trying to fix RANDALL RH-100 - need help

giokat · 23rd June 2011, 07:08 AM

Hi everybody,
I'm trying to fix a guitar amp from Randall, RH-100 G2.
Schematics is attached.
Some transtistors in the power amp were burned.
I replaced Q8, Q11, Q12, Q13, Q14, Q15 (!), D5, D7, R22.
I tested (with a simple tester...) the remaining semiconductors and they apparently are ok.
After the replacements the amp is in part restored. It 'almost' works in the sense that it sounds quite low in volume and always distorted.
I noticed that Q7 and Q9 are heating up a lot.
I measured 47V between Q9's emitter and ground and 0,2 V between Q8's emitter and collector. I think this is not normal.
Any help or suggestion? Thank you so much!
Regards!
Giorgio

sakis · 23rd June 2011, 09:54 AM

it could be that any of your balast resistors is open and you missed it check R14-15-16-17....check also R26-25

then check or remove temp. the vi limmiter section ( it will be enough to remove Q10-11 ) to make sure that the drive is free from the limiter in case you have any trouble there

giokat · 23rd June 2011, 10:26 AM

Thank you! I'm going to try.
What's the function of Q8 and Q6, in your opinion?
I figured out that Q8 sets the bias for the drivers, depending on the temperature (Q8 is mounted on the same heatsink as the power amps Q12.. Q15).
And what about Q6's function? I definetely miss some theory...
Thanks!
Giorgio

23rd June 2011, 09:54 AM	#2
sakis diyAudio Member Join Date: Jan 2006 Location: nea makri athens greece	it could be that any of your balast resistors is open and you missed it check R14-15-16-17....check also R26-25 then check or remove temp. the vi limmiter section ( it will be enough to remove Q10-11 ) to make sure that the drive is free from the limiter in case you have any trouble there __________________ SERVICE ΙΑΠΩΝΙΚΩΝ ΜΗΧΑΝΗΜΑΤΩΝ ΗΧΟΥ www.eastelectronics.gr

Thread Tools	Search this Thread
Show Printable Version Email this Page	Search this Thread: Advanced Search

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
RH ECL86 Amp: Dave?	pjanda1	Tubes / Valves	11	8th January 2012 08:44 AM
looking for Randall RH 100 G2 schematics	giokat	Solid State	2	24th May 2011 07:30 AM
Randall RGT 100 Amp Problem	GF33	Tubes / Valves	5	4th May 2010 02:47 AM
Counterpoint SA-100 Fix	genther	Solid State	2	11th April 2010 02:57 AM
RH-84 Hum	ThSpeakerDude88	Tubes / Valves	13	8th October 2009 04:48 PM

New To Site?	Need Help?
Register to Participate Search Privacy Statement Contact Us	Frequently Asked Questions Did you forget your password? Mark Forums Read


	Please consider donating to help us continue to serve you. Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving

23rd June 2011, 10:26 AM	#3
giokat diyAudio Member Join Date: Nov 2009	Thank you! I'm going to try. What's the function of Q8 and Q6, in your opinion? I figured out that Q8 sets the bias for the drivers, depending on the temperature (Q8 is mounted on the same heatsink as the power amps Q12.. Q15). And what about Q6's function? I definetely miss some theory... Thanks! Giorgio

Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)