. 0.5 to 0.7VDC between the base and emitter.
That difference is what tells you whether the transistor is running or not.
So Q10 (PNP) with 42V at the base is only ok if it is roughly .5V less than the voltage at the emitter.
For NPN types, the base needs to be approx. .5V more than the emitter voltage.

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Re: 1988 Randall RG100ES
« Reply #34 on: January 02, 2020, 02:04:18 PM »
The base of Q10 is 43.5 v the emitter is 44.0v

Jazz P Bass

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Re: 1988 Randall RG100ES
« Reply #35 on: January 03, 2020, 01:30:01 AM »
I am stuck on the squirrely voltages on Q8.

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Re: 1988 Randall RG100ES
« Reply #36 on: January 04, 2020, 01:29:58 PM »
I have found a couple 2n5484 transistors bad TR1 and TR5 so far. Not sure what effect that would be having on the power section but need replaced