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Model 32 not starting up

M

MrJackson

Member
So... I was just preparing to start my Model 33 restore when suddenly, one morning, my Model 32 refused to start up - the relay isn't kicking in. Professionally serviced my a**.

Usually, the transformer starts buzzing louder and louder until the relay kicks in and then it's quiet. Now, it just emits a faint buzz and that's that. Pilot lights are fine.

I've connected it through a DBT, but there doesn't seem to be any short. I've then proceeded to do some measurements to see what going on. I started with Vac across CR302 and CR303, which is at around 28.2V (still on the DBT). That seems fair, I think (half wave of 60Vac). The voltage across the reservoir caps and R307/307 is equal at around 33V.

There's some 7Vac across R309 and about 6V across R306. There's 0.25Vdc across R310. Lastly, I measured 22Vdc at Q302's can (which I assume is the collector).

Last but not least, I've measured 1Vdc across C302 (which seems to have been replaced with a smaller 100uF / 10V cap).

I'm still trying to figure out how the whole thing works and which voltages are out of spec. Any suggestions are more than welcome
 
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Ok, so I left out the DBT since there's no apparent short.

I think I'm starting to understand how this works, bit by bit. Without removing the relay board, I've measured the input of the relay and it's at 26.7V. The output of the relay measures ~21V (it seems to slowly drop over time) and R310 drops about 2.3V. The emitter of Q303 seems to be at 0.5V - shouldn't this be higher? Its gate is at 1V.
 
^^^ Indeed. Could be that there's limited experience out there on this very early solid state model. I'll take a crack at it.

It sounds like it was not working right before with the slow build up of buzzing of the relay and it's just gotten to bad to now operate. It could be that 1.0 volts at the base of Q303 is not enough to fully turn on both it and Q302. For sure Q302 is not saturating as the collector would be a lot lower in voltage. It could be that Q302 or Q303 have gotten very low in gain but the greater possibility is that C302 has gone leaky or if replaced is in backwards even. It is the "timing" cap that causes the delayed turn on time. It is charged through resistor R309 a 510K. Check that R309 is still near it's value of 510K or whatever it's marked too. A dim possibility but worth checking is if R306's value has gone down from 39K but VERY doubtful.

All of this assumes that the amps have a dc voltage offset of near zero volts DC. That can be measured at the relay board pins 1 and 16 or at the summing point at the junction of resistors R302 and R305.

Good luck and let us know!
 
rBuckner said:
^^^ Indeed. Could be that there's limited experience out there on this very early solid state model. I'll take a crack at it.

It sounds like it was not working right before with the slow build up of buzzing of the relay and it's just gotten to bad to now operate. It could be that 1.0 volts at the base of Q303 is not enough to fully turn on both it and Q302. For sure Q302 is not saturating as the collector would be a lot lower in voltage. It could be that Q302 or Q303 have gotten very low in gain but the greater possibility is that C302 has gone leaky or if replaced is in backwards even. It is the "timing" cap that causes the delayed turn on time. It is charged through resistor R309 a 510K. Check that R309 is still near it's value of 510K or whatever it's marked too. A dim possibility but worth checking is if R306's value has gone down from 39K but VERY doubtful.

All of this assumes that the amps have a dc voltage offset of near zero volts DC. That can be measured at the relay board pins 1 and 16 or at the summing point at the junction of resistors R302 and R305.

Good luck and let us know!
Click to expand...

Mine is on its deathbed as well..
No issues with the relay buzzing or failing to click over. There was only one time that buzzing could be heard coming from the transformer but had not returned so far. DC offset on the right channel started at 80mv and steadily climbed to over 100mv while left channel was around 35mv. Very noticeable humming comes through the right speaker that is constant and does not change with volume attenuation. Right heat sink gets hot enough to cause discomfort to the touch.
 
Does the 32 use the large bias pot like the 16's? Maybe they have carbon build up, or a wiper is getting flakey? It's easy enough to check with a DMM to see if they are tracking properly.
 
Original problem 27 volts going to relay is too low. Voltage and symptoms suggest C303 is open. Try changing C303 10uF cap. Don't increase cap value, but increasing cap voltage is not a problem. Cap going bad will buzz on turn on, or intermittent relay.
DC offset issues are nearly always differential pair (Q201 and Q202)
 
sregor said:
Original problem 27 volts going to relay is too low. Voltage and symptoms suggest C303 is open. Try changing C303 10uF cap. Don't increase cap value, but increasing cap voltage is not a problem. Cap going bad will buzz on turn on, or intermittent relay.
DC offset issues are nearly always differential pair (Q201 and Q202)
Click to expand...
I haven't downloaded loaded the schematic, but is that 10uf cap one of the Axials on the relay board? When I restored a model 16 and model 33 preamp, all the axial caps had dried out crumbling seals. A few were pretty dried out.
 
Lavane said:
I haven't downloaded loaded the schematic, but is that 10uf cap one of the Axials on the relay board? When I restored a model 16 and model 33 preamp, all the axial caps had dried out crumbling seals. A few were pretty dried out.
Click to expand...
Shown as axial in the manual/
 
The Axial's I found in those two pieces of Maranz equipment, along with a few others, were sketchy 10 Years ago when I replaced them. By now using this early Marantz SS gear unrestored is risky.
 
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