Randall RG100 Classic info?

[TolerBear]

Dang you said the voltage on the zener. I forgot to measure that. I'll do that tomorrow too.

[Roly]

Dang you said the voltage on the zener. I forgot to measure that. I'll do that tomorrow too.

{#$%& man, the suspense is killing me}


I predict...

...that both the 33V and 24V lines will be low.

[TolerBear]

Lol. I'm sorry!    :-D

[TolerBear]

So I measured it today and I found that the voltage on the zener is 1.6 volts dc. The other way it shows 0 volts. I got busy and I wasn't able to do any other measurements. I'm hoping tomorrow to do more measurements. I don't understand this thing. I'll talk to y'all tomorrow. I'm soooo grateful for y'all's help. I haven't said that yet but I am.

[g1]

  Measure the resistance across D4 (regulator input) and C18 (regulator output).

[Roly]

So I measured it today and I found that the voltage on the zener is 1.6 volts dc.

Powered up we mean; if it's +1.6V one way it should measure -1.6V with the probes reversed.  Measurements on an unpowered zener are almost meaningless (unless it's shorted).

This should be 33V.

Pull connection P2 between Power Amp PCB and Front Panel PCB, and see if 33V input and 24V output supplies are restored.
Post results.

Personally my money is still on a shorting op-amp on the board, and these can be tricky to locate.

On the circuit <RG80-Schematic-1.jpg> (upthread) the 24V goes to the bit in the middle where it becomes VC1 and VC2.

If you had a short on VC2 then R26 would be letting you know, so it has to be on VC1 rail.  A few things run off this, FET preamps mainly that are incapable of drawing significant current even if they wanted to.

So, the reverb driver and recovery is U1, a 4558, which is right on the VC1 rail.

There are a couple of caps, but that's my hit pick of the week.


I can bearly tolerate this drip feed... 

[TolerBear]

Lol. I'll check it asap. I have a dentist appointment this evening so it may not be until tomorrow when I get to it. Drip.....Drip.....Drip :duh

[TolerBear]

And I powered it up when I measured it.

[g1]

attached is the elusive schematic for this version, full page view on page 5 of pdf

[J M Fahey]

Thanks  :dbtu:

[Roly]

Me too.   :dbtu:

I do hope TolerBear hasn't gone and done something rash.   

[TolerBear]

Sorry y'all.  My phone died and I had to get another one.  This is awesome!  I'll check it ASAP.  I had a 300 ohm resistor and it looks like it calls for a 330 ohm.  Is that enough to make it act like it is or should I be looking elsewhere still?  Btw it sucked being away that long.  Lol.  May God bless each one of you.

[Roly]

330 ohm is the common value, close enough, anyway can tweek later if needed.

[TolerBear]

Hey. I gave up on the Randall for a while. I replaced the regulators and output transistors and it  kinda worked for a bit in that it had a hum going through it for a bit but it never passed a signal. I'm gonna start working on it again soon I just got aggravated with it. Also I had a couple circuit tracks that lifted and I think some of the through the board hole taps came out. Ugh! xP