Hacker Grenadier GP45

[recordplayer]

Hi , I am working on this player after a botch job by someone else - the 4000uf smoothing cap had failed so replaced that and given the deck a service . The problem now is low sound - the h.t. is correct and I have replaced the Acos GP104 cartridge with a good working GP104 . If I feed a radio into the sockets on the right and adjust the volume on the radio the sound is as it should be - loud and plenty bass and treble . If I feed the radio straight onto the pick-up tags on underneath the deck it's the same - it's not the cartridge or the pick-up arm wiring that's faulty - this leads me to think it's a fault on the pre-amp panel - any ideas ?

[Edward Huggins]

If you do not have the Service Sheet for this it can be downloaded from this site, see top RHS of this screen. From memory this unit uses 5 transisitors and I do not think there is a discrete pre-amp stage for the Acos ceramic cartridge. This cartridge would not normally need one. It still sounds like a wiring problem or oxidised connectors.

[Audio1950]

Surely if you're connecting the radio onto the tag strip under the deck, and that works ok, then the fault MUST be before there, i.e the cartridge? The pre-amp panel must come between the tag strip and the main amp. Are you sure you've connected the wires to the cartridge in the right positions?

[Station X]

Won't a radio be giving far more output than a cartridge? The OP refers, I think, to adjusting the radio's volume control.

I'd have thought checking voltages in the preamp was the next logical step.

[recordplayer]

Yes I use a radio to feed a sound source into the pre-amp, because an MP3 player is a very low output and the radio is adjustable output wise by the volume control for testing. As I said I have fitted a known good GP104 with no tarnished connectors, and correctly and checked the pick-up arm wiring for shorts. Will check it again to be sure, but I think this is going to be a fault on the pre-amp board which unfortunately has been botched previously with poor soldering. Ideally I would like to swap the panel with another just to be certain the fault is on there as the customer doesn't want to spend a fortune on the repair !! If anyone has a good spare panel to lend that would be great - suppose it's worth a try asking !

[Edward Huggins]

By "Pre-Amp Board", do you must mean the transistor stage that preceeds the AF and Driver transistors. Surely this will serve all signal sources.

[recordplayer]

The pre-amp board is the board with the volume , bass and treble controls - this then feeds the main amp module , I have the service info so I may have missed something - suppose its back to the workshop with a fresh mind !

[recordplayer]

Hi Edward , this is the pre-amp board - ideally I would like to change this to be sure the fault is on this loaded if anyone has a good working board I can borrow - then proceed from there , Tony .

[Herald1360]

Just for clarity, the GP 45 does have a separate tone control/preamplifier module. The extra gain provided is used to overcome the losses in a passive Baxandall tone control stack.

Whilst the main amp may well have enough gain for a ceramic cartridge direct, it's not done that way- the player is further upmarket than that!

[mhennessy]

The way to check the overall gain of the system is given in the manual - why not just do that rather than speculate?

You feed in 10mV at 1kHz to the RH Radio socket. With the volume control at max, bass and treble at their mid positions, you should have 10.2 volts at the output of the power amp. You'll want to replace the loudspeaker with a 15 ohm dummy load (or wear ear plugs!) while doing that.

As the sensitivity is so high, an MP3 player should have no problem developing enough voltage to drive it. Why don't you measure the voltage output of the MP3 player to establish this is the case?

If the overall gain is low, then is it the preamp or power amp? Hacker don't give a spec for the sensitivity of the power amp, but you can work out what it should be from the component values, and then measure it accordingly.

Finally, if the overall gain - via the radio input socket - does appear to be OK, then bear in mind that the radio input socket has contacts which allow the signal from the pickup to be interrupted by the incoming radio signal when the plug is inserted. These have to make good contact when there is no plug in the socket. Could these have tarnished? Based on the original post - where you say the radio is OK via the socket but quiet via the pick-up tags - this seems to be a strong possibility... Either that, or a short-circuit on the pre-radio socket wiring.

[recordplayer]

Hi , I have already cleaned the radio / tape input sockets and no short there or open circuit circuit - will carry on fault finding and post outcome as I proceed

[recordplayer]

Think this is going to be a no-go - the customer took it to an engineer whose charged him £87.50 and didn't cure the fault - I have advised him to ask him for his money back or tell him to repair it . As I give free estimates I can't spend any longer on this because basically I am trying to rectify someone else's botch job - the soldering work is appalling and he had already missed seeing the smoothing cap that was faulty !

[AC/HL]

I remember from my stint on the production line, wiring issues can produce completely illogical fault symptoms that just couldn't happen normally. Unravelling the "botch" could prove time consuming. You're probably right to disassociate yourself with it.

[mhennessy]

It still could be something as simple as the Radio input socket. In case I wasn't clear enough, I'm referring to the contacts inside the socket that carry the signal through when there is no plug in the socket. This is the classic problem that affects the 3.5mm headphone sockets on Roberts/Hacker/others radios - though it can happen to any socket that contains switching contacts. It's the only logical explanation for the fault as described so far.

Cleaning the socket - to ensure a good connection between the socket and an inserted plug - might not be enough to cure a problem with the "normalling" contacts. Of course, a simple check with a multimeter is all it takes to check the contacts.

[Edward Huggins]

This "botch job" situation really distresses me for a mix of reasons. The few side-street repair shops that are now left, are mainly run by general purpose, ex. TV engineers, struggling to make some kind of a living. "New-to-vinyl" customers are often being charged typically around £100 for very basic check overs. BTW, this is not a criticism of TV Engineers, but think about it, just who does a youngster with a faulty player take it to these days?

[recordplayer]

I have already cleaned and metered the radio contacts as I said in my earlier post and I am aware that they give trouble as in the Hacker Cavaliers and Gondoliers - so those HAVE been eliminated - in fact I even shorted the switch out and got right into the contacts to clean them properly not just with switch cleaner - anyway thanks everyone for the input but this one will have to wait for a good preamp panel to swop over or its going back to the customer - time is money !

[mhennessy]

OK; I apologise if you feel I was stating the obvious, but I can only go on what you've written, and from that, it wasn't clear if you'd a) understood what I meant by the "normalling" contacts in the switch, and b) you'd specifically cleaned those in addition to a general clean.

It's a shame you're giving up, given that you've already changed that cap and serviced the deck. I'm sure it'll be easy to fix, and I for one would love to know what the fault is. Were you able to perform any of the measurements that I suggested in post #10?

[Edward Huggins]

I would not like to be beaten by this either, especially as the chance of sourcing a spare pre-amp board is highly unlikely, unless another player is (pointlessly) cannibalised.

I would want to go over every connection with a signal injector.

[recordplayer]

Unfortunately there is only so much time I can spend on this due to hospital trips and family commitments and the amount the customer wants to spend on his limited budget so will hang on to it for a while - maybe a panel may turn up - who knows !

[Michael Maurice]

I think to be fair to both yourself and the customer, tell him you've gone as far as you can and that if he wants more diagnostic work carried out it will not be free of charge.

Looking quickly at the diagram, all sources go into the preamplifier at the same point save for the switching. ie there's no extra amplification for the pick up. Which leaves the sockets themselves, the pick up or the wiring. If the sockets are faulty then its unlikely to affect both channels in the same way