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Winston Winston is offline
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Default Grundig AM/FM portable "Transistor 305" troubleshooting

Sylvia Else wrote:
On 7/03/2012 11:41 AM, Winston wrote:
Sylvia Else wrote:
On 7/03/2012 1:46 AM, Winston wrote:
Sylvia Else wrote:
On 5/03/2012 2:47 PM, klem kedidelhopper wrote:


(...)

http://dl.dropbox.com/u/65394789/Gru...0schematic.pdf

Voltage readingso
Test point Radio working: Radio not working
------------------- --------------------
-------------------------
E. AF178 -1.10V -1.20V
B. AF178 -1.50V -1.50V
E. AF124 -1.10V -1.20V
B. AF124 -1.32V -1.44V
E. AF121 -0.85V -0.90V
B. AF121 -1.20V -1.30V
E. AF126 (1) -1.00V -3.70V *
B. AF126 (1) -1.20V -4.00V *
E. AF126 (II) -0.80V -3.70V *
B. AF126 (II) -1.10V -3.60V *
E. AC151 (I) - 0.90V -0.80V
C. AC151 (I) --3.05V -2.95V
E. AC151 (II) --0.66V -0.62V
C. AC151 (II) --3.20V -3.10V

Thanks once again for looking. Lenny


(...)

As Frank observes, if the 1.4 St1 connections are compromised, then
the bias for the AF124 would be affected, and on the
OP's readings, it is not.

Now, we don't know the nature of the link between that diode and pin
ten of F IV, and I've seen Grundig do some rather
questionable things, but if it's just a circuit board track, the fault
pretty much has to lie either in the pin 10
soldering, or in the track itself.


Good point.

I look forward to what Lenny eventually discovers.

Given the history of the radio, a cracked trace
would not be out of the question.

It'll be amusing if it was C4 or C38 or R22 that was
intermittently shorting, instead.


I don't think those could cause the observed effects - they'd all pull the transistor base down to -9V, near enough.


I hope Lenny will get back to us with his findings.



--Winston