Penta I amps, two different problems, orange lights of doom

6 replies
C(
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cordobaman (archived2)
Bronze
Posted May 11, 2014 at 04:13 GMT
#2200023

Problem #1: One of my Penta amps is not doing well. As it warms up, a crackle/static develops, grows louder, them "pops". The static will stop, then gradually start up again. If I continue to play the amp for a while it will go into orange mode.  What should I look for to repair?

Problem #2: I really feel stupid for this one. I was upgrading a spare Penta 1 amp, new opamp, re-capping.  As I was testing my completed project, the input bracket shorted against the bottom of the circuit board, small sparks, and sniff of smoke. I think I'm going to be sick.  Now the amp goes orange when I try to turn it on.  What might have I damaged?

Thanks in advance for a reply to either of my woes...

BO
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bos00
Bronze
Posted May 11, 2014 at 09:16 GMT
#2200024
#1 trimmers & caps.

#2 any semiconductor(s).
C(
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cordobaman (archived2)
Bronze
Posted May 11, 2014 at 13:37 GMT
#2200025

Thank you very much BO for your reply!

1. I suspected as much...that one is easy.

2. This could be a challenge. Being that the amp starts red, then goes orange upon an input signal, any hints as to which semiconductors I should replace first?  Are you including the output transistors in your statement?

JÖ
Offline
Johan Östlund
Bronze
Posted May 11, 2014 at 16:37 GMT
#2200026

cordobaman wrote:

Are you including the output transistors in your statement?

Yes, that's likely.

/  Johan

BO
Offline
bos00
Bronze
Posted May 11, 2014 at 19:01 GMT
#2200027

Orange light may indicate shorted/broken output transistors. Measure them and replace if found faulty. Measure all semis in the areas where you had the short. When powering up use a light-bulb dimmer with, and slowly increase voltage. Monitor zero-voltage current.

 

Beobuddy
Offline
Beobuddy
BronzeFounder
Posted May 26, 2014 at 13:18 GMT
#2200028

A broken/burned ground trace on the circuitboard could also be the cullprit.

BTW, small detail, it's Monitoring the output zero-voltage and idle current.(30mA/30MV accros R103/104 or a bit less).

Location: Utrecht

Quite a challenge to achieve "Less is More" while having the Beovirus.
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