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Topics - Jude

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The Newcomer's Forum / Fender Frontman 212R hum and volume 80% down
« on: February 05, 2021, 05:26:36 PM »
Hi folks,

I am trying to repair a Fender Frontman 212R, that powers on ok but has hum and low output volume (around 20% of what it should be at full volume). I am new to electronics theory and amp repair but I can competently use a multimeter and soldering iron!

I followed the steps in an earlier  post (https://www.ssguitar.com/index.php?topic=3741.0) to try and isolate where the defective component is and measured the following voltages with the amp powered on (some values do fluctuate):

1. has 44 VDC at the main power caps at C71 and C72 ( I have linked the schematic below)
2. 16.5V VDC at C75 and C76
3. R87 and R88 44V, R89 and R90 -44 VDC, R102, R104 and R106 -0.5 to 1 VDC
4. PNP transistors at Q9, Q10 and Q11

Q9 E: 0.55 VDC, C: 43 VDC B: -0.45 VDC
Q10 E: 0.56 VDC, C: 43 VDC B: 0.05 VDC
Q11 E: 44 VDC, C: -26 VDC B: 43.7 VDC. from what I read in the earlier post Q11 should read 42V at C, I did repeat readings and measured either 41V or -26V at Q11 C.

So Q11 seems suspect and with the amp powered off I checked the readings at Q11 E-C, C-B and E-B. Everything read OK apart from C to E which read 1.6V and not OL suggesting a short.

After all this poking around the amp now has now sound at all!

Would an pro members like to give me some quick guidance on this? I was planing to order a replacement for Q11 unless my conclusion is wrong.

cheers from down under

Jude

Schematic:

https://elektrotanya.com/fender_frontman_212r_sch.pdf/download.html

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